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