1 /* 2 * Copyright (c) 1998, 2020, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "classfile/vmSymbols.hpp" 27 #include "logging/log.hpp" 28 #include "logging/logStream.hpp" 29 #include "jfr/jfrEvents.hpp" 30 #include "memory/allocation.inline.hpp" 31 #include "memory/metaspaceShared.hpp" 32 #include "memory/padded.hpp" 33 #include "memory/resourceArea.hpp" 34 #include "memory/universe.hpp" 35 #include "oops/markWord.hpp" 36 #include "oops/oop.inline.hpp" 37 #include "runtime/atomic.hpp" 38 #include "runtime/biasedLocking.hpp" 39 #include "runtime/handles.inline.hpp" 40 #include "runtime/handshake.hpp" 41 #include "runtime/interfaceSupport.inline.hpp" 42 #include "runtime/mutexLocker.hpp" 43 #include "runtime/objectMonitor.hpp" 44 #include "runtime/objectMonitor.inline.hpp" 45 #include "runtime/osThread.hpp" 46 #include "runtime/safepointMechanism.inline.hpp" 47 #include "runtime/safepointVerifiers.hpp" 48 #include "runtime/sharedRuntime.hpp" 49 #include "runtime/stubRoutines.hpp" 50 #include "runtime/synchronizer.hpp" 51 #include "runtime/thread.inline.hpp" 52 #include "runtime/timer.hpp" 53 #include "runtime/vframe.hpp" 54 #include "runtime/vmThread.hpp" 55 #include "utilities/align.hpp" 56 #include "utilities/dtrace.hpp" 57 #include "utilities/events.hpp" 58 #include "utilities/preserveException.hpp" 59 60 // The "core" versions of monitor enter and exit reside in this file. 61 // The interpreter and compilers contain specialized transliterated 62 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(), 63 // for instance. If you make changes here, make sure to modify the 64 // interpreter, and both C1 and C2 fast-path inline locking code emission. 65 // 66 // ----------------------------------------------------------------------------- 67 68 #ifdef DTRACE_ENABLED 69 70 // Only bother with this argument setup if dtrace is available 71 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 72 73 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 74 char* bytes = NULL; \ 75 int len = 0; \ 76 jlong jtid = SharedRuntime::get_java_tid(thread); \ 77 Symbol* klassname = ((oop)(obj))->klass()->name(); \ 78 if (klassname != NULL) { \ 79 bytes = (char*)klassname->bytes(); \ 80 len = klassname->utf8_length(); \ 81 } 82 83 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 84 { \ 85 if (DTraceMonitorProbes) { \ 86 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 87 HOTSPOT_MONITOR_WAIT(jtid, \ 88 (uintptr_t)(monitor), bytes, len, (millis)); \ 89 } \ 90 } 91 92 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY 93 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL 94 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED 95 96 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 97 { \ 98 if (DTraceMonitorProbes) { \ 99 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 100 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 101 (uintptr_t)(monitor), bytes, len); \ 102 } \ 103 } 104 105 #else // ndef DTRACE_ENABLED 106 107 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 108 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 109 110 #endif // ndef DTRACE_ENABLED 111 112 // This exists only as a workaround of dtrace bug 6254741 113 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { 114 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 115 return 0; 116 } 117 118 #define NINFLATIONLOCKS 256 119 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS]; 120 121 // global list of blocks of monitors 122 PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL; 123 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false; 124 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false; 125 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0; 126 127 struct ObjectMonitorListGlobals { 128 char _pad_prefix[OM_CACHE_LINE_SIZE]; 129 // These are highly shared list related variables. 130 // To avoid false-sharing they need to be the sole occupants of a cache line. 131 132 // Global ObjectMonitor free list. Newly allocated and deflated 133 // ObjectMonitors are prepended here. 134 ObjectMonitor* _free_list; 135 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*)); 136 137 // Global ObjectMonitor in-use list. When a JavaThread is exiting, 138 // ObjectMonitors on its per-thread in-use list are prepended here. 139 ObjectMonitor* _in_use_list; 140 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*)); 141 142 // Global ObjectMonitor wait list. Deflated ObjectMonitors wait on 143 // this list until after a handshake or a safepoint for platforms 144 // that don't support handshakes. After the handshake or safepoint, 145 // the deflated ObjectMonitors are prepended to free_list. 146 ObjectMonitor* _wait_list; 147 DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*)); 148 149 int _free_count; // # on free_list 150 DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int)); 151 152 int _in_use_count; // # on in_use_list 153 DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int)); 154 155 int _population; // # Extant -- in circulation 156 DEFINE_PAD_MINUS_SIZE(6, OM_CACHE_LINE_SIZE, sizeof(int)); 157 158 int _wait_count; // # on wait_list 159 DEFINE_PAD_MINUS_SIZE(7, OM_CACHE_LINE_SIZE, sizeof(int)); 160 }; 161 static ObjectMonitorListGlobals om_list_globals; 162 163 #define CHAINMARKER (cast_to_oop<intptr_t>(-1)) 164 165 166 // =====================> Spin-lock functions 167 168 // ObjectMonitors are not lockable outside of this file. We use spin-locks 169 // implemented using a bit in the _next_om field instead of the heavier 170 // weight locking mechanisms for faster list management. 171 172 #define OM_LOCK_BIT 0x1 173 174 // Return true if the ObjectMonitor is locked. 175 // Otherwise returns false. 176 static bool is_locked(ObjectMonitor* om) { 177 return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT; 178 } 179 180 // Mark an ObjectMonitor* with OM_LOCK_BIT and return it. 181 static ObjectMonitor* mark_om_ptr(ObjectMonitor* om) { 182 return (ObjectMonitor*)((intptr_t)om | OM_LOCK_BIT); 183 } 184 185 // Return the unmarked next field in an ObjectMonitor. Note: the next 186 // field may or may not have been marked with OM_LOCK_BIT originally. 187 static ObjectMonitor* unmarked_next(ObjectMonitor* om) { 188 return (ObjectMonitor*)((intptr_t)om->next_om() & ~OM_LOCK_BIT); 189 } 190 191 // Try to lock an ObjectMonitor. Returns true if locking was successful. 192 // Otherwise returns false. 193 static bool try_om_lock(ObjectMonitor* om) { 194 // Get current next field without any OM_LOCK_BIT value. 195 ObjectMonitor* next = unmarked_next(om); 196 if (om->try_set_next_om(next, mark_om_ptr(next)) != next) { 197 return false; // Cannot lock the ObjectMonitor. 198 } 199 return true; 200 } 201 202 // Lock an ObjectMonitor. 203 static void om_lock(ObjectMonitor* om) { 204 while (true) { 205 if (try_om_lock(om)) { 206 return; 207 } 208 } 209 } 210 211 // Unlock an ObjectMonitor. 212 static void om_unlock(ObjectMonitor* om) { 213 ObjectMonitor* next = om->next_om(); 214 guarantee(((intptr_t)next & OM_LOCK_BIT) == OM_LOCK_BIT, "next=" INTPTR_FORMAT 215 " must have OM_LOCK_BIT=%x set.", p2i(next), OM_LOCK_BIT); 216 217 next = (ObjectMonitor*)((intptr_t)next & ~OM_LOCK_BIT); // Clear OM_LOCK_BIT. 218 om->set_next_om(next); 219 } 220 221 // Get the list head after locking it. Returns the list head or NULL 222 // if the list is empty. 223 static ObjectMonitor* get_list_head_locked(ObjectMonitor** list_p) { 224 while (true) { 225 ObjectMonitor* mid = Atomic::load(list_p); 226 if (mid == NULL) { 227 return NULL; // The list is empty. 228 } 229 if (try_om_lock(mid)) { 230 if (Atomic::load(list_p) != mid) { 231 // The list head changed before we could lock it so we have to retry. 232 om_unlock(mid); 233 continue; 234 } 235 return mid; 236 } 237 } 238 } 239 240 #undef OM_LOCK_BIT 241 242 243 // =====================> List Management functions 244 245 // Prepend a list of ObjectMonitors to the specified *list_p. 'tail' is 246 // the last ObjectMonitor in the list and there are 'count' on the list. 247 // Also updates the specified *count_p. 248 static void prepend_list_to_common(ObjectMonitor* list, ObjectMonitor* tail, 249 int count, ObjectMonitor** list_p, 250 int* count_p) { 251 while (true) { 252 ObjectMonitor* cur = Atomic::load(list_p); 253 // Prepend list to *list_p. 254 if (!try_om_lock(tail)) { 255 // Failed to lock tail due to a list walker so try it all again. 256 continue; 257 } 258 tail->set_next_om(cur); // tail now points to cur (and unlocks tail) 259 if (cur == NULL) { 260 // No potential race with takers or other prependers since 261 // *list_p is empty. 262 if (Atomic::cmpxchg(list_p, cur, list) == cur) { 263 // Successfully switched *list_p to the list value. 264 Atomic::add(count_p, count); 265 break; 266 } 267 // Implied else: try it all again 268 } else { 269 if (!try_om_lock(cur)) { 270 continue; // failed to lock cur so try it all again 271 } 272 // We locked cur so try to switch *list_p to the list value. 273 if (Atomic::cmpxchg(list_p, cur, list) != cur) { 274 // The list head has changed so unlock cur and try again: 275 om_unlock(cur); 276 continue; 277 } 278 Atomic::add(count_p, count); 279 om_unlock(cur); 280 break; 281 } 282 } 283 } 284 285 // Prepend a newly allocated block of ObjectMonitors to g_block_list and 286 // om_list_globals._free_list. Also updates om_list_globals._population 287 // and om_list_globals._free_count. 288 void ObjectSynchronizer::prepend_block_to_lists(PaddedObjectMonitor* new_blk) { 289 // First we handle g_block_list: 290 while (true) { 291 PaddedObjectMonitor* cur = Atomic::load(&g_block_list); 292 // Prepend new_blk to g_block_list. The first ObjectMonitor in 293 // a block is reserved for use as linkage to the next block. 294 new_blk[0].set_next_om(cur); 295 if (Atomic::cmpxchg(&g_block_list, cur, new_blk) == cur) { 296 // Successfully switched g_block_list to the new_blk value. 297 Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1); 298 break; 299 } 300 // Implied else: try it all again 301 } 302 303 // Second we handle om_list_globals._free_list: 304 prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1, 305 &om_list_globals._free_list, &om_list_globals._free_count); 306 } 307 308 // Prepend a list of ObjectMonitors to om_list_globals._free_list. 309 // 'tail' is the last ObjectMonitor in the list and there are 'count' 310 // on the list. Also updates om_list_globals._free_count. 311 static void prepend_list_to_global_free_list(ObjectMonitor* list, 312 ObjectMonitor* tail, int count) { 313 prepend_list_to_common(list, tail, count, &om_list_globals._free_list, 314 &om_list_globals._free_count); 315 } 316 317 // Prepend a list of ObjectMonitors to om_list_globals._wait_list. 318 // 'tail' is the last ObjectMonitor in the list and there are 'count' 319 // on the list. Also updates om_list_globals._wait_count. 320 static void prepend_list_to_global_wait_list(ObjectMonitor* list, 321 ObjectMonitor* tail, int count) { 322 prepend_list_to_common(list, tail, count, &om_list_globals._wait_list, 323 &om_list_globals._wait_count); 324 } 325 326 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list. 327 // 'tail' is the last ObjectMonitor in the list and there are 'count' 328 // on the list. Also updates om_list_globals._in_use_list. 329 static void prepend_list_to_global_in_use_list(ObjectMonitor* list, 330 ObjectMonitor* tail, int count) { 331 prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list, 332 &om_list_globals._in_use_count); 333 } 334 335 // Prepend an ObjectMonitor to the specified list. Also updates 336 // the specified counter. 337 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p, 338 int* count_p) { 339 while (true) { 340 om_lock(m); // Lock m so we can safely update its next field. 341 ObjectMonitor* cur = NULL; 342 // Lock the list head to guard against races with a list walker 343 // or async deflater thread (which only races in om_in_use_list): 344 if ((cur = get_list_head_locked(list_p)) != NULL) { 345 // List head is now locked so we can safely switch it. 346 m->set_next_om(cur); // m now points to cur (and unlocks m) 347 Atomic::store(list_p, m); // Switch list head to unlocked m. 348 om_unlock(cur); 349 break; 350 } 351 // The list is empty so try to set the list head. 352 assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur)); 353 m->set_next_om(cur); // m now points to NULL (and unlocks m) 354 if (Atomic::cmpxchg(list_p, cur, m) == cur) { 355 // List head is now unlocked m. 356 break; 357 } 358 // Implied else: try it all again 359 } 360 Atomic::inc(count_p); 361 } 362 363 // Prepend an ObjectMonitor to a per-thread om_free_list. 364 // Also updates the per-thread om_free_count. 365 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) { 366 prepend_to_common(m, &self->om_free_list, &self->om_free_count); 367 } 368 369 // Prepend an ObjectMonitor to a per-thread om_in_use_list. 370 // Also updates the per-thread om_in_use_count. 371 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) { 372 prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count); 373 } 374 375 // Take an ObjectMonitor from the start of the specified list. Also 376 // decrements the specified counter. Returns NULL if none are available. 377 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p, 378 int* count_p) { 379 ObjectMonitor* take = NULL; 380 // Lock the list head to guard against races with a list walker 381 // or async deflater thread (which only races in om_list_globals._free_list): 382 if ((take = get_list_head_locked(list_p)) == NULL) { 383 return NULL; // None are available. 384 } 385 ObjectMonitor* next = unmarked_next(take); 386 // Switch locked list head to next (which unlocks the list head, but 387 // leaves take locked): 388 Atomic::store(list_p, next); 389 Atomic::dec(count_p); 390 // Unlock take, but leave the next value for any lagging list 391 // walkers. It will get cleaned up when take is prepended to 392 // the in-use list: 393 om_unlock(take); 394 return take; 395 } 396 397 // Take an ObjectMonitor from the start of the om_list_globals._free_list. 398 // Also updates om_list_globals._free_count. Returns NULL if none are 399 // available. 400 static ObjectMonitor* take_from_start_of_global_free_list() { 401 return take_from_start_of_common(&om_list_globals._free_list, 402 &om_list_globals._free_count); 403 } 404 405 // Take an ObjectMonitor from the start of a per-thread free-list. 406 // Also updates om_free_count. Returns NULL if none are available. 407 static ObjectMonitor* take_from_start_of_om_free_list(Thread* self) { 408 return take_from_start_of_common(&self->om_free_list, &self->om_free_count); 409 } 410 411 412 // =====================> Quick functions 413 414 // The quick_* forms are special fast-path variants used to improve 415 // performance. In the simplest case, a "quick_*" implementation could 416 // simply return false, in which case the caller will perform the necessary 417 // state transitions and call the slow-path form. 418 // The fast-path is designed to handle frequently arising cases in an efficient 419 // manner and is just a degenerate "optimistic" variant of the slow-path. 420 // returns true -- to indicate the call was satisfied. 421 // returns false -- to indicate the call needs the services of the slow-path. 422 // A no-loitering ordinance is in effect for code in the quick_* family 423 // operators: safepoints or indefinite blocking (blocking that might span a 424 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 425 // entry. 426 // 427 // Consider: An interesting optimization is to have the JIT recognize the 428 // following common idiom: 429 // synchronized (someobj) { .... ; notify(); } 430 // That is, we find a notify() or notifyAll() call that immediately precedes 431 // the monitorexit operation. In that case the JIT could fuse the operations 432 // into a single notifyAndExit() runtime primitive. 433 434 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) { 435 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 436 assert(self->is_Java_thread(), "invariant"); 437 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant"); 438 NoSafepointVerifier nsv; 439 if (obj == NULL) return false; // slow-path for invalid obj 440 const markWord mark = obj->mark(); 441 442 if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) { 443 // Degenerate notify 444 // stack-locked by caller so by definition the implied waitset is empty. 445 return true; 446 } 447 448 if (mark.has_monitor()) { 449 ObjectMonitor* const mon = mark.monitor(); 450 assert(mon->object() == obj, "invariant"); 451 if (mon->owner() != self) return false; // slow-path for IMS exception 452 453 if (mon->first_waiter() != NULL) { 454 // We have one or more waiters. Since this is an inflated monitor 455 // that we own, we can transfer one or more threads from the waitset 456 // to the entrylist here and now, avoiding the slow-path. 457 if (all) { 458 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self); 459 } else { 460 DTRACE_MONITOR_PROBE(notify, mon, obj, self); 461 } 462 int free_count = 0; 463 do { 464 mon->INotify(self); 465 ++free_count; 466 } while (mon->first_waiter() != NULL && all); 467 OM_PERFDATA_OP(Notifications, inc(free_count)); 468 } 469 return true; 470 } 471 472 // biased locking and any other IMS exception states take the slow-path 473 return false; 474 } 475 476 477 // The LockNode emitted directly at the synchronization site would have 478 // been too big if it were to have included support for the cases of inflated 479 // recursive enter and exit, so they go here instead. 480 // Note that we can't safely call AsyncPrintJavaStack() from within 481 // quick_enter() as our thread state remains _in_Java. 482 483 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self, 484 BasicLock * lock) { 485 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 486 assert(self->is_Java_thread(), "invariant"); 487 assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant"); 488 NoSafepointVerifier nsv; 489 if (obj == NULL) return false; // Need to throw NPE 490 491 while (true) { 492 const markWord mark = obj->mark(); 493 494 if (mark.has_monitor()) { 495 ObjectMonitorHandle omh; 496 if (!omh.save_om_ptr(obj, mark)) { 497 // Lost a race with async deflation so try again. 498 assert(AsyncDeflateIdleMonitors, "sanity check"); 499 continue; 500 } 501 ObjectMonitor* const m = omh.om_ptr(); 502 assert(m->object() == obj, "invariant"); 503 Thread* const owner = (Thread *) m->_owner; 504 505 // Lock contention and Transactional Lock Elision (TLE) diagnostics 506 // and observability 507 // Case: light contention possibly amenable to TLE 508 // Case: TLE inimical operations such as nested/recursive synchronization 509 510 if (owner == self) { 511 m->_recursions++; 512 return true; 513 } 514 515 // This Java Monitor is inflated so obj's header will never be 516 // displaced to this thread's BasicLock. Make the displaced header 517 // non-NULL so this BasicLock is not seen as recursive nor as 518 // being locked. We do this unconditionally so that this thread's 519 // BasicLock cannot be mis-interpreted by any stack walkers. For 520 // performance reasons, stack walkers generally first check for 521 // Biased Locking in the object's header, the second check is for 522 // stack-locking in the object's header, the third check is for 523 // recursive stack-locking in the displaced header in the BasicLock, 524 // and last are the inflated Java Monitor (ObjectMonitor) checks. 525 lock->set_displaced_header(markWord::unused_mark()); 526 527 if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) { 528 assert(m->_recursions == 0, "invariant"); 529 return true; 530 } 531 532 if (AsyncDeflateIdleMonitors && 533 m->try_set_owner_from(DEFLATER_MARKER, self) == DEFLATER_MARKER) { 534 // The deflation protocol finished the first part (setting owner), 535 // but it failed the second part (making ref_count negative) and 536 // bailed. Acquired the monitor. 537 assert(m->_recursions == 0, "invariant"); 538 return true; 539 } 540 } 541 break; 542 } 543 544 // Note that we could inflate in quick_enter. 545 // This is likely a useful optimization 546 // Critically, in quick_enter() we must not: 547 // -- perform bias revocation, or 548 // -- block indefinitely, or 549 // -- reach a safepoint 550 551 return false; // revert to slow-path 552 } 553 554 // ----------------------------------------------------------------------------- 555 // Monitor Enter/Exit 556 // The interpreter and compiler assembly code tries to lock using the fast path 557 // of this algorithm. Make sure to update that code if the following function is 558 // changed. The implementation is extremely sensitive to race condition. Be careful. 559 560 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) { 561 if (UseBiasedLocking) { 562 if (!SafepointSynchronize::is_at_safepoint()) { 563 BiasedLocking::revoke(obj, THREAD); 564 } else { 565 BiasedLocking::revoke_at_safepoint(obj); 566 } 567 } 568 569 markWord mark = obj->mark(); 570 assert(!mark.has_bias_pattern(), "should not see bias pattern here"); 571 572 if (mark.is_neutral()) { 573 // Anticipate successful CAS -- the ST of the displaced mark must 574 // be visible <= the ST performed by the CAS. 575 lock->set_displaced_header(mark); 576 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 577 return; 578 } 579 // Fall through to inflate() ... 580 } else if (mark.has_locker() && 581 THREAD->is_lock_owned((address)mark.locker())) { 582 assert(lock != mark.locker(), "must not re-lock the same lock"); 583 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock"); 584 lock->set_displaced_header(markWord::from_pointer(NULL)); 585 return; 586 } 587 588 // The object header will never be displaced to this lock, 589 // so it does not matter what the value is, except that it 590 // must be non-zero to avoid looking like a re-entrant lock, 591 // and must not look locked either. 592 lock->set_displaced_header(markWord::unused_mark()); 593 ObjectMonitorHandle omh; 594 inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter); 595 omh.om_ptr()->enter(THREAD); 596 } 597 598 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) { 599 markWord mark = object->mark(); 600 // We cannot check for Biased Locking if we are racing an inflation. 601 assert(mark == markWord::INFLATING() || 602 !mark.has_bias_pattern(), "should not see bias pattern here"); 603 604 markWord dhw = lock->displaced_header(); 605 if (dhw.value() == 0) { 606 // If the displaced header is NULL, then this exit matches up with 607 // a recursive enter. No real work to do here except for diagnostics. 608 #ifndef PRODUCT 609 if (mark != markWord::INFLATING()) { 610 // Only do diagnostics if we are not racing an inflation. Simply 611 // exiting a recursive enter of a Java Monitor that is being 612 // inflated is safe; see the has_monitor() comment below. 613 assert(!mark.is_neutral(), "invariant"); 614 assert(!mark.has_locker() || 615 THREAD->is_lock_owned((address)mark.locker()), "invariant"); 616 if (mark.has_monitor()) { 617 // The BasicLock's displaced_header is marked as a recursive 618 // enter and we have an inflated Java Monitor (ObjectMonitor). 619 // This is a special case where the Java Monitor was inflated 620 // after this thread entered the stack-lock recursively. When a 621 // Java Monitor is inflated, we cannot safely walk the Java 622 // Monitor owner's stack and update the BasicLocks because a 623 // Java Monitor can be asynchronously inflated by a thread that 624 // does not own the Java Monitor. 625 ObjectMonitor* m = mark.monitor(); 626 assert(((oop)(m->object()))->mark() == mark, "invariant"); 627 assert(m->is_entered(THREAD), "invariant"); 628 } 629 } 630 #endif 631 return; 632 } 633 634 if (mark == markWord::from_pointer(lock)) { 635 // If the object is stack-locked by the current thread, try to 636 // swing the displaced header from the BasicLock back to the mark. 637 assert(dhw.is_neutral(), "invariant"); 638 if (object->cas_set_mark(dhw, mark) == mark) { 639 return; 640 } 641 } 642 643 // We have to take the slow-path of possible inflation and then exit. 644 ObjectMonitorHandle omh; 645 inflate(&omh, THREAD, object, inflate_cause_vm_internal); 646 omh.om_ptr()->exit(true, THREAD); 647 } 648 649 // ----------------------------------------------------------------------------- 650 // Class Loader support to workaround deadlocks on the class loader lock objects 651 // Also used by GC 652 // complete_exit()/reenter() are used to wait on a nested lock 653 // i.e. to give up an outer lock completely and then re-enter 654 // Used when holding nested locks - lock acquisition order: lock1 then lock2 655 // 1) complete_exit lock1 - saving recursion count 656 // 2) wait on lock2 657 // 3) when notified on lock2, unlock lock2 658 // 4) reenter lock1 with original recursion count 659 // 5) lock lock2 660 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 661 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { 662 if (UseBiasedLocking) { 663 BiasedLocking::revoke(obj, THREAD); 664 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 665 } 666 667 ObjectMonitorHandle omh; 668 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal); 669 intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD); 670 return ret_code; 671 } 672 673 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 674 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) { 675 if (UseBiasedLocking) { 676 BiasedLocking::revoke(obj, THREAD); 677 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 678 } 679 680 ObjectMonitorHandle omh; 681 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal); 682 omh.om_ptr()->reenter(recursions, THREAD); 683 } 684 // ----------------------------------------------------------------------------- 685 // JNI locks on java objects 686 // NOTE: must use heavy weight monitor to handle jni monitor enter 687 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { 688 // the current locking is from JNI instead of Java code 689 if (UseBiasedLocking) { 690 BiasedLocking::revoke(obj, THREAD); 691 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 692 } 693 THREAD->set_current_pending_monitor_is_from_java(false); 694 ObjectMonitorHandle omh; 695 inflate(&omh, THREAD, obj(), inflate_cause_jni_enter); 696 omh.om_ptr()->enter(THREAD); 697 THREAD->set_current_pending_monitor_is_from_java(true); 698 } 699 700 // NOTE: must use heavy weight monitor to handle jni monitor exit 701 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { 702 if (UseBiasedLocking) { 703 Handle h_obj(THREAD, obj); 704 BiasedLocking::revoke(h_obj, THREAD); 705 obj = h_obj(); 706 } 707 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 708 709 ObjectMonitorHandle omh; 710 inflate(&omh, THREAD, obj, inflate_cause_jni_exit); 711 ObjectMonitor* monitor = omh.om_ptr(); 712 // If this thread has locked the object, exit the monitor. We 713 // intentionally do not use CHECK here because we must exit the 714 // monitor even if an exception is pending. 715 if (monitor->check_owner(THREAD)) { 716 monitor->exit(true, THREAD); 717 } 718 } 719 720 // ----------------------------------------------------------------------------- 721 // Internal VM locks on java objects 722 // standard constructor, allows locking failures 723 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) { 724 _dolock = do_lock; 725 _thread = thread; 726 _thread->check_for_valid_safepoint_state(); 727 _obj = obj; 728 729 if (_dolock) { 730 ObjectSynchronizer::enter(_obj, &_lock, _thread); 731 } 732 } 733 734 ObjectLocker::~ObjectLocker() { 735 if (_dolock) { 736 ObjectSynchronizer::exit(_obj(), &_lock, _thread); 737 } 738 } 739 740 741 // ----------------------------------------------------------------------------- 742 // Wait/Notify/NotifyAll 743 // NOTE: must use heavy weight monitor to handle wait() 744 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 745 if (UseBiasedLocking) { 746 BiasedLocking::revoke(obj, THREAD); 747 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 748 } 749 if (millis < 0) { 750 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 751 } 752 ObjectMonitorHandle omh; 753 inflate(&omh, THREAD, obj(), inflate_cause_wait); 754 ObjectMonitor* monitor = omh.om_ptr(); 755 756 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); 757 monitor->wait(millis, true, THREAD); 758 759 // This dummy call is in place to get around dtrace bug 6254741. Once 760 // that's fixed we can uncomment the following line, remove the call 761 // and change this function back into a "void" func. 762 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 763 int ret_code = dtrace_waited_probe(monitor, obj, THREAD); 764 return ret_code; 765 } 766 767 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) { 768 if (UseBiasedLocking) { 769 BiasedLocking::revoke(obj, THREAD); 770 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 771 } 772 if (millis < 0) { 773 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 774 } 775 ObjectMonitorHandle omh; 776 inflate(&omh, THREAD, obj(), inflate_cause_wait); 777 omh.om_ptr()->wait(millis, false, THREAD); 778 } 779 780 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 781 if (UseBiasedLocking) { 782 BiasedLocking::revoke(obj, THREAD); 783 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 784 } 785 786 markWord mark = obj->mark(); 787 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) { 788 return; 789 } 790 ObjectMonitorHandle omh; 791 inflate(&omh, THREAD, obj(), inflate_cause_notify); 792 omh.om_ptr()->notify(THREAD); 793 } 794 795 // NOTE: see comment of notify() 796 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 797 if (UseBiasedLocking) { 798 BiasedLocking::revoke(obj, THREAD); 799 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 800 } 801 802 markWord mark = obj->mark(); 803 if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) { 804 return; 805 } 806 ObjectMonitorHandle omh; 807 inflate(&omh, THREAD, obj(), inflate_cause_notify); 808 omh.om_ptr()->notifyAll(THREAD); 809 } 810 811 // ----------------------------------------------------------------------------- 812 // Hash Code handling 813 // 814 // Performance concern: 815 // OrderAccess::storestore() calls release() which at one time stored 0 816 // into the global volatile OrderAccess::dummy variable. This store was 817 // unnecessary for correctness. Many threads storing into a common location 818 // causes considerable cache migration or "sloshing" on large SMP systems. 819 // As such, I avoided using OrderAccess::storestore(). In some cases 820 // OrderAccess::fence() -- which incurs local latency on the executing 821 // processor -- is a better choice as it scales on SMP systems. 822 // 823 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for 824 // a discussion of coherency costs. Note that all our current reference 825 // platforms provide strong ST-ST order, so the issue is moot on IA32, 826 // x64, and SPARC. 827 // 828 // As a general policy we use "volatile" to control compiler-based reordering 829 // and explicit fences (barriers) to control for architectural reordering 830 // performed by the CPU(s) or platform. 831 832 struct SharedGlobals { 833 char _pad_prefix[OM_CACHE_LINE_SIZE]; 834 // These are highly shared mostly-read variables. 835 // To avoid false-sharing they need to be the sole occupants of a cache line. 836 volatile int stw_random; 837 volatile int stw_cycle; 838 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int) * 2); 839 // Hot RW variable -- Sequester to avoid false-sharing 840 volatile int hc_sequence; 841 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 842 }; 843 844 static SharedGlobals GVars; 845 static int _forceMonitorScavenge = 0; // Scavenge required and pending 846 847 static markWord read_stable_mark(oop obj) { 848 markWord mark = obj->mark(); 849 if (!mark.is_being_inflated()) { 850 return mark; // normal fast-path return 851 } 852 853 int its = 0; 854 for (;;) { 855 markWord mark = obj->mark(); 856 if (!mark.is_being_inflated()) { 857 return mark; // normal fast-path return 858 } 859 860 // The object is being inflated by some other thread. 861 // The caller of read_stable_mark() must wait for inflation to complete. 862 // Avoid live-lock 863 // TODO: consider calling SafepointSynchronize::do_call_back() while 864 // spinning to see if there's a safepoint pending. If so, immediately 865 // yielding or blocking would be appropriate. Avoid spinning while 866 // there is a safepoint pending. 867 // TODO: add inflation contention performance counters. 868 // TODO: restrict the aggregate number of spinners. 869 870 ++its; 871 if (its > 10000 || !os::is_MP()) { 872 if (its & 1) { 873 os::naked_yield(); 874 } else { 875 // Note that the following code attenuates the livelock problem but is not 876 // a complete remedy. A more complete solution would require that the inflating 877 // thread hold the associated inflation lock. The following code simply restricts 878 // the number of spinners to at most one. We'll have N-2 threads blocked 879 // on the inflationlock, 1 thread holding the inflation lock and using 880 // a yield/park strategy, and 1 thread in the midst of inflation. 881 // A more refined approach would be to change the encoding of INFLATING 882 // to allow encapsulation of a native thread pointer. Threads waiting for 883 // inflation to complete would use CAS to push themselves onto a singly linked 884 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 885 // and calling park(). When inflation was complete the thread that accomplished inflation 886 // would detach the list and set the markword to inflated with a single CAS and 887 // then for each thread on the list, set the flag and unpark() the thread. 888 // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease 889 // wakes at most one thread whereas we need to wake the entire list. 890 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1); 891 int YieldThenBlock = 0; 892 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant"); 893 assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant"); 894 Thread::muxAcquire(gInflationLocks + ix, "gInflationLock"); 895 while (obj->mark() == markWord::INFLATING()) { 896 // Beware: NakedYield() is advisory and has almost no effect on some platforms 897 // so we periodically call self->_ParkEvent->park(1). 898 // We use a mixed spin/yield/block mechanism. 899 if ((YieldThenBlock++) >= 16) { 900 Thread::current()->_ParkEvent->park(1); 901 } else { 902 os::naked_yield(); 903 } 904 } 905 Thread::muxRelease(gInflationLocks + ix); 906 } 907 } else { 908 SpinPause(); // SMP-polite spinning 909 } 910 } 911 } 912 913 // hashCode() generation : 914 // 915 // Possibilities: 916 // * MD5Digest of {obj,stw_random} 917 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function. 918 // * A DES- or AES-style SBox[] mechanism 919 // * One of the Phi-based schemes, such as: 920 // 2654435761 = 2^32 * Phi (golden ratio) 921 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ; 922 // * A variation of Marsaglia's shift-xor RNG scheme. 923 // * (obj ^ stw_random) is appealing, but can result 924 // in undesirable regularity in the hashCode values of adjacent objects 925 // (objects allocated back-to-back, in particular). This could potentially 926 // result in hashtable collisions and reduced hashtable efficiency. 927 // There are simple ways to "diffuse" the middle address bits over the 928 // generated hashCode values: 929 930 static inline intptr_t get_next_hash(Thread* self, oop obj) { 931 intptr_t value = 0; 932 if (hashCode == 0) { 933 // This form uses global Park-Miller RNG. 934 // On MP system we'll have lots of RW access to a global, so the 935 // mechanism induces lots of coherency traffic. 936 value = os::random(); 937 } else if (hashCode == 1) { 938 // This variation has the property of being stable (idempotent) 939 // between STW operations. This can be useful in some of the 1-0 940 // synchronization schemes. 941 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3; 942 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random; 943 } else if (hashCode == 2) { 944 value = 1; // for sensitivity testing 945 } else if (hashCode == 3) { 946 value = ++GVars.hc_sequence; 947 } else if (hashCode == 4) { 948 value = cast_from_oop<intptr_t>(obj); 949 } else { 950 // Marsaglia's xor-shift scheme with thread-specific state 951 // This is probably the best overall implementation -- we'll 952 // likely make this the default in future releases. 953 unsigned t = self->_hashStateX; 954 t ^= (t << 11); 955 self->_hashStateX = self->_hashStateY; 956 self->_hashStateY = self->_hashStateZ; 957 self->_hashStateZ = self->_hashStateW; 958 unsigned v = self->_hashStateW; 959 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 960 self->_hashStateW = v; 961 value = v; 962 } 963 964 value &= markWord::hash_mask; 965 if (value == 0) value = 0xBAD; 966 assert(value != markWord::no_hash, "invariant"); 967 return value; 968 } 969 970 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) { 971 if (UseBiasedLocking) { 972 // NOTE: many places throughout the JVM do not expect a safepoint 973 // to be taken here, in particular most operations on perm gen 974 // objects. However, we only ever bias Java instances and all of 975 // the call sites of identity_hash that might revoke biases have 976 // been checked to make sure they can handle a safepoint. The 977 // added check of the bias pattern is to avoid useless calls to 978 // thread-local storage. 979 if (obj->mark().has_bias_pattern()) { 980 // Handle for oop obj in case of STW safepoint 981 Handle hobj(self, obj); 982 // Relaxing assertion for bug 6320749. 983 assert(Universe::verify_in_progress() || 984 !SafepointSynchronize::is_at_safepoint(), 985 "biases should not be seen by VM thread here"); 986 BiasedLocking::revoke(hobj, JavaThread::current()); 987 obj = hobj(); 988 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now"); 989 } 990 } 991 992 // hashCode() is a heap mutator ... 993 // Relaxing assertion for bug 6320749. 994 assert(Universe::verify_in_progress() || DumpSharedSpaces || 995 !SafepointSynchronize::is_at_safepoint(), "invariant"); 996 assert(Universe::verify_in_progress() || DumpSharedSpaces || 997 self->is_Java_thread() , "invariant"); 998 assert(Universe::verify_in_progress() || DumpSharedSpaces || 999 ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant"); 1000 1001 while (true) { 1002 ObjectMonitor* monitor = NULL; 1003 markWord temp, test; 1004 intptr_t hash; 1005 markWord mark = read_stable_mark(obj); 1006 1007 // object should remain ineligible for biased locking 1008 assert(!mark.has_bias_pattern(), "invariant"); 1009 1010 if (mark.is_neutral()) { // if this is a normal header 1011 hash = mark.hash(); 1012 if (hash != 0) { // if it has a hash, just return it 1013 return hash; 1014 } 1015 hash = get_next_hash(self, obj); // get a new hash 1016 temp = mark.copy_set_hash(hash); // merge the hash into header 1017 // try to install the hash 1018 test = obj->cas_set_mark(temp, mark); 1019 if (test == mark) { // if the hash was installed, return it 1020 return hash; 1021 } 1022 // Failed to install the hash. It could be that another thread 1023 // installed the hash just before our attempt or inflation has 1024 // occurred or... so we fall thru to inflate the monitor for 1025 // stability and then install the hash. 1026 } else if (mark.has_monitor()) { 1027 ObjectMonitorHandle omh; 1028 if (!omh.save_om_ptr(obj, mark)) { 1029 // Lost a race with async deflation so try again. 1030 assert(AsyncDeflateIdleMonitors, "sanity check"); 1031 continue; 1032 } 1033 monitor = omh.om_ptr(); 1034 temp = monitor->header(); 1035 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1036 hash = temp.hash(); 1037 if (hash != 0) { // if it has a hash, just return it 1038 return hash; 1039 } 1040 // Fall thru so we only have one place that installs the hash in 1041 // the ObjectMonitor. 1042 } else if (self->is_lock_owned((address)mark.locker())) { 1043 // This is a stack lock owned by the calling thread so fetch the 1044 // displaced markWord from the BasicLock on the stack. 1045 temp = mark.displaced_mark_helper(); 1046 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1047 hash = temp.hash(); 1048 if (hash != 0) { // if it has a hash, just return it 1049 return hash; 1050 } 1051 // WARNING: 1052 // The displaced header in the BasicLock on a thread's stack 1053 // is strictly immutable. It CANNOT be changed in ANY cases. 1054 // So we have to inflate the stack lock into an ObjectMonitor 1055 // even if the current thread owns the lock. The BasicLock on 1056 // a thread's stack can be asynchronously read by other threads 1057 // during an inflate() call so any change to that stack memory 1058 // may not propagate to other threads correctly. 1059 } 1060 1061 // Inflate the monitor to set the hash. 1062 ObjectMonitorHandle omh; 1063 inflate(&omh, self, obj, inflate_cause_hash_code); 1064 monitor = omh.om_ptr(); 1065 // Load ObjectMonitor's header/dmw field and see if it has a hash. 1066 mark = monitor->header(); 1067 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1068 hash = mark.hash(); 1069 if (hash == 0) { // if it does not have a hash 1070 hash = get_next_hash(self, obj); // get a new hash 1071 temp = mark.copy_set_hash(hash); // merge the hash into header 1072 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1073 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value()); 1074 test = markWord(v); 1075 if (test != mark) { 1076 // The attempt to update the ObjectMonitor's header/dmw field 1077 // did not work. This can happen if another thread managed to 1078 // merge in the hash just before our cmpxchg(). 1079 // If we add any new usages of the header/dmw field, this code 1080 // will need to be updated. 1081 hash = test.hash(); 1082 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 1083 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash"); 1084 } 1085 } 1086 // We finally get the hash. 1087 return hash; 1088 } 1089 } 1090 1091 // Deprecated -- use FastHashCode() instead. 1092 1093 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 1094 return FastHashCode(Thread::current(), obj()); 1095 } 1096 1097 1098 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, 1099 Handle h_obj) { 1100 if (UseBiasedLocking) { 1101 BiasedLocking::revoke(h_obj, thread); 1102 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 1103 } 1104 1105 assert(thread == JavaThread::current(), "Can only be called on current thread"); 1106 oop obj = h_obj(); 1107 1108 while (true) { 1109 markWord mark = read_stable_mark(obj); 1110 1111 // Uncontended case, header points to stack 1112 if (mark.has_locker()) { 1113 return thread->is_lock_owned((address)mark.locker()); 1114 } 1115 // Contended case, header points to ObjectMonitor (tagged pointer) 1116 if (mark.has_monitor()) { 1117 ObjectMonitorHandle omh; 1118 if (!omh.save_om_ptr(obj, mark)) { 1119 // Lost a race with async deflation so try again. 1120 assert(AsyncDeflateIdleMonitors, "sanity check"); 1121 continue; 1122 } 1123 bool ret_code = omh.om_ptr()->is_entered(thread) != 0; 1124 return ret_code; 1125 } 1126 // Unlocked case, header in place 1127 assert(mark.is_neutral(), "sanity check"); 1128 return false; 1129 } 1130 } 1131 1132 // Be aware of this method could revoke bias of the lock object. 1133 // This method queries the ownership of the lock handle specified by 'h_obj'. 1134 // If the current thread owns the lock, it returns owner_self. If no 1135 // thread owns the lock, it returns owner_none. Otherwise, it will return 1136 // owner_other. 1137 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership 1138 (JavaThread *self, Handle h_obj) { 1139 // The caller must beware this method can revoke bias, and 1140 // revocation can result in a safepoint. 1141 assert(!SafepointSynchronize::is_at_safepoint(), "invariant"); 1142 assert(self->thread_state() != _thread_blocked, "invariant"); 1143 1144 // Possible mark states: neutral, biased, stack-locked, inflated 1145 1146 if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) { 1147 // CASE: biased 1148 BiasedLocking::revoke(h_obj, self); 1149 assert(!h_obj->mark().has_bias_pattern(), 1150 "biases should be revoked by now"); 1151 } 1152 1153 assert(self == JavaThread::current(), "Can only be called on current thread"); 1154 oop obj = h_obj(); 1155 1156 while (true) { 1157 markWord mark = read_stable_mark(obj); 1158 1159 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack. 1160 if (mark.has_locker()) { 1161 return self->is_lock_owned((address)mark.locker()) ? 1162 owner_self : owner_other; 1163 } 1164 1165 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor. 1166 // The Object:ObjectMonitor relationship is stable as long as we're 1167 // not at a safepoint and AsyncDeflateIdleMonitors is false. 1168 if (mark.has_monitor()) { 1169 ObjectMonitorHandle omh; 1170 if (!omh.save_om_ptr(obj, mark)) { 1171 // Lost a race with async deflation so try again. 1172 assert(AsyncDeflateIdleMonitors, "sanity check"); 1173 continue; 1174 } 1175 ObjectMonitor* monitor = omh.om_ptr(); 1176 void* owner = monitor->_owner; 1177 if (owner == NULL) return owner_none; 1178 return (owner == self || 1179 self->is_lock_owned((address)owner)) ? owner_self : owner_other; 1180 } 1181 1182 // CASE: neutral 1183 assert(mark.is_neutral(), "sanity check"); 1184 return owner_none; // it's unlocked 1185 } 1186 } 1187 1188 // FIXME: jvmti should call this 1189 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 1190 if (UseBiasedLocking) { 1191 if (SafepointSynchronize::is_at_safepoint()) { 1192 BiasedLocking::revoke_at_safepoint(h_obj); 1193 } else { 1194 BiasedLocking::revoke(h_obj, JavaThread::current()); 1195 } 1196 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now"); 1197 } 1198 1199 oop obj = h_obj(); 1200 1201 while (true) { 1202 address owner = NULL; 1203 markWord mark = read_stable_mark(obj); 1204 1205 // Uncontended case, header points to stack 1206 if (mark.has_locker()) { 1207 owner = (address) mark.locker(); 1208 } 1209 1210 // Contended case, header points to ObjectMonitor (tagged pointer) 1211 else if (mark.has_monitor()) { 1212 ObjectMonitorHandle omh; 1213 if (!omh.save_om_ptr(obj, mark)) { 1214 // Lost a race with async deflation so try again. 1215 assert(AsyncDeflateIdleMonitors, "sanity check"); 1216 continue; 1217 } 1218 ObjectMonitor* monitor = omh.om_ptr(); 1219 assert(monitor != NULL, "monitor should be non-null"); 1220 owner = (address) monitor->owner(); 1221 } 1222 1223 if (owner != NULL) { 1224 // owning_thread_from_monitor_owner() may also return NULL here 1225 return Threads::owning_thread_from_monitor_owner(t_list, owner); 1226 } 1227 1228 // Unlocked case, header in place 1229 // Cannot have assertion since this object may have been 1230 // locked by another thread when reaching here. 1231 // assert(mark.is_neutral(), "sanity check"); 1232 1233 return NULL; 1234 } 1235 } 1236 1237 // Visitors ... 1238 1239 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { 1240 PaddedObjectMonitor* block = Atomic::load(&g_block_list); 1241 while (block != NULL) { 1242 assert(block->object() == CHAINMARKER, "must be a block header"); 1243 for (int i = _BLOCKSIZE - 1; i > 0; i--) { 1244 ObjectMonitor* mid = (ObjectMonitor *)(block + i); 1245 ObjectMonitorHandle omh; 1246 if (!mid->is_free() && omh.save_om_ptr_if_safe(mid)) { 1247 // The ObjectMonitor* is not free and it has been made safe. 1248 if (mid->object() == NULL) { 1249 // Only process with closure if the object is set. 1250 continue; 1251 } 1252 closure->do_monitor(mid); 1253 } 1254 } 1255 // unmarked_next() is not needed with g_block_list (no locking 1256 // used with block linkage _next_om fields). 1257 block = (PaddedObjectMonitor*)block->next_om(); 1258 } 1259 } 1260 1261 static bool monitors_used_above_threshold() { 1262 int population = Atomic::load(&om_list_globals._population); 1263 if (population == 0) { 1264 return false; 1265 } 1266 if (MonitorUsedDeflationThreshold > 0) { 1267 int monitors_used = population - Atomic::load(&om_list_globals._free_count) - 1268 Atomic::load(&om_list_globals._wait_count); 1269 int monitor_usage = (monitors_used * 100LL) / population; 1270 return monitor_usage > MonitorUsedDeflationThreshold; 1271 } 1272 return false; 1273 } 1274 1275 // Returns true if MonitorBound is set (> 0) and if the specified 1276 // cnt is > MonitorBound. Otherwise returns false. 1277 static bool is_MonitorBound_exceeded(const int cnt) { 1278 const int mx = MonitorBound; 1279 return mx > 0 && cnt > mx; 1280 } 1281 1282 bool ObjectSynchronizer::is_async_deflation_needed() { 1283 if (!AsyncDeflateIdleMonitors) { 1284 return false; 1285 } 1286 if (is_async_deflation_requested()) { 1287 // Async deflation request. 1288 return true; 1289 } 1290 if (AsyncDeflationInterval > 0 && 1291 time_since_last_async_deflation_ms() > AsyncDeflationInterval && 1292 monitors_used_above_threshold()) { 1293 // It's been longer than our specified deflate interval and there 1294 // are too many monitors in use. We don't deflate more frequently 1295 // than AsyncDeflationInterval (unless is_async_deflation_requested) 1296 // in order to not swamp the ServiceThread. 1297 _last_async_deflation_time_ns = os::javaTimeNanos(); 1298 return true; 1299 } 1300 int monitors_used = Atomic::load(&om_list_globals._population) - 1301 Atomic::load(&om_list_globals._free_count) - 1302 Atomic::load(&om_list_globals._wait_count); 1303 if (is_MonitorBound_exceeded(monitors_used)) { 1304 // Not enough ObjectMonitors on the global free list. 1305 return true; 1306 } 1307 return false; 1308 } 1309 1310 bool ObjectSynchronizer::needs_monitor_scavenge() { 1311 if (Atomic::load(&_forceMonitorScavenge) == 1) { 1312 log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup."); 1313 return true; 1314 } 1315 return false; 1316 } 1317 1318 bool ObjectSynchronizer::is_safepoint_deflation_needed() { 1319 if (!AsyncDeflateIdleMonitors) { 1320 if (monitors_used_above_threshold()) { 1321 // Too many monitors in use. 1322 return true; 1323 } 1324 return needs_monitor_scavenge(); 1325 } 1326 if (is_special_deflation_requested()) { 1327 // For AsyncDeflateIdleMonitors only do a safepoint deflation 1328 // if there is a special deflation request. 1329 return true; 1330 } 1331 return false; 1332 } 1333 1334 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() { 1335 return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS); 1336 } 1337 1338 void ObjectSynchronizer::oops_do(OopClosure* f) { 1339 // We only scan the global used list here (for moribund threads), and 1340 // the thread-local monitors in Thread::oops_do(). 1341 global_used_oops_do(f); 1342 } 1343 1344 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) { 1345 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1346 list_oops_do(Atomic::load(&om_list_globals._in_use_list), f); 1347 } 1348 1349 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) { 1350 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1351 list_oops_do(thread->om_in_use_list, f); 1352 } 1353 1354 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) { 1355 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 1356 // The oops_do() phase does not overlap with monitor deflation 1357 // so no need to lock ObjectMonitors for the list traversal and 1358 // no need to update the ObjectMonitor's ref_count for this 1359 // ObjectMonitor* use. 1360 for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) { 1361 if (mid->object() != NULL) { 1362 f->do_oop((oop*)mid->object_addr()); 1363 } 1364 } 1365 } 1366 1367 1368 // ----------------------------------------------------------------------------- 1369 // ObjectMonitor Lifecycle 1370 // ----------------------- 1371 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread 1372 // free list and associates them with objects. Deflation -- which occurs at 1373 // STW-time or asynchronously -- disassociates idle monitors from objects. 1374 // Such scavenged monitors are returned to the om_list_globals._free_list. 1375 // 1376 // ObjectMonitors reside in type-stable memory (TSM) and are immortal. 1377 // 1378 // Lifecycle: 1379 // -- unassigned and on the om_list_globals._free_list 1380 // -- unassigned and on a per-thread free list 1381 // -- assigned to an object. The object is inflated and the mark refers 1382 // to the ObjectMonitor. 1383 1384 1385 // Constraining monitor pool growth via MonitorBound ... 1386 // 1387 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled. 1388 // 1389 // When safepoint deflation is being used (!AsyncDeflateIdleMonitors): 1390 // The monitor pool is grow-only. We scavenge at STW safepoint-time, but the 1391 // the rate of scavenging is driven primarily by GC. As such, we can find 1392 // an inordinate number of monitors in circulation. 1393 // To avoid that scenario we can artificially induce a STW safepoint 1394 // if the pool appears to be growing past some reasonable bound. 1395 // Generally we favor time in space-time tradeoffs, but as there's no 1396 // natural back-pressure on the # of extant monitors we need to impose some 1397 // type of limit. Beware that if MonitorBound is set to too low a value 1398 // we could just loop. In addition, if MonitorBound is set to a low value 1399 // we'll incur more safepoints, which are harmful to performance. 1400 // See also: GuaranteedSafepointInterval 1401 // 1402 // When safepoint deflation is being used and MonitorBound is set, the 1403 // boundry applies to 1404 // (om_list_globals._population - om_list_globals._free_count) 1405 // i.e., if there are not enough ObjectMonitors on the global free list, 1406 // then a safepoint deflation is induced. Picking a good MonitorBound value 1407 // is non-trivial. 1408 // 1409 // When async deflation is being used: 1410 // The monitor pool is still grow-only. Async deflation is requested 1411 // by a safepoint's cleanup phase or by the ServiceThread at periodic 1412 // intervals when is_async_deflation_needed() returns true. In 1413 // addition to other policies that are checked, if there are not 1414 // enough ObjectMonitors on the global free list, then 1415 // is_async_deflation_needed() will return true. The ServiceThread 1416 // calls deflate_global_idle_monitors_using_JT() and also calls 1417 // deflate_per_thread_idle_monitors_using_JT() as needed. 1418 1419 static void InduceScavenge(Thread* self, const char * Whence) { 1420 assert(!AsyncDeflateIdleMonitors, "is not used by async deflation"); 1421 1422 // Induce STW safepoint to trim monitors 1423 // Ultimately, this results in a call to deflate_idle_monitors() in the near future. 1424 // More precisely, trigger a cleanup safepoint as the number 1425 // of active monitors passes the specified threshold. 1426 // TODO: assert thread state is reasonable 1427 1428 if (Atomic::xchg(&_forceMonitorScavenge, 1) == 0) { 1429 VMThread::check_for_forced_cleanup(); 1430 } 1431 } 1432 1433 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) { 1434 // A large MAXPRIVATE value reduces both list lock contention 1435 // and list coherency traffic, but also tends to increase the 1436 // number of ObjectMonitors in circulation as well as the STW 1437 // scavenge costs. As usual, we lean toward time in space-time 1438 // tradeoffs. 1439 const int MAXPRIVATE = 1024; 1440 NoSafepointVerifier nsv; 1441 1442 stringStream ss; 1443 for (;;) { 1444 ObjectMonitor* m; 1445 1446 // 1: try to allocate from the thread's local om_free_list. 1447 // Threads will attempt to allocate first from their local list, then 1448 // from the global list, and only after those attempts fail will the 1449 // thread attempt to instantiate new monitors. Thread-local free lists 1450 // improve allocation latency, as well as reducing coherency traffic 1451 // on the shared global list. 1452 m = take_from_start_of_om_free_list(self); 1453 if (m != NULL) { 1454 guarantee(m->object() == NULL, "invariant"); 1455 m->set_allocation_state(ObjectMonitor::New); 1456 prepend_to_om_in_use_list(self, m); 1457 return m; 1458 } 1459 1460 // 2: try to allocate from the global om_list_globals._free_list 1461 // If we're using thread-local free lists then try 1462 // to reprovision the caller's free list. 1463 if (Atomic::load(&om_list_globals._free_list) != NULL) { 1464 // Reprovision the thread's om_free_list. 1465 // Use bulk transfers to reduce the allocation rate and heat 1466 // on various locks. 1467 for (int i = self->om_free_provision; --i >= 0;) { 1468 ObjectMonitor* take = take_from_start_of_global_free_list(); 1469 if (take == NULL) { 1470 break; // No more are available. 1471 } 1472 guarantee(take->object() == NULL, "invariant"); 1473 if (AsyncDeflateIdleMonitors) { 1474 // We allowed 3 field values to linger during async deflation. 1475 // Clear or restore them as appropriate. 1476 take->set_header(markWord::zero()); 1477 // DEFLATER_MARKER is the only non-NULL value we should see here. 1478 take->try_set_owner_from(DEFLATER_MARKER, NULL); 1479 if (take->ref_count() < 0) { 1480 // Add back max_jint to restore the ref_count field to its 1481 // proper value. 1482 Atomic::add(&take->_ref_count, max_jint); 1483 1484 #ifdef ASSERT 1485 jint l_ref_count = take->ref_count(); 1486 #endif 1487 assert(l_ref_count >= 0, "must not be negative: l_ref_count=%d, ref_count=%d", 1488 l_ref_count, take->ref_count()); 1489 } 1490 } 1491 take->Recycle(); 1492 // Since we're taking from the global free-list, take must be Free. 1493 // om_release() also sets the allocation state to Free because it 1494 // is called from other code paths. 1495 assert(take->is_free(), "invariant"); 1496 om_release(self, take, false); 1497 } 1498 self->om_free_provision += 1 + (self->om_free_provision / 2); 1499 if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE; 1500 1501 if (!AsyncDeflateIdleMonitors && 1502 is_MonitorBound_exceeded(Atomic::load(&om_list_globals._population) - 1503 Atomic::load(&om_list_globals._free_count))) { 1504 // Not enough ObjectMonitors on the global free list. 1505 // We can't safely induce a STW safepoint from om_alloc() as our thread 1506 // state may not be appropriate for such activities and callers may hold 1507 // naked oops, so instead we defer the action. 1508 InduceScavenge(self, "om_alloc"); 1509 } 1510 continue; 1511 } 1512 1513 // 3: allocate a block of new ObjectMonitors 1514 // Both the local and global free lists are empty -- resort to malloc(). 1515 // In the current implementation ObjectMonitors are TSM - immortal. 1516 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want 1517 // each ObjectMonitor to start at the beginning of a cache line, 1518 // so we use align_up(). 1519 // A better solution would be to use C++ placement-new. 1520 // BEWARE: As it stands currently, we don't run the ctors! 1521 assert(_BLOCKSIZE > 1, "invariant"); 1522 size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE; 1523 PaddedObjectMonitor* temp; 1524 size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1); 1525 void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal); 1526 temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE); 1527 (void)memset((void *) temp, 0, neededsize); 1528 1529 // Format the block. 1530 // initialize the linked list, each monitor points to its next 1531 // forming the single linked free list, the very first monitor 1532 // will points to next block, which forms the block list. 1533 // The trick of using the 1st element in the block as g_block_list 1534 // linkage should be reconsidered. A better implementation would 1535 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } 1536 1537 for (int i = 1; i < _BLOCKSIZE; i++) { 1538 temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]); 1539 assert(temp[i].is_free(), "invariant"); 1540 } 1541 1542 // terminate the last monitor as the end of list 1543 temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL); 1544 1545 // Element [0] is reserved for global list linkage 1546 temp[0].set_object(CHAINMARKER); 1547 1548 // Consider carving out this thread's current request from the 1549 // block in hand. This avoids some lock traffic and redundant 1550 // list activity. 1551 1552 prepend_block_to_lists(temp); 1553 } 1554 } 1555 1556 // Place "m" on the caller's private per-thread om_free_list. 1557 // In practice there's no need to clamp or limit the number of 1558 // monitors on a thread's om_free_list as the only non-allocation time 1559 // we'll call om_release() is to return a monitor to the free list after 1560 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to 1561 // accumulate on a thread's free list. 1562 // 1563 // Key constraint: all ObjectMonitors on a thread's free list and the global 1564 // free list must have their object field set to null. This prevents the 1565 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT() 1566 // -- from reclaiming them while we are trying to release them. 1567 1568 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m, 1569 bool from_per_thread_alloc) { 1570 guarantee(m->header().value() == 0, "invariant"); 1571 guarantee(m->object() == NULL, "invariant"); 1572 NoSafepointVerifier nsv; 1573 1574 stringStream ss; 1575 guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: " 1576 "%s, recursions=" INTX_FORMAT, m->is_busy_to_string(&ss), 1577 m->_recursions); 1578 m->set_allocation_state(ObjectMonitor::Free); 1579 // _next_om is used for both per-thread in-use and free lists so 1580 // we have to remove 'm' from the in-use list first (as needed). 1581 if (from_per_thread_alloc) { 1582 // Need to remove 'm' from om_in_use_list. 1583 ObjectMonitor* mid = NULL; 1584 ObjectMonitor* next = NULL; 1585 1586 // This list walk can race with another list walker or with async 1587 // deflation so we have to worry about an ObjectMonitor being 1588 // removed from this list while we are walking it. 1589 1590 // Lock the list head to avoid racing with another list walker 1591 // or with async deflation. 1592 if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) { 1593 fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self)); 1594 } 1595 next = unmarked_next(mid); 1596 if (m == mid) { 1597 // First special case: 1598 // 'm' matches mid, is the list head and is locked. Switch the list 1599 // head to next which unlocks the list head, but leaves the extracted 1600 // mid locked: 1601 Atomic::store(&self->om_in_use_list, next); 1602 } else if (m == next) { 1603 // Second special case: 1604 // 'm' matches next after the list head and we already have the list 1605 // head locked so set mid to what we are extracting: 1606 mid = next; 1607 // Lock mid to prevent races with a list walker or an async 1608 // deflater thread that's ahead of us. The locked list head 1609 // prevents races from behind us. 1610 om_lock(mid); 1611 // Update next to what follows mid (if anything): 1612 next = unmarked_next(mid); 1613 // Switch next after the list head to new next which unlocks the 1614 // list head, but leaves the extracted mid locked: 1615 self->om_in_use_list->set_next_om(next); 1616 } else { 1617 // We have to search the list to find 'm'. 1618 guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT 1619 " is too short.", p2i(self), p2i(self->om_in_use_list)); 1620 // Our starting anchor is next after the list head which is the 1621 // last ObjectMonitor we checked: 1622 ObjectMonitor* anchor = next; 1623 // Lock anchor to prevent races with a list walker or an async 1624 // deflater thread that's ahead of us. The locked list head 1625 // prevents races from behind us. 1626 om_lock(anchor); 1627 om_unlock(mid); // Unlock the list head now that anchor is locked. 1628 while ((mid = unmarked_next(anchor)) != NULL) { 1629 if (m == mid) { 1630 // We found 'm' on the per-thread in-use list so extract it. 1631 // Update next to what follows mid (if anything): 1632 next = unmarked_next(mid); 1633 // Switch next after the anchor to new next which unlocks the 1634 // anchor, but leaves the extracted mid locked: 1635 anchor->set_next_om(next); 1636 break; 1637 } else { 1638 // Lock the next anchor to prevent races with a list walker 1639 // or an async deflater thread that's ahead of us. The locked 1640 // current anchor prevents races from behind us. 1641 om_lock(mid); 1642 // Unlock current anchor now that next anchor is locked: 1643 om_unlock(anchor); 1644 anchor = mid; // Advance to new anchor and try again. 1645 } 1646 } 1647 } 1648 1649 if (mid == NULL) { 1650 // Reached end of the list and didn't find 'm' so: 1651 fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list=" 1652 INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list)); 1653 } 1654 1655 // At this point mid is disconnected from the in-use list so 1656 // its lock no longer has any effects on the in-use list. 1657 Atomic::dec(&self->om_in_use_count); 1658 // Unlock mid, but leave the next value for any lagging list 1659 // walkers. It will get cleaned up when mid is prepended to 1660 // the thread's free list: 1661 om_unlock(mid); 1662 } 1663 1664 prepend_to_om_free_list(self, m); 1665 guarantee(m->is_free(), "invariant"); 1666 } 1667 1668 // Return ObjectMonitors on a moribund thread's free and in-use 1669 // lists to the appropriate global lists. The ObjectMonitors on the 1670 // per-thread in-use list may still be in use by other threads. 1671 // 1672 // We currently call om_flush() from Threads::remove() before the 1673 // thread has been excised from the thread list and is no longer a 1674 // mutator. This means that om_flush() cannot run concurrently with 1675 // a safepoint and interleave with deflate_idle_monitors(). In 1676 // particular, this ensures that the thread's in-use monitors are 1677 // scanned by a GC safepoint, either via Thread::oops_do() (before 1678 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after 1679 // om_flush() is called). 1680 // 1681 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT() 1682 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can 1683 // run at the same time as om_flush() so we have to follow a careful 1684 // protocol to prevent list corruption. 1685 1686 void ObjectSynchronizer::om_flush(Thread* self) { 1687 // Process the per-thread in-use list first to be consistent. 1688 int in_use_count = 0; 1689 ObjectMonitor* in_use_list = NULL; 1690 ObjectMonitor* in_use_tail = NULL; 1691 NoSafepointVerifier nsv; 1692 1693 // This function can race with a list walker or with an async 1694 // deflater thread so we lock the list head to prevent confusion. 1695 // An async deflater thread checks to see if the target thread 1696 // is exiting, but if it has made it past that check before we 1697 // started exiting, then it is racing to get to the in-use list. 1698 if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) { 1699 // At this point, we have locked the in-use list head so a racing 1700 // thread cannot come in after us. However, a racing thread could 1701 // be ahead of us; we'll detect that and delay to let it finish. 1702 // 1703 // The thread is going away, however the ObjectMonitors on the 1704 // om_in_use_list may still be in-use by other threads. Link 1705 // them to in_use_tail, which will be linked into the global 1706 // in-use list (om_list_globals._in_use_list) below. 1707 // 1708 // Account for the in-use list head before the loop since it is 1709 // already locked (by this thread): 1710 in_use_tail = in_use_list; 1711 in_use_count++; 1712 for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) { 1713 if (is_locked(cur_om)) { 1714 // cur_om is locked so there must be a racing walker or async 1715 // deflater thread ahead of us so we'll give it a chance to finish. 1716 while (is_locked(cur_om)) { 1717 os::naked_short_sleep(1); 1718 } 1719 // Refetch the possibly changed next field and try again. 1720 cur_om = unmarked_next(in_use_tail); 1721 continue; 1722 } 1723 if (cur_om->is_free()) { 1724 // cur_om was deflated and the allocation state was changed 1725 // to Free while it was locked. We happened to see it just 1726 // after it was unlocked (and added to the free list). 1727 // Refetch the possibly changed next field and try again. 1728 cur_om = unmarked_next(in_use_tail); 1729 continue; 1730 } 1731 in_use_tail = cur_om; 1732 in_use_count++; 1733 cur_om = unmarked_next(cur_om); 1734 } 1735 guarantee(in_use_tail != NULL, "invariant"); 1736 int l_om_in_use_count = Atomic::load(&self->om_in_use_count); 1737 ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: " 1738 "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count); 1739 Atomic::store(&self->om_in_use_count, 0); 1740 // Clear the in-use list head (which also unlocks it): 1741 Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL); 1742 om_unlock(in_use_list); 1743 } 1744 1745 int free_count = 0; 1746 ObjectMonitor* free_list = NULL; 1747 ObjectMonitor* free_tail = NULL; 1748 // This function can race with a list walker thread so we lock the 1749 // list head to prevent confusion. 1750 if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) { 1751 // At this point, we have locked the free list head so a racing 1752 // thread cannot come in after us. However, a racing thread could 1753 // be ahead of us; we'll detect that and delay to let it finish. 1754 // 1755 // The thread is going away. Set 'free_tail' to the last per-thread free 1756 // monitor which will be linked to om_list_globals._free_list below. 1757 // 1758 // Account for the free list head before the loop since it is 1759 // already locked (by this thread): 1760 free_tail = free_list; 1761 free_count++; 1762 for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) { 1763 if (is_locked(s)) { 1764 // s is locked so there must be a racing walker thread ahead 1765 // of us so we'll give it a chance to finish. 1766 while (is_locked(s)) { 1767 os::naked_short_sleep(1); 1768 } 1769 } 1770 free_tail = s; 1771 free_count++; 1772 guarantee(s->object() == NULL, "invariant"); 1773 stringStream ss; 1774 guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss)); 1775 } 1776 guarantee(free_tail != NULL, "invariant"); 1777 int l_om_free_count = Atomic::load(&self->om_free_count); 1778 ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: " 1779 "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count); 1780 Atomic::store(&self->om_free_count, 0); 1781 Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL); 1782 om_unlock(free_list); 1783 } 1784 1785 if (free_tail != NULL) { 1786 prepend_list_to_global_free_list(free_list, free_tail, free_count); 1787 } 1788 1789 if (in_use_tail != NULL) { 1790 prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count); 1791 } 1792 1793 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1794 LogStreamHandle(Info, monitorinflation) lsh_info; 1795 LogStream* ls = NULL; 1796 if (log_is_enabled(Debug, monitorinflation)) { 1797 ls = &lsh_debug; 1798 } else if ((free_count != 0 || in_use_count != 0) && 1799 log_is_enabled(Info, monitorinflation)) { 1800 ls = &lsh_info; 1801 } 1802 if (ls != NULL) { 1803 ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d" 1804 ", in_use_count=%d" ", om_free_provision=%d", 1805 p2i(self), free_count, in_use_count, self->om_free_provision); 1806 } 1807 } 1808 1809 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1810 const oop obj, 1811 ObjectSynchronizer::InflateCause cause) { 1812 assert(event != NULL, "invariant"); 1813 assert(event->should_commit(), "invariant"); 1814 event->set_monitorClass(obj->klass()); 1815 event->set_address((uintptr_t)(void*)obj); 1816 event->set_cause((u1)cause); 1817 event->commit(); 1818 } 1819 1820 // Fast path code shared by multiple functions 1821 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle* omh_p, oop obj) { 1822 while (true) { 1823 markWord mark = obj->mark(); 1824 if (mark.has_monitor()) { 1825 if (!omh_p->save_om_ptr(obj, mark)) { 1826 // Lost a race with async deflation so try again. 1827 assert(AsyncDeflateIdleMonitors, "sanity check"); 1828 continue; 1829 } 1830 ObjectMonitor* monitor = omh_p->om_ptr(); 1831 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid"); 1832 markWord dmw = monitor->header(); 1833 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value()); 1834 return; 1835 } 1836 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal); 1837 return; 1838 } 1839 } 1840 1841 void ObjectSynchronizer::inflate(ObjectMonitorHandle* omh_p, Thread* self, 1842 oop object, const InflateCause cause) { 1843 // Inflate mutates the heap ... 1844 // Relaxing assertion for bug 6320749. 1845 assert(Universe::verify_in_progress() || 1846 !SafepointSynchronize::is_at_safepoint(), "invariant"); 1847 1848 EventJavaMonitorInflate event; 1849 1850 for (;;) { 1851 const markWord mark = object->mark(); 1852 assert(!mark.has_bias_pattern(), "invariant"); 1853 1854 // The mark can be in one of the following states: 1855 // * Inflated - just return 1856 // * Stack-locked - coerce it to inflated 1857 // * INFLATING - busy wait for conversion to complete 1858 // * Neutral - aggressively inflate the object. 1859 // * BIASED - Illegal. We should never see this 1860 1861 // CASE: inflated 1862 if (mark.has_monitor()) { 1863 if (!omh_p->save_om_ptr(object, mark)) { 1864 // Lost a race with async deflation so try again. 1865 assert(AsyncDeflateIdleMonitors, "sanity check"); 1866 continue; 1867 } 1868 ObjectMonitor* inf = omh_p->om_ptr(); 1869 markWord dmw = inf->header(); 1870 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1871 assert(inf->object() == object, "invariant"); 1872 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); 1873 return; 1874 } 1875 1876 // CASE: inflation in progress - inflating over a stack-lock. 1877 // Some other thread is converting from stack-locked to inflated. 1878 // Only that thread can complete inflation -- other threads must wait. 1879 // The INFLATING value is transient. 1880 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1881 // We could always eliminate polling by parking the thread on some auxiliary list. 1882 if (mark == markWord::INFLATING()) { 1883 read_stable_mark(object); 1884 continue; 1885 } 1886 1887 // CASE: stack-locked 1888 // Could be stack-locked either by this thread or by some other thread. 1889 // 1890 // Note that we allocate the objectmonitor speculatively, _before_ attempting 1891 // to install INFLATING into the mark word. We originally installed INFLATING, 1892 // allocated the objectmonitor, and then finally STed the address of the 1893 // objectmonitor into the mark. This was correct, but artificially lengthened 1894 // the interval in which INFLATED appeared in the mark, thus increasing 1895 // the odds of inflation contention. 1896 // 1897 // We now use per-thread private objectmonitor free lists. 1898 // These list are reprovisioned from the global free list outside the 1899 // critical INFLATING...ST interval. A thread can transfer 1900 // multiple objectmonitors en-mass from the global free list to its local free list. 1901 // This reduces coherency traffic and lock contention on the global free list. 1902 // Using such local free lists, it doesn't matter if the om_alloc() call appears 1903 // before or after the CAS(INFLATING) operation. 1904 // See the comments in om_alloc(). 1905 1906 LogStreamHandle(Trace, monitorinflation) lsh; 1907 1908 if (mark.has_locker()) { 1909 ObjectMonitor* m = om_alloc(self); 1910 // Optimistically prepare the objectmonitor - anticipate successful CAS 1911 // We do this before the CAS in order to minimize the length of time 1912 // in which INFLATING appears in the mark. 1913 m->Recycle(); 1914 m->_Responsible = NULL; 1915 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class 1916 1917 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1918 if (cmp != mark) { 1919 // om_release() will reset the allocation state from New to Free. 1920 om_release(self, m, true); 1921 continue; // Interference -- just retry 1922 } 1923 1924 // We've successfully installed INFLATING (0) into the mark-word. 1925 // This is the only case where 0 will appear in a mark-word. 1926 // Only the singular thread that successfully swings the mark-word 1927 // to 0 can perform (or more precisely, complete) inflation. 1928 // 1929 // Why do we CAS a 0 into the mark-word instead of just CASing the 1930 // mark-word from the stack-locked value directly to the new inflated state? 1931 // Consider what happens when a thread unlocks a stack-locked object. 1932 // It attempts to use CAS to swing the displaced header value from the 1933 // on-stack BasicLock back into the object header. Recall also that the 1934 // header value (hash code, etc) can reside in (a) the object header, or 1935 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1936 // header in an ObjectMonitor. The inflate() routine must copy the header 1937 // value from the BasicLock on the owner's stack to the ObjectMonitor, all 1938 // the while preserving the hashCode stability invariants. If the owner 1939 // decides to release the lock while the value is 0, the unlock will fail 1940 // and control will eventually pass from slow_exit() to inflate. The owner 1941 // will then spin, waiting for the 0 value to disappear. Put another way, 1942 // the 0 causes the owner to stall if the owner happens to try to 1943 // drop the lock (restoring the header from the BasicLock to the object) 1944 // while inflation is in-progress. This protocol avoids races that might 1945 // would otherwise permit hashCode values to change or "flicker" for an object. 1946 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1947 // 0 serves as a "BUSY" inflate-in-progress indicator. 1948 1949 1950 // fetch the displaced mark from the owner's stack. 1951 // The owner can't die or unwind past the lock while our INFLATING 1952 // object is in the mark. Furthermore the owner can't complete 1953 // an unlock on the object, either. 1954 markWord dmw = mark.displaced_mark_helper(); 1955 // Catch if the object's header is not neutral (not locked and 1956 // not marked is what we care about here). 1957 ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1958 1959 // Setup monitor fields to proper values -- prepare the monitor 1960 m->set_header(dmw); 1961 1962 // Optimization: if the mark.locker stack address is associated 1963 // with this thread we could simply set m->_owner = self. 1964 // Note that a thread can inflate an object 1965 // that it has stack-locked -- as might happen in wait() -- directly 1966 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1967 if (AsyncDeflateIdleMonitors) { 1968 m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker()); 1969 } else { 1970 m->set_owner_from(NULL, mark.locker()); 1971 } 1972 m->set_object(object); 1973 // TODO-FIXME: assert BasicLock->dhw != 0. 1974 1975 omh_p->set_om_ptr(m); 1976 1977 // Must preserve store ordering. The monitor state must 1978 // be stable at the time of publishing the monitor address. 1979 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1980 object->release_set_mark(markWord::encode(m)); 1981 1982 // Once ObjectMonitor is configured and the object is associated 1983 // with the ObjectMonitor, it is safe to allow async deflation: 1984 assert(m->is_new(), "freshly allocated monitor must be new"); 1985 m->set_allocation_state(ObjectMonitor::Old); 1986 1987 // Hopefully the performance counters are allocated on distinct cache lines 1988 // to avoid false sharing on MP systems ... 1989 OM_PERFDATA_OP(Inflations, inc()); 1990 if (log_is_enabled(Trace, monitorinflation)) { 1991 ResourceMark rm(self); 1992 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1993 INTPTR_FORMAT ", type='%s'", p2i(object), 1994 object->mark().value(), object->klass()->external_name()); 1995 } 1996 if (event.should_commit()) { 1997 post_monitor_inflate_event(&event, object, cause); 1998 } 1999 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free"); 2000 return; 2001 } 2002 2003 // CASE: neutral 2004 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 2005 // If we know we're inflating for entry it's better to inflate by swinging a 2006 // pre-locked ObjectMonitor pointer into the object header. A successful 2007 // CAS inflates the object *and* confers ownership to the inflating thread. 2008 // In the current implementation we use a 2-step mechanism where we CAS() 2009 // to inflate and then CAS() again to try to swing _owner from NULL to self. 2010 // An inflateTry() method that we could call from enter() would be useful. 2011 2012 // Catch if the object's header is not neutral (not locked and 2013 // not marked is what we care about here). 2014 ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 2015 ObjectMonitor* m = om_alloc(self); 2016 // prepare m for installation - set monitor to initial state 2017 m->Recycle(); 2018 m->set_header(mark); 2019 if (AsyncDeflateIdleMonitors) { 2020 // DEFLATER_MARKER is the only non-NULL value we should see here. 2021 m->try_set_owner_from(DEFLATER_MARKER, NULL); 2022 } 2023 m->set_object(object); 2024 m->_Responsible = NULL; 2025 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class 2026 2027 omh_p->set_om_ptr(m); 2028 2029 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 2030 m->set_header(markWord::zero()); 2031 m->set_object(NULL); 2032 m->Recycle(); 2033 omh_p->set_om_ptr(NULL); 2034 // om_release() will reset the allocation state from New to Free. 2035 om_release(self, m, true); 2036 m = NULL; 2037 continue; 2038 // interference - the markword changed - just retry. 2039 // The state-transitions are one-way, so there's no chance of 2040 // live-lock -- "Inflated" is an absorbing state. 2041 } 2042 2043 // Once the ObjectMonitor is configured and object is associated 2044 // with the ObjectMonitor, it is safe to allow async deflation: 2045 assert(m->is_new(), "freshly allocated monitor must be new"); 2046 m->set_allocation_state(ObjectMonitor::Old); 2047 2048 // Hopefully the performance counters are allocated on distinct 2049 // cache lines to avoid false sharing on MP systems ... 2050 OM_PERFDATA_OP(Inflations, inc()); 2051 if (log_is_enabled(Trace, monitorinflation)) { 2052 ResourceMark rm(self); 2053 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 2054 INTPTR_FORMAT ", type='%s'", p2i(object), 2055 object->mark().value(), object->klass()->external_name()); 2056 } 2057 if (event.should_commit()) { 2058 post_monitor_inflate_event(&event, object, cause); 2059 } 2060 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free"); 2061 return; 2062 } 2063 } 2064 2065 2066 // We maintain a list of in-use monitors for each thread. 2067 // 2068 // For safepoint based deflation: 2069 // deflate_thread_local_monitors() scans a single thread's in-use list, while 2070 // deflate_idle_monitors() scans only a global list of in-use monitors which 2071 // is populated only as a thread dies (see om_flush()). 2072 // 2073 // These operations are called at all safepoints, immediately after mutators 2074 // are stopped, but before any objects have moved. Collectively they traverse 2075 // the population of in-use monitors, deflating where possible. The scavenged 2076 // monitors are returned to the global monitor free list. 2077 // 2078 // Beware that we scavenge at *every* stop-the-world point. Having a large 2079 // number of monitors in-use could negatively impact performance. We also want 2080 // to minimize the total # of monitors in circulation, as they incur a small 2081 // footprint penalty. 2082 // 2083 // Perversely, the heap size -- and thus the STW safepoint rate -- 2084 // typically drives the scavenge rate. Large heaps can mean infrequent GC, 2085 // which in turn can mean large(r) numbers of ObjectMonitors in circulation. 2086 // This is an unfortunate aspect of this design. 2087 // 2088 // For async deflation: 2089 // If a special deflation request is made, then the safepoint based 2090 // deflation mechanism is used. Otherwise, an async deflation request 2091 // is registered with the ServiceThread and it is notified. 2092 2093 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) { 2094 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 2095 2096 // The per-thread in-use lists are handled in 2097 // ParallelSPCleanupThreadClosure::do_thread(). 2098 2099 if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) { 2100 // Use the older mechanism for the global in-use list or if a 2101 // special deflation has been requested before the safepoint. 2102 ObjectSynchronizer::deflate_idle_monitors(counters); 2103 return; 2104 } 2105 2106 log_debug(monitorinflation)("requesting async deflation of idle monitors."); 2107 // Request deflation of idle monitors by the ServiceThread: 2108 set_is_async_deflation_requested(true); 2109 MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag); 2110 ml.notify_all(); 2111 2112 if (log_is_enabled(Debug, monitorinflation)) { 2113 // exit_globals()'s call to audit_and_print_stats() is done 2114 // at the Info level and not at a safepoint. 2115 // For safepoint based deflation, audit_and_print_stats() is called 2116 // in ObjectSynchronizer::finish_deflate_idle_monitors() at the 2117 // Debug level at a safepoint. 2118 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */); 2119 } 2120 } 2121 2122 // Deflate a single monitor if not in-use 2123 // Return true if deflated, false if in-use 2124 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, 2125 ObjectMonitor** free_head_p, 2126 ObjectMonitor** free_tail_p) { 2127 bool deflated; 2128 // Normal case ... The monitor is associated with obj. 2129 const markWord mark = obj->mark(); 2130 guarantee(mark == markWord::encode(mid), "should match: mark=" 2131 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(), 2132 markWord::encode(mid).value()); 2133 // Make sure that mark.monitor() and markWord::encode() agree: 2134 guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT 2135 ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid)); 2136 const markWord dmw = mid->header(); 2137 guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 2138 2139 if (mid->is_busy() || mid->ref_count() != 0) { 2140 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor* 2141 // is in use so no deflation. 2142 deflated = false; 2143 } else { 2144 // Deflate the monitor if it is no longer being used 2145 // It's idle - scavenge and return to the global free list 2146 // plain old deflation ... 2147 if (log_is_enabled(Trace, monitorinflation)) { 2148 ResourceMark rm; 2149 log_trace(monitorinflation)("deflate_monitor: " 2150 "object=" INTPTR_FORMAT ", mark=" 2151 INTPTR_FORMAT ", type='%s'", p2i(obj), 2152 mark.value(), obj->klass()->external_name()); 2153 } 2154 2155 // Restore the header back to obj 2156 obj->release_set_mark(dmw); 2157 if (AsyncDeflateIdleMonitors) { 2158 // clear() expects the owner field to be NULL. 2159 // DEFLATER_MARKER is the only non-NULL value we should see here. 2160 mid->try_set_owner_from(DEFLATER_MARKER, NULL); 2161 } 2162 mid->clear(); 2163 2164 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT, 2165 p2i(mid->object())); 2166 assert(mid->is_free(), "invariant"); 2167 2168 // Move the deflated ObjectMonitor to the working free list 2169 // defined by free_head_p and free_tail_p. 2170 if (*free_head_p == NULL) *free_head_p = mid; 2171 if (*free_tail_p != NULL) { 2172 // We append to the list so the caller can use mid->_next_om 2173 // to fix the linkages in its context. 2174 ObjectMonitor* prevtail = *free_tail_p; 2175 // Should have been cleaned up by the caller: 2176 // Note: Should not have to lock prevtail here since we're at a 2177 // safepoint and ObjectMonitors on the local free list should 2178 // not be accessed in parallel. 2179 #ifdef ASSERT 2180 ObjectMonitor* l_next_om = prevtail->next_om(); 2181 #endif 2182 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om)); 2183 prevtail->set_next_om(mid); 2184 } 2185 *free_tail_p = mid; 2186 // At this point, mid->_next_om still refers to its current 2187 // value and another ObjectMonitor's _next_om field still 2188 // refers to this ObjectMonitor. Those linkages have to be 2189 // cleaned up by the caller who has the complete context. 2190 deflated = true; 2191 } 2192 return deflated; 2193 } 2194 2195 // Deflate the specified ObjectMonitor if not in-use using a JavaThread. 2196 // Returns true if it was deflated and false otherwise. 2197 // 2198 // The async deflation protocol sets owner to DEFLATER_MARKER and 2199 // makes ref_count negative as signals to contending threads that 2200 // an async deflation is in progress. There are a number of checks 2201 // as part of the protocol to make sure that the calling thread has 2202 // not lost the race to a contending thread or to a thread that just 2203 // wants to use the ObjectMonitor*. 2204 // 2205 // The ObjectMonitor has been successfully async deflated when: 2206 // (owner == DEFLATER_MARKER && ref_count < 0) 2207 // Contending threads or ObjectMonitor* using threads that see those 2208 // values know to retry their operation. 2209 // 2210 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid, 2211 ObjectMonitor** free_head_p, 2212 ObjectMonitor** free_tail_p) { 2213 assert(AsyncDeflateIdleMonitors, "sanity check"); 2214 assert(Thread::current()->is_Java_thread(), "precondition"); 2215 // A newly allocated ObjectMonitor should not be seen here so we 2216 // avoid an endless inflate/deflate cycle. 2217 assert(mid->is_old(), "must be old: allocation_state=%d", 2218 (int) mid->allocation_state()); 2219 2220 if (mid->is_busy() || mid->ref_count() != 0) { 2221 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor* 2222 // is in use so no deflation. 2223 return false; 2224 } 2225 2226 if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) == NULL) { 2227 // ObjectMonitor is not owned by another thread. Our setting 2228 // owner to DEFLATER_MARKER forces any contending thread through 2229 // the slow path. This is just the first part of the async 2230 // deflation dance. 2231 2232 if (mid->_contentions != 0 || mid->_waiters != 0) { 2233 // Another thread has raced to enter the ObjectMonitor after 2234 // mid->is_busy() above or has already entered and waited on 2235 // it which makes it busy so no deflation. Restore owner to 2236 // NULL if it is still DEFLATER_MARKER. 2237 mid->try_set_owner_from(DEFLATER_MARKER, NULL); 2238 return false; 2239 } 2240 2241 if (Atomic::cmpxchg(&mid->_ref_count, (jint)0, -max_jint) == 0) { 2242 // Make ref_count negative to force any contending threads or 2243 // ObjectMonitor* using threads to retry. This is the second 2244 // part of the async deflation dance. 2245 2246 if (mid->owner_is_DEFLATER_MARKER()) { 2247 // If owner is still DEFLATER_MARKER, then we have successfully 2248 // signaled any contending threads to retry. If it is not, then we 2249 // have lost the race to an entering thread and the ObjectMonitor 2250 // is now busy. This is the third and final part of the async 2251 // deflation dance. 2252 // Note: This owner check solves the ABA problem with ref_count 2253 // where another thread acquired the ObjectMonitor, finished 2254 // using it and restored the ref_count to zero. 2255 2256 // Sanity checks for the races: 2257 guarantee(mid->_contentions == 0, "must be 0: contentions=%d", 2258 mid->_contentions); 2259 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters); 2260 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq=" 2261 INTPTR_FORMAT, p2i(mid->_cxq)); 2262 guarantee(mid->_EntryList == NULL, 2263 "must be no entering threads: EntryList=" INTPTR_FORMAT, 2264 p2i(mid->_EntryList)); 2265 2266 const oop obj = (oop) mid->object(); 2267 if (log_is_enabled(Trace, monitorinflation)) { 2268 ResourceMark rm; 2269 log_trace(monitorinflation)("deflate_monitor_using_JT: " 2270 "object=" INTPTR_FORMAT ", mark=" 2271 INTPTR_FORMAT ", type='%s'", 2272 p2i(obj), obj->mark().value(), 2273 obj->klass()->external_name()); 2274 } 2275 2276 // Install the old mark word if nobody else has already done it. 2277 mid->install_displaced_markword_in_object(obj); 2278 mid->clear_using_JT(); 2279 2280 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT, 2281 p2i(mid->object())); 2282 assert(mid->is_free(), "must be free: allocation_state=%d", 2283 (int) mid->allocation_state()); 2284 2285 // Move the deflated ObjectMonitor to the working free list 2286 // defined by free_head_p and free_tail_p. 2287 if (*free_head_p == NULL) { 2288 // First one on the list. 2289 *free_head_p = mid; 2290 } 2291 if (*free_tail_p != NULL) { 2292 // We append to the list so the caller can use mid->_next_om 2293 // to fix the linkages in its context. 2294 ObjectMonitor* prevtail = *free_tail_p; 2295 // Should have been cleaned up by the caller: 2296 om_lock(prevtail); 2297 #ifdef ASSERT 2298 ObjectMonitor* l_next_om = unmarked_next(prevtail); 2299 #endif 2300 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om)); 2301 prevtail->set_next_om(mid); // prevtail now points to mid (and is unlocked) 2302 } 2303 *free_tail_p = mid; 2304 2305 // At this point, mid->_next_om still refers to its current 2306 // value and another ObjectMonitor's _next_om field still 2307 // refers to this ObjectMonitor. Those linkages have to be 2308 // cleaned up by the caller who has the complete context. 2309 2310 // We leave owner == DEFLATER_MARKER and ref_count < 0 2311 // to force any racing threads to retry. 2312 return true; // Success, ObjectMonitor has been deflated. 2313 } 2314 2315 // The owner was changed from DEFLATER_MARKER so we lost the 2316 // race since the ObjectMonitor is now busy. 2317 2318 // Add back max_jint to restore the ref_count field to its 2319 // proper value (which may not be what we saw above): 2320 Atomic::add(&mid->_ref_count, max_jint); 2321 2322 #ifdef ASSERT 2323 jint l_ref_count = mid->ref_count(); 2324 #endif 2325 assert(l_ref_count >= 0, "must not be negative: l_ref_count=%d, ref_count=%d", 2326 l_ref_count, mid->ref_count()); 2327 return false; 2328 } 2329 2330 // The ref_count was no longer 0 so we lost the race since the 2331 // ObjectMonitor is now busy or the ObjectMonitor* is now is use. 2332 // Restore owner to NULL if it is still DEFLATER_MARKER: 2333 mid->try_set_owner_from(DEFLATER_MARKER, NULL); 2334 } 2335 2336 // The owner field is no longer NULL so we lost the race since the 2337 // ObjectMonitor is now busy. 2338 return false; 2339 } 2340 2341 // Walk a given monitor list, and deflate idle monitors. 2342 // The given list could be a per-thread list or a global list. 2343 // 2344 // In the case of parallel processing of thread local monitor lists, 2345 // work is done by Threads::parallel_threads_do() which ensures that 2346 // each Java thread is processed by exactly one worker thread, and 2347 // thus avoid conflicts that would arise when worker threads would 2348 // process the same monitor lists concurrently. 2349 // 2350 // See also ParallelSPCleanupTask and 2351 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and 2352 // Threads::parallel_java_threads_do() in thread.cpp. 2353 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p, 2354 int* count_p, 2355 ObjectMonitor** free_head_p, 2356 ObjectMonitor** free_tail_p) { 2357 ObjectMonitor* cur_mid_in_use = NULL; 2358 ObjectMonitor* mid = NULL; 2359 ObjectMonitor* next = NULL; 2360 int deflated_count = 0; 2361 2362 // This list walk executes at a safepoint and does not race with any 2363 // other list walkers. 2364 2365 for (mid = Atomic::load(list_p); mid != NULL; mid = next) { 2366 next = unmarked_next(mid); 2367 oop obj = (oop) mid->object(); 2368 if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) { 2369 // Deflation succeeded and already updated free_head_p and 2370 // free_tail_p as needed. Finish the move to the local free list 2371 // by unlinking mid from the global or per-thread in-use list. 2372 if (cur_mid_in_use == NULL) { 2373 // mid is the list head so switch the list head to next: 2374 Atomic::store(list_p, next); 2375 } else { 2376 // Switch cur_mid_in_use's next field to next: 2377 cur_mid_in_use->set_next_om(next); 2378 } 2379 // At this point mid is disconnected from the in-use list. 2380 deflated_count++; 2381 Atomic::dec(count_p); 2382 // mid is current tail in the free_head_p list so NULL terminate it: 2383 mid->set_next_om(NULL); 2384 } else { 2385 cur_mid_in_use = mid; 2386 } 2387 } 2388 return deflated_count; 2389 } 2390 2391 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using 2392 // a JavaThread. Returns the number of deflated ObjectMonitors. The given 2393 // list could be a per-thread in-use list or the global in-use list. 2394 // If a safepoint has started, then we save state via saved_mid_in_use_p 2395 // and return to the caller to honor the safepoint. 2396 // 2397 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p, 2398 int* count_p, 2399 ObjectMonitor** free_head_p, 2400 ObjectMonitor** free_tail_p, 2401 ObjectMonitor** saved_mid_in_use_p) { 2402 assert(AsyncDeflateIdleMonitors, "sanity check"); 2403 JavaThread* self = JavaThread::current(); 2404 2405 ObjectMonitor* cur_mid_in_use = NULL; 2406 ObjectMonitor* mid = NULL; 2407 ObjectMonitor* next = NULL; 2408 ObjectMonitor* next_next = NULL; 2409 int deflated_count = 0; 2410 NoSafepointVerifier nsv; 2411 2412 // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go 2413 // protocol because om_release() can do list deletions in parallel; 2414 // this also prevents races with a list walker thread. We also 2415 // lock-next-next-as-we-go to prevent an om_flush() that is behind 2416 // this thread from passing us. 2417 if (*saved_mid_in_use_p == NULL) { 2418 // No saved state so start at the beginning. 2419 // Lock the list head so we can possibly deflate it: 2420 if ((mid = get_list_head_locked(list_p)) == NULL) { 2421 return 0; // The list is empty so nothing to deflate. 2422 } 2423 next = unmarked_next(mid); 2424 } else { 2425 // We're restarting after a safepoint so restore the necessary state 2426 // before we resume. 2427 cur_mid_in_use = *saved_mid_in_use_p; 2428 // Lock cur_mid_in_use so we can possibly update its 2429 // next field to extract a deflated ObjectMonitor. 2430 om_lock(cur_mid_in_use); 2431 mid = unmarked_next(cur_mid_in_use); 2432 if (mid == NULL) { 2433 om_unlock(cur_mid_in_use); 2434 *saved_mid_in_use_p = NULL; 2435 return 0; // The remainder is empty so nothing more to deflate. 2436 } 2437 // Lock mid so we can possibly deflate it: 2438 om_lock(mid); 2439 next = unmarked_next(mid); 2440 } 2441 2442 while (true) { 2443 // The current mid is locked at this point. If we have a 2444 // cur_mid_in_use, then it is also locked at this point. 2445 2446 if (next != NULL) { 2447 // We lock next so that an om_flush() thread that is behind us 2448 // cannot pass us when we unlock the current mid. 2449 om_lock(next); 2450 next_next = unmarked_next(next); 2451 } 2452 2453 // Only try to deflate if there is an associated Java object and if 2454 // mid is old (is not newly allocated and is not newly freed). 2455 if (mid->object() != NULL && mid->is_old() && 2456 deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) { 2457 // Deflation succeeded and already updated free_head_p and 2458 // free_tail_p as needed. Finish the move to the local free list 2459 // by unlinking mid from the global or per-thread in-use list. 2460 if (cur_mid_in_use == NULL) { 2461 // mid is the list head and it is locked. Switch the list head 2462 // to next which is also locked (if not NULL) and also leave 2463 // mid locked: 2464 Atomic::store(list_p, next); 2465 } else { 2466 ObjectMonitor* locked_next = mark_om_ptr(next); 2467 // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's 2468 // next field to locked_next and also leave mid locked: 2469 cur_mid_in_use->set_next_om(locked_next); 2470 } 2471 // At this point mid is disconnected from the in-use list so 2472 // its lock longer has any effects on in-use list. 2473 deflated_count++; 2474 Atomic::dec(count_p); 2475 // mid is current tail in the free_head_p list so NULL terminate it 2476 // (which also unlocks it): 2477 mid->set_next_om(NULL); 2478 2479 // All the list management is done so move on to the next one: 2480 mid = next; // mid keeps non-NULL next's locked state 2481 next = next_next; 2482 } else { 2483 // mid is considered in-use if it does not have an associated 2484 // Java object or mid is not old or deflation did not succeed. 2485 // A mid->is_new() node can be seen here when it is freshly 2486 // returned by om_alloc() (and skips the deflation code path). 2487 // A mid->is_old() node can be seen here when deflation failed. 2488 // A mid->is_free() node can be seen here when a fresh node from 2489 // om_alloc() is released by om_release() due to losing the race 2490 // in inflate(). 2491 2492 // All the list management is done so move on to the next one: 2493 if (cur_mid_in_use != NULL) { 2494 om_unlock(cur_mid_in_use); 2495 } 2496 // The next cur_mid_in_use keeps mid's lock state so 2497 // that it is stable for a possible next field change. It 2498 // cannot be modified by om_release() while it is locked. 2499 cur_mid_in_use = mid; 2500 mid = next; // mid keeps non-NULL next's locked state 2501 next = next_next; 2502 2503 if (SafepointMechanism::should_block(self) && 2504 cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) { 2505 // If a safepoint has started and cur_mid_in_use is not the list 2506 // head and is old, then it is safe to use as saved state. Return 2507 // to the caller before blocking. 2508 *saved_mid_in_use_p = cur_mid_in_use; 2509 om_unlock(cur_mid_in_use); 2510 if (mid != NULL) { 2511 om_unlock(mid); 2512 } 2513 return deflated_count; 2514 } 2515 } 2516 if (mid == NULL) { 2517 if (cur_mid_in_use != NULL) { 2518 om_unlock(cur_mid_in_use); 2519 } 2520 break; // Reached end of the list so nothing more to deflate. 2521 } 2522 2523 // The current mid's next field is locked at this point. If we have 2524 // a cur_mid_in_use, then it is also locked at this point. 2525 } 2526 // We finished the list without a safepoint starting so there's 2527 // no need to save state. 2528 *saved_mid_in_use_p = NULL; 2529 return deflated_count; 2530 } 2531 2532 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) { 2533 counters->n_in_use = 0; // currently associated with objects 2534 counters->n_in_circulation = 0; // extant 2535 counters->n_scavenged = 0; // reclaimed (global and per-thread) 2536 counters->per_thread_scavenged = 0; // per-thread scavenge total 2537 counters->per_thread_times = 0.0; // per-thread scavenge times 2538 } 2539 2540 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) { 2541 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 2542 2543 if (AsyncDeflateIdleMonitors) { 2544 // Nothing to do when global idle ObjectMonitors are deflated using 2545 // a JavaThread unless a special deflation has been requested. 2546 if (!is_special_deflation_requested()) { 2547 return; 2548 } 2549 } 2550 2551 bool deflated = false; 2552 2553 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors 2554 ObjectMonitor* free_tail_p = NULL; 2555 elapsedTimer timer; 2556 2557 if (log_is_enabled(Info, monitorinflation)) { 2558 timer.start(); 2559 } 2560 2561 // Note: the thread-local monitors lists get deflated in 2562 // a separate pass. See deflate_thread_local_monitors(). 2563 2564 // For moribund threads, scan om_list_globals._in_use_list 2565 int deflated_count = 0; 2566 if (Atomic::load(&om_list_globals._in_use_list) != NULL) { 2567 // Update n_in_circulation before om_list_globals._in_use_count is 2568 // updated by deflation. 2569 Atomic::add(&counters->n_in_circulation, 2570 Atomic::load(&om_list_globals._in_use_count)); 2571 2572 deflated_count = deflate_monitor_list(&om_list_globals._in_use_list, 2573 &om_list_globals._in_use_count, 2574 &free_head_p, &free_tail_p); 2575 Atomic::add(&counters->n_in_use, Atomic::load(&om_list_globals._in_use_count)); 2576 } 2577 2578 if (free_head_p != NULL) { 2579 // Move the deflated ObjectMonitors back to the global free list. 2580 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant"); 2581 #ifdef ASSERT 2582 ObjectMonitor* l_next_om = free_tail_p->next_om(); 2583 #endif 2584 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om)); 2585 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count); 2586 Atomic::add(&counters->n_scavenged, deflated_count); 2587 } 2588 timer.stop(); 2589 2590 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2591 LogStreamHandle(Info, monitorinflation) lsh_info; 2592 LogStream* ls = NULL; 2593 if (log_is_enabled(Debug, monitorinflation)) { 2594 ls = &lsh_debug; 2595 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 2596 ls = &lsh_info; 2597 } 2598 if (ls != NULL) { 2599 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count); 2600 } 2601 } 2602 2603 class HandshakeForDeflation : public HandshakeClosure { 2604 public: 2605 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {} 2606 2607 void do_thread(Thread* thread) { 2608 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread=" 2609 INTPTR_FORMAT, p2i(thread)); 2610 } 2611 }; 2612 2613 void ObjectSynchronizer::deflate_idle_monitors_using_JT() { 2614 assert(AsyncDeflateIdleMonitors, "sanity check"); 2615 2616 // Deflate any global idle monitors. 2617 deflate_global_idle_monitors_using_JT(); 2618 2619 int count = 0; 2620 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 2621 if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) { 2622 // This JavaThread is using ObjectMonitors so deflate any that 2623 // are idle unless this JavaThread is exiting; do not race with 2624 // ObjectSynchronizer::om_flush(). 2625 deflate_per_thread_idle_monitors_using_JT(jt); 2626 count++; 2627 } 2628 } 2629 if (count > 0) { 2630 log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count); 2631 } 2632 2633 log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, " 2634 "global_free_count=%d, global_wait_count=%d", 2635 Atomic::load(&om_list_globals._population), 2636 Atomic::load(&om_list_globals._in_use_count), 2637 Atomic::load(&om_list_globals._free_count), 2638 Atomic::load(&om_list_globals._wait_count)); 2639 2640 // The ServiceThread's async deflation request has been processed. 2641 set_is_async_deflation_requested(false); 2642 2643 if (Atomic::load(&om_list_globals._wait_count) > 0) { 2644 // There are deflated ObjectMonitors waiting for a handshake 2645 // (or a safepoint) for safety. 2646 2647 ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list); 2648 ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL"); 2649 int count = Atomic::load(&om_list_globals._wait_count); 2650 Atomic::store(&om_list_globals._wait_count, 0); 2651 Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL); 2652 2653 // Find the tail for prepend_list_to_common(). No need to mark 2654 // ObjectMonitors for this list walk since only the deflater 2655 // thread manages the wait list. 2656 int l_count = 0; 2657 ObjectMonitor* tail = NULL; 2658 for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) { 2659 tail = n; 2660 l_count++; 2661 } 2662 ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count); 2663 2664 // Will execute a safepoint if !ThreadLocalHandshakes: 2665 HandshakeForDeflation hfd_hc; 2666 Handshake::execute(&hfd_hc); 2667 2668 prepend_list_to_common(list, tail, count, &om_list_globals._free_list, 2669 &om_list_globals._free_count); 2670 2671 log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count); 2672 } 2673 } 2674 2675 // Deflate global idle ObjectMonitors using a JavaThread. 2676 // 2677 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() { 2678 assert(AsyncDeflateIdleMonitors, "sanity check"); 2679 assert(Thread::current()->is_Java_thread(), "precondition"); 2680 JavaThread* self = JavaThread::current(); 2681 2682 deflate_common_idle_monitors_using_JT(true /* is_global */, self); 2683 } 2684 2685 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread. 2686 // 2687 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) { 2688 assert(AsyncDeflateIdleMonitors, "sanity check"); 2689 assert(Thread::current()->is_Java_thread(), "precondition"); 2690 2691 deflate_common_idle_monitors_using_JT(false /* !is_global */, target); 2692 } 2693 2694 // Deflate global or per-thread idle ObjectMonitors using a JavaThread. 2695 // 2696 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) { 2697 JavaThread* self = JavaThread::current(); 2698 2699 int deflated_count = 0; 2700 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged ObjectMonitors 2701 ObjectMonitor* free_tail_p = NULL; 2702 ObjectMonitor* saved_mid_in_use_p = NULL; 2703 elapsedTimer timer; 2704 2705 if (log_is_enabled(Info, monitorinflation)) { 2706 timer.start(); 2707 } 2708 2709 if (is_global) { 2710 OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count))); 2711 } else { 2712 OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count))); 2713 } 2714 2715 do { 2716 int local_deflated_count; 2717 if (is_global) { 2718 local_deflated_count = 2719 deflate_monitor_list_using_JT(&om_list_globals._in_use_list, 2720 &om_list_globals._in_use_count, 2721 &free_head_p, &free_tail_p, 2722 &saved_mid_in_use_p); 2723 } else { 2724 local_deflated_count = 2725 deflate_monitor_list_using_JT(&target->om_in_use_list, 2726 &target->om_in_use_count, &free_head_p, 2727 &free_tail_p, &saved_mid_in_use_p); 2728 } 2729 deflated_count += local_deflated_count; 2730 2731 if (free_head_p != NULL) { 2732 // Move the deflated ObjectMonitors to the global free list. 2733 guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count); 2734 // Note: The target thread can be doing an om_alloc() that 2735 // is trying to prepend an ObjectMonitor on its in-use list 2736 // at the same time that we have deflated the current in-use 2737 // list head and put it on the local free list. prepend_to_common() 2738 // will detect the race and retry which avoids list corruption, 2739 // but the next field in free_tail_p can flicker to marked 2740 // and then unmarked while prepend_to_common() is sorting it 2741 // all out. 2742 #ifdef ASSERT 2743 ObjectMonitor* l_next_om = unmarked_next(free_tail_p); 2744 #endif 2745 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om)); 2746 2747 prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count); 2748 2749 OM_PERFDATA_OP(Deflations, inc(local_deflated_count)); 2750 } 2751 2752 if (saved_mid_in_use_p != NULL) { 2753 // deflate_monitor_list_using_JT() detected a safepoint starting. 2754 timer.stop(); 2755 { 2756 if (is_global) { 2757 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint."); 2758 } else { 2759 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target)); 2760 } 2761 assert(SafepointMechanism::should_block(self), "sanity check"); 2762 ThreadBlockInVM blocker(self); 2763 } 2764 // Prepare for another loop after the safepoint. 2765 free_head_p = NULL; 2766 free_tail_p = NULL; 2767 if (log_is_enabled(Info, monitorinflation)) { 2768 timer.start(); 2769 } 2770 } 2771 } while (saved_mid_in_use_p != NULL); 2772 timer.stop(); 2773 2774 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2775 LogStreamHandle(Info, monitorinflation) lsh_info; 2776 LogStream* ls = NULL; 2777 if (log_is_enabled(Debug, monitorinflation)) { 2778 ls = &lsh_debug; 2779 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 2780 ls = &lsh_info; 2781 } 2782 if (ls != NULL) { 2783 if (is_global) { 2784 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count); 2785 } else { 2786 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count); 2787 } 2788 } 2789 } 2790 2791 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) { 2792 // Report the cumulative time for deflating each thread's idle 2793 // monitors. Note: if the work is split among more than one 2794 // worker thread, then the reported time will likely be more 2795 // than a beginning to end measurement of the phase. 2796 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged); 2797 2798 bool needs_special_deflation = is_special_deflation_requested(); 2799 if (AsyncDeflateIdleMonitors && !needs_special_deflation) { 2800 // Nothing to do when idle ObjectMonitors are deflated using 2801 // a JavaThread unless a special deflation has been requested. 2802 return; 2803 } 2804 2805 if (log_is_enabled(Debug, monitorinflation)) { 2806 // exit_globals()'s call to audit_and_print_stats() is done 2807 // at the Info level and not at a safepoint. 2808 // For async deflation, audit_and_print_stats() is called in 2809 // ObjectSynchronizer::do_safepoint_work() at the Debug level 2810 // at a safepoint. 2811 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */); 2812 } else if (log_is_enabled(Info, monitorinflation)) { 2813 log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, " 2814 "global_free_count=%d, global_wait_count=%d", 2815 Atomic::load(&om_list_globals._population), 2816 Atomic::load(&om_list_globals._in_use_count), 2817 Atomic::load(&om_list_globals._free_count), 2818 Atomic::load(&om_list_globals._wait_count)); 2819 } 2820 2821 Atomic::store(&_forceMonitorScavenge, 0); // Reset 2822 2823 OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged)); 2824 OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation)); 2825 2826 GVars.stw_random = os::random(); 2827 GVars.stw_cycle++; 2828 2829 if (needs_special_deflation) { 2830 set_is_special_deflation_requested(false); // special deflation is done 2831 } 2832 } 2833 2834 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) { 2835 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); 2836 2837 if (AsyncDeflateIdleMonitors && !is_special_deflation_requested()) { 2838 // Nothing to do if a special deflation has NOT been requested. 2839 return; 2840 } 2841 2842 ObjectMonitor* free_head_p = NULL; // Local SLL of scavenged monitors 2843 ObjectMonitor* free_tail_p = NULL; 2844 elapsedTimer timer; 2845 2846 if (log_is_enabled(Info, safepoint, cleanup) || 2847 log_is_enabled(Info, monitorinflation)) { 2848 timer.start(); 2849 } 2850 2851 // Update n_in_circulation before om_in_use_count is updated by deflation. 2852 Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count)); 2853 2854 int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p); 2855 Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count)); 2856 2857 if (free_head_p != NULL) { 2858 // Move the deflated ObjectMonitors back to the global free list. 2859 guarantee(free_tail_p != NULL && deflated_count > 0, "invariant"); 2860 #ifdef ASSERT 2861 ObjectMonitor* l_next_om = free_tail_p->next_om(); 2862 #endif 2863 assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om)); 2864 prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count); 2865 Atomic::add(&counters->n_scavenged, deflated_count); 2866 Atomic::add(&counters->per_thread_scavenged, deflated_count); 2867 } 2868 2869 timer.stop(); 2870 counters->per_thread_times += timer.seconds(); 2871 2872 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2873 LogStreamHandle(Info, monitorinflation) lsh_info; 2874 LogStream* ls = NULL; 2875 if (log_is_enabled(Debug, monitorinflation)) { 2876 ls = &lsh_debug; 2877 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) { 2878 ls = &lsh_info; 2879 } 2880 if (ls != NULL) { 2881 ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count); 2882 } 2883 } 2884 2885 // Monitor cleanup on JavaThread::exit 2886 2887 // Iterate through monitor cache and attempt to release thread's monitors 2888 // Gives up on a particular monitor if an exception occurs, but continues 2889 // the overall iteration, swallowing the exception. 2890 class ReleaseJavaMonitorsClosure: public MonitorClosure { 2891 private: 2892 TRAPS; 2893 2894 public: 2895 ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} 2896 void do_monitor(ObjectMonitor* mid) { 2897 if (mid->owner() == THREAD) { 2898 (void)mid->complete_exit(CHECK); 2899 } 2900 } 2901 }; 2902 2903 // Release all inflated monitors owned by THREAD. Lightweight monitors are 2904 // ignored. This is meant to be called during JNI thread detach which assumes 2905 // all remaining monitors are heavyweight. All exceptions are swallowed. 2906 // Scanning the extant monitor list can be time consuming. 2907 // A simple optimization is to add a per-thread flag that indicates a thread 2908 // called jni_monitorenter() during its lifetime. 2909 // 2910 // Instead of No_Savepoint_Verifier it might be cheaper to 2911 // use an idiom of the form: 2912 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 2913 // <code that must not run at safepoint> 2914 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 2915 // Since the tests are extremely cheap we could leave them enabled 2916 // for normal product builds. 2917 2918 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { 2919 assert(THREAD == JavaThread::current(), "must be current Java thread"); 2920 NoSafepointVerifier nsv; 2921 ReleaseJavaMonitorsClosure rjmc(THREAD); 2922 ObjectSynchronizer::monitors_iterate(&rjmc); 2923 THREAD->clear_pending_exception(); 2924 } 2925 2926 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 2927 switch (cause) { 2928 case inflate_cause_vm_internal: return "VM Internal"; 2929 case inflate_cause_monitor_enter: return "Monitor Enter"; 2930 case inflate_cause_wait: return "Monitor Wait"; 2931 case inflate_cause_notify: return "Monitor Notify"; 2932 case inflate_cause_hash_code: return "Monitor Hash Code"; 2933 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 2934 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 2935 default: 2936 ShouldNotReachHere(); 2937 } 2938 return "Unknown"; 2939 } 2940 2941 //------------------------------------------------------------------------------ 2942 // Debugging code 2943 2944 u_char* ObjectSynchronizer::get_gvars_addr() { 2945 return (u_char*)&GVars; 2946 } 2947 2948 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() { 2949 return (u_char*)&GVars.hc_sequence; 2950 } 2951 2952 size_t ObjectSynchronizer::get_gvars_size() { 2953 return sizeof(SharedGlobals); 2954 } 2955 2956 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() { 2957 return (u_char*)&GVars.stw_random; 2958 } 2959 2960 // This function can be called at a safepoint or it can be called when 2961 // we are trying to exit the VM. When we are trying to exit the VM, the 2962 // list walker functions can run in parallel with the other list 2963 // operations so spin-locking is used for safety. 2964 // 2965 // Calls to this function can be added in various places as a debugging 2966 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor 2967 // details logged at the Info level and 'false' for the 'on_exit' 2968 // parameter to have in-use monitor details logged at the Trace level. 2969 // deflate_monitor_list() no longer uses spin-locking so be careful 2970 // when adding audit_and_print_stats() calls at a safepoint. 2971 // 2972 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 2973 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 2974 2975 LogStreamHandle(Debug, monitorinflation) lsh_debug; 2976 LogStreamHandle(Info, monitorinflation) lsh_info; 2977 LogStreamHandle(Trace, monitorinflation) lsh_trace; 2978 LogStream* ls = NULL; 2979 if (log_is_enabled(Trace, monitorinflation)) { 2980 ls = &lsh_trace; 2981 } else if (log_is_enabled(Debug, monitorinflation)) { 2982 ls = &lsh_debug; 2983 } else if (log_is_enabled(Info, monitorinflation)) { 2984 ls = &lsh_info; 2985 } 2986 assert(ls != NULL, "sanity check"); 2987 2988 // Log counts for the global and per-thread monitor lists: 2989 int chk_om_population = log_monitor_list_counts(ls); 2990 int error_cnt = 0; 2991 2992 ls->print_cr("Checking global lists:"); 2993 2994 // Check om_list_globals._population: 2995 if (Atomic::load(&om_list_globals._population) == chk_om_population) { 2996 ls->print_cr("global_population=%d equals chk_om_population=%d", 2997 Atomic::load(&om_list_globals._population), chk_om_population); 2998 } else { 2999 // With fine grained locks on the monitor lists, it is possible for 3000 // log_monitor_list_counts() to return a value that doesn't match 3001 // om_list_globals._population. So far a higher value has been 3002 // seen in testing so something is being double counted by 3003 // log_monitor_list_counts(). 3004 ls->print_cr("WARNING: global_population=%d is not equal to " 3005 "chk_om_population=%d", 3006 Atomic::load(&om_list_globals._population), chk_om_population); 3007 } 3008 3009 // Check om_list_globals._in_use_list and om_list_globals._in_use_count: 3010 chk_global_in_use_list_and_count(ls, &error_cnt); 3011 3012 // Check om_list_globals._free_list and om_list_globals._free_count: 3013 chk_global_free_list_and_count(ls, &error_cnt); 3014 3015 // Check om_list_globals._wait_list and om_list_globals._wait_count: 3016 chk_global_wait_list_and_count(ls, &error_cnt); 3017 3018 ls->print_cr("Checking per-thread lists:"); 3019 3020 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 3021 // Check om_in_use_list and om_in_use_count: 3022 chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt); 3023 3024 // Check om_free_list and om_free_count: 3025 chk_per_thread_free_list_and_count(jt, ls, &error_cnt); 3026 } 3027 3028 if (error_cnt == 0) { 3029 ls->print_cr("No errors found in monitor list checks."); 3030 } else { 3031 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt); 3032 } 3033 3034 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 3035 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 3036 // When exiting this log output is at the Info level. When called 3037 // at a safepoint, this log output is at the Trace level since 3038 // there can be a lot of it. 3039 log_in_use_monitor_details(ls); 3040 } 3041 3042 ls->flush(); 3043 3044 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 3045 } 3046 3047 // Check a free monitor entry; log any errors. 3048 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n, 3049 outputStream * out, int *error_cnt_p) { 3050 stringStream ss; 3051 if (n->is_busy()) { 3052 if (jt != NULL) { 3053 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3054 ": free per-thread monitor must not be busy: %s", p2i(jt), 3055 p2i(n), n->is_busy_to_string(&ss)); 3056 } else { 3057 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 3058 "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss)); 3059 } 3060 *error_cnt_p = *error_cnt_p + 1; 3061 } 3062 if (n->header().value() != 0) { 3063 if (jt != NULL) { 3064 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3065 ": free per-thread monitor must have NULL _header " 3066 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n), 3067 n->header().value()); 3068 *error_cnt_p = *error_cnt_p + 1; 3069 } else if (!AsyncDeflateIdleMonitors) { 3070 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 3071 "must have NULL _header field: _header=" INTPTR_FORMAT, 3072 p2i(n), n->header().value()); 3073 *error_cnt_p = *error_cnt_p + 1; 3074 } 3075 } 3076 if (n->object() != NULL) { 3077 if (jt != NULL) { 3078 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3079 ": free per-thread monitor must have NULL _object " 3080 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n), 3081 p2i(n->object())); 3082 } else { 3083 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor " 3084 "must have NULL _object field: _object=" INTPTR_FORMAT, 3085 p2i(n), p2i(n->object())); 3086 } 3087 *error_cnt_p = *error_cnt_p + 1; 3088 } 3089 } 3090 3091 // Lock the next ObjectMonitor for traversal and unlock the current 3092 // ObjectMonitor. Returns the next ObjectMonitor if there is one. 3093 // Otherwise returns NULL (after unlocking the current ObjectMonitor). 3094 // This function is used by the various list walker functions to 3095 // safely walk a list without allowing an ObjectMonitor to be moved 3096 // to another list in the middle of a walk. 3097 static ObjectMonitor* lock_next_for_traversal(ObjectMonitor* cur) { 3098 assert(is_locked(cur), "cur=" INTPTR_FORMAT " must be locked", p2i(cur)); 3099 ObjectMonitor* next = unmarked_next(cur); 3100 if (next == NULL) { // Reached the end of the list. 3101 om_unlock(cur); 3102 return NULL; 3103 } 3104 om_lock(next); // Lock next before unlocking current to keep 3105 om_unlock(cur); // from being by-passed by another thread. 3106 return next; 3107 } 3108 3109 // Check the global free list and count; log the results of the checks. 3110 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out, 3111 int *error_cnt_p) { 3112 int chk_om_free_count = 0; 3113 ObjectMonitor* cur = NULL; 3114 if ((cur = get_list_head_locked(&om_list_globals._free_list)) != NULL) { 3115 // Marked the global free list head so process the list. 3116 while (true) { 3117 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p); 3118 chk_om_free_count++; 3119 3120 cur = lock_next_for_traversal(cur); 3121 if (cur == NULL) { 3122 break; 3123 } 3124 } 3125 } 3126 int l_free_count = Atomic::load(&om_list_globals._free_count); 3127 if (l_free_count == chk_om_free_count) { 3128 out->print_cr("global_free_count=%d equals chk_om_free_count=%d", 3129 l_free_count, chk_om_free_count); 3130 } else { 3131 // With fine grained locks on om_list_globals._free_list, it 3132 // is possible for an ObjectMonitor to be prepended to 3133 // om_list_globals._free_list after we started calculating 3134 // chk_om_free_count so om_list_globals._free_count may not 3135 // match anymore. 3136 out->print_cr("WARNING: global_free_count=%d is not equal to " 3137 "chk_om_free_count=%d", l_free_count, chk_om_free_count); 3138 } 3139 } 3140 3141 // Check the global wait list and count; log the results of the checks. 3142 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out, 3143 int *error_cnt_p) { 3144 int chk_om_wait_count = 0; 3145 ObjectMonitor* cur = NULL; 3146 if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) { 3147 // Marked the global wait list head so process the list. 3148 while (true) { 3149 // Rules for om_list_globals._wait_list are the same as for 3150 // om_list_globals._free_list: 3151 chk_free_entry(NULL /* jt */, cur, out, error_cnt_p); 3152 chk_om_wait_count++; 3153 3154 cur = lock_next_for_traversal(cur); 3155 if (cur == NULL) { 3156 break; 3157 } 3158 } 3159 } 3160 if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) { 3161 out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d", 3162 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count); 3163 } else { 3164 out->print_cr("ERROR: global_wait_count=%d is not equal to " 3165 "chk_om_wait_count=%d", 3166 Atomic::load(&om_list_globals._wait_count), chk_om_wait_count); 3167 *error_cnt_p = *error_cnt_p + 1; 3168 } 3169 } 3170 3171 // Check the global in-use list and count; log the results of the checks. 3172 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out, 3173 int *error_cnt_p) { 3174 int chk_om_in_use_count = 0; 3175 ObjectMonitor* cur = NULL; 3176 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) { 3177 // Marked the global in-use list head so process the list. 3178 while (true) { 3179 chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p); 3180 chk_om_in_use_count++; 3181 3182 cur = lock_next_for_traversal(cur); 3183 if (cur == NULL) { 3184 break; 3185 } 3186 } 3187 } 3188 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count); 3189 if (l_in_use_count == chk_om_in_use_count) { 3190 out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d", 3191 l_in_use_count, chk_om_in_use_count); 3192 } else { 3193 // With fine grained locks on the monitor lists, it is possible for 3194 // an exiting JavaThread to put its in-use ObjectMonitors on the 3195 // global in-use list after chk_om_in_use_count is calculated above. 3196 out->print_cr("WARNING: global_in_use_count=%d is not equal to chk_om_in_use_count=%d", 3197 l_in_use_count, chk_om_in_use_count); 3198 } 3199 } 3200 3201 // Check an in-use monitor entry; log any errors. 3202 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n, 3203 outputStream * out, int *error_cnt_p) { 3204 if (n->header().value() == 0) { 3205 if (jt != NULL) { 3206 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3207 ": in-use per-thread monitor must have non-NULL _header " 3208 "field.", p2i(jt), p2i(n)); 3209 } else { 3210 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor " 3211 "must have non-NULL _header field.", p2i(n)); 3212 } 3213 *error_cnt_p = *error_cnt_p + 1; 3214 } 3215 if (n->object() == NULL) { 3216 if (jt != NULL) { 3217 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3218 ": in-use per-thread monitor must have non-NULL _object " 3219 "field.", p2i(jt), p2i(n)); 3220 } else { 3221 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor " 3222 "must have non-NULL _object field.", p2i(n)); 3223 } 3224 *error_cnt_p = *error_cnt_p + 1; 3225 } 3226 const oop obj = (oop)n->object(); 3227 const markWord mark = obj->mark(); 3228 if (!mark.has_monitor()) { 3229 if (jt != NULL) { 3230 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3231 ": in-use per-thread monitor's object does not think " 3232 "it has a monitor: obj=" INTPTR_FORMAT ", mark=" 3233 INTPTR_FORMAT, p2i(jt), p2i(n), p2i(obj), mark.value()); 3234 } else { 3235 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global " 3236 "monitor's object does not think it has a monitor: obj=" 3237 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 3238 p2i(obj), mark.value()); 3239 } 3240 *error_cnt_p = *error_cnt_p + 1; 3241 } 3242 ObjectMonitor* const obj_mon = mark.monitor(); 3243 if (n != obj_mon) { 3244 if (jt != NULL) { 3245 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT 3246 ": in-use per-thread monitor's object does not refer " 3247 "to the same monitor: obj=" INTPTR_FORMAT ", mark=" 3248 INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt), 3249 p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 3250 } else { 3251 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global " 3252 "monitor's object does not refer to the same monitor: obj=" 3253 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 3254 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 3255 } 3256 *error_cnt_p = *error_cnt_p + 1; 3257 } 3258 } 3259 3260 // Check the thread's free list and count; log the results of the checks. 3261 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt, 3262 outputStream * out, 3263 int *error_cnt_p) { 3264 int chk_om_free_count = 0; 3265 ObjectMonitor* cur = NULL; 3266 if ((cur = get_list_head_locked(&jt->om_free_list)) != NULL) { 3267 // Marked the per-thread free list head so process the list. 3268 while (true) { 3269 chk_free_entry(jt, cur, out, error_cnt_p); 3270 chk_om_free_count++; 3271 3272 cur = lock_next_for_traversal(cur); 3273 if (cur == NULL) { 3274 break; 3275 } 3276 } 3277 } 3278 int l_om_free_count = Atomic::load(&jt->om_free_count); 3279 if (l_om_free_count == chk_om_free_count) { 3280 out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals " 3281 "chk_om_free_count=%d", p2i(jt), l_om_free_count, chk_om_free_count); 3282 } else { 3283 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not " 3284 "equal to chk_om_free_count=%d", p2i(jt), l_om_free_count, 3285 chk_om_free_count); 3286 *error_cnt_p = *error_cnt_p + 1; 3287 } 3288 } 3289 3290 // Check the thread's in-use list and count; log the results of the checks. 3291 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt, 3292 outputStream * out, 3293 int *error_cnt_p) { 3294 int chk_om_in_use_count = 0; 3295 ObjectMonitor* cur = NULL; 3296 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) { 3297 // Marked the per-thread in-use list head so process the list. 3298 while (true) { 3299 chk_in_use_entry(jt, cur, out, error_cnt_p); 3300 chk_om_in_use_count++; 3301 3302 cur = lock_next_for_traversal(cur); 3303 if (cur == NULL) { 3304 break; 3305 } 3306 } 3307 } 3308 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count); 3309 if (l_om_in_use_count == chk_om_in_use_count) { 3310 out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals " 3311 "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count, 3312 chk_om_in_use_count); 3313 } else { 3314 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not " 3315 "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count, 3316 chk_om_in_use_count); 3317 *error_cnt_p = *error_cnt_p + 1; 3318 } 3319 } 3320 3321 // Log details about ObjectMonitors on the in-use lists. The 'BHL' 3322 // flags indicate why the entry is in-use, 'object' and 'object type' 3323 // indicate the associated object and its type. 3324 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) { 3325 stringStream ss; 3326 if (Atomic::load(&om_list_globals._in_use_count) > 0) { 3327 out->print_cr("In-use global monitor info:"); 3328 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 3329 out->print_cr("%18s %s %7s %18s %18s", 3330 "monitor", "BHL", "ref_cnt", "object", "object type"); 3331 out->print_cr("================== === ======= ================== =================="); 3332 ObjectMonitor* cur = NULL; 3333 if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) { 3334 // Marked the global in-use list head so process the list. 3335 while (true) { 3336 const oop obj = (oop) cur->object(); 3337 const markWord mark = cur->header(); 3338 ResourceMark rm; 3339 out->print(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s", p2i(cur), 3340 cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL, 3341 (int)cur->ref_count(), p2i(obj), obj->klass()->external_name()); 3342 if (cur->is_busy() != 0) { 3343 out->print(" (%s)", cur->is_busy_to_string(&ss)); 3344 ss.reset(); 3345 } 3346 out->cr(); 3347 3348 cur = lock_next_for_traversal(cur); 3349 if (cur == NULL) { 3350 break; 3351 } 3352 } 3353 } 3354 } 3355 3356 out->print_cr("In-use per-thread monitor info:"); 3357 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 3358 out->print_cr("%18s %18s %s %7s %18s %18s", 3359 "jt", "monitor", "BHL", "ref_cnt", "object", "object type"); 3360 out->print_cr("================== ================== === ======= ================== =================="); 3361 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 3362 ObjectMonitor* cur = NULL; 3363 if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) { 3364 // Marked the global in-use list head so process the list. 3365 while (true) { 3366 const oop obj = (oop) cur->object(); 3367 const markWord mark = cur->header(); 3368 ResourceMark rm; 3369 out->print(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT 3370 " %s", p2i(jt), p2i(cur), cur->is_busy() != 0, 3371 mark.hash() != 0, cur->owner() != NULL, (int)cur->ref_count(), 3372 p2i(obj), obj->klass()->external_name()); 3373 if (cur->is_busy() != 0) { 3374 out->print(" (%s)", cur->is_busy_to_string(&ss)); 3375 ss.reset(); 3376 } 3377 out->cr(); 3378 3379 cur = lock_next_for_traversal(cur); 3380 if (cur == NULL) { 3381 break; 3382 } 3383 } 3384 } 3385 } 3386 3387 out->flush(); 3388 } 3389 3390 // Log counts for the global and per-thread monitor lists and return 3391 // the population count. 3392 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) { 3393 int pop_count = 0; 3394 out->print_cr("%18s %10s %10s %10s %10s", 3395 "Global Lists:", "InUse", "Free", "Wait", "Total"); 3396 out->print_cr("================== ========== ========== ========== =========="); 3397 int l_in_use_count = Atomic::load(&om_list_globals._in_use_count); 3398 int l_free_count = Atomic::load(&om_list_globals._free_count); 3399 int l_wait_count = Atomic::load(&om_list_globals._wait_count); 3400 out->print_cr("%18s %10d %10d %10d %10d", "", l_in_use_count, 3401 l_free_count, l_wait_count, 3402 Atomic::load(&om_list_globals._population)); 3403 pop_count += l_in_use_count + l_free_count + l_wait_count; 3404 3405 out->print_cr("%18s %10s %10s %10s", 3406 "Per-Thread Lists:", "InUse", "Free", "Provision"); 3407 out->print_cr("================== ========== ========== =========="); 3408 3409 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) { 3410 int l_om_in_use_count = Atomic::load(&jt->om_in_use_count); 3411 int l_om_free_count = Atomic::load(&jt->om_free_count); 3412 out->print_cr(INTPTR_FORMAT " %10d %10d %10d", p2i(jt), 3413 l_om_in_use_count, l_om_free_count, jt->om_free_provision); 3414 pop_count += l_om_in_use_count + l_om_free_count; 3415 } 3416 return pop_count; 3417 } 3418 3419 #ifndef PRODUCT 3420 3421 // Check if monitor belongs to the monitor cache 3422 // The list is grow-only so it's *relatively* safe to traverse 3423 // the list of extant blocks without taking a lock. 3424 3425 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { 3426 PaddedObjectMonitor* block = Atomic::load(&g_block_list); 3427 while (block != NULL) { 3428 assert(block->object() == CHAINMARKER, "must be a block header"); 3429 if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { 3430 address mon = (address)monitor; 3431 address blk = (address)block; 3432 size_t diff = mon - blk; 3433 assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned"); 3434 return 1; 3435 } 3436 // unmarked_next() is not needed with g_block_list (no locking 3437 // used with block linkage _next_om fields). 3438 block = (PaddedObjectMonitor*)block->next_om(); 3439 } 3440 return 0; 3441 } 3442 3443 #endif