1 /* 2 * Copyright (c) 2005, 2019, 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/classLoaderDataGraph.hpp" 27 #include "jfr/jfrEvents.hpp" 28 #include "jfr/support/jfrThreadId.hpp" 29 #include "logging/log.hpp" 30 #include "memory/resourceArea.hpp" 31 #include "oops/klass.inline.hpp" 32 #include "oops/markWord.hpp" 33 #include "oops/oop.inline.hpp" 34 #include "runtime/atomic.hpp" 35 #include "runtime/basicLock.hpp" 36 #include "runtime/biasedLocking.hpp" 37 #include "runtime/handles.inline.hpp" 38 #include "runtime/handshake.hpp" 39 #include "runtime/task.hpp" 40 #include "runtime/threadSMR.hpp" 41 #include "runtime/vframe.hpp" 42 #include "runtime/vmThread.hpp" 43 #include "runtime/vmOperations.hpp" 44 45 46 static bool _biased_locking_enabled = false; 47 BiasedLockingCounters BiasedLocking::_counters; 48 49 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 50 static GrowableArray<markWord>* _preserved_mark_stack = NULL; 51 52 static void enable_biased_locking(InstanceKlass* k) { 53 k->set_prototype_header(markWord::biased_locking_prototype()); 54 } 55 56 static void enable_biased_locking() { 57 _biased_locking_enabled = true; 58 log_info(biasedlocking)("Biased locking enabled"); 59 } 60 61 class VM_EnableBiasedLocking: public VM_Operation { 62 public: 63 VM_EnableBiasedLocking() {} 64 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 65 66 void doit() { 67 // Iterate the class loader data dictionaries enabling biased locking for all 68 // currently loaded classes. 69 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking); 70 // Indicate that future instances should enable it as well 71 enable_biased_locking(); 72 } 73 74 bool allow_nested_vm_operations() const { return false; } 75 }; 76 77 78 // One-shot PeriodicTask subclass for enabling biased locking 79 class EnableBiasedLockingTask : public PeriodicTask { 80 public: 81 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 82 83 virtual void task() { 84 VM_EnableBiasedLocking op; 85 VMThread::execute(&op); 86 87 // Reclaim our storage and disenroll ourself 88 delete this; 89 } 90 }; 91 92 93 void BiasedLocking::init() { 94 // If biased locking is enabled and BiasedLockingStartupDelay is set, 95 // schedule a task to fire after the specified delay which turns on 96 // biased locking for all currently loaded classes as well as future 97 // ones. This could be a workaround for startup time regressions 98 // due to large number of safepoints being taken during VM startup for 99 // bias revocation. 100 if (UseBiasedLocking) { 101 if (BiasedLockingStartupDelay > 0) { 102 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 103 task->enroll(); 104 } else { 105 enable_biased_locking(); 106 } 107 } 108 } 109 110 111 bool BiasedLocking::enabled() { 112 assert(UseBiasedLocking, "precondition"); 113 // We check "BiasedLockingStartupDelay == 0" here to cover the 114 // possibility of calls to BiasedLocking::enabled() before 115 // BiasedLocking::init(). 116 return _biased_locking_enabled || BiasedLockingStartupDelay == 0; 117 } 118 119 120 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 121 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 122 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 123 if (info != NULL) { 124 return info; 125 } 126 127 info = new GrowableArray<MonitorInfo*>(); 128 129 // It's possible for the thread to not have any Java frames on it, 130 // i.e., if it's the main thread and it's already returned from main() 131 if (thread->has_last_Java_frame()) { 132 RegisterMap rm(thread); 133 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 134 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 135 if (monitors != NULL) { 136 int len = monitors->length(); 137 // Walk monitors youngest to oldest 138 for (int i = len - 1; i >= 0; i--) { 139 MonitorInfo* mon_info = monitors->at(i); 140 if (mon_info->eliminated()) continue; 141 oop owner = mon_info->owner(); 142 if (owner != NULL) { 143 info->append(mon_info); 144 } 145 } 146 } 147 } 148 } 149 150 thread->set_cached_monitor_info(info); 151 return info; 152 } 153 154 155 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL, 156 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization). 157 void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { 158 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 159 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 160 161 markWord mark = obj->mark(); 162 if (!mark.has_bias_pattern()) { 163 if (log_is_enabled(Info, biasedlocking)) { 164 ResourceMark rm; 165 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT 166 ", mark " INTPTR_FORMAT ", type %s" 167 ", requesting thread " INTPTR_FORMAT 168 " because it's no longer biased)", 169 p2i((void *)obj), mark.value(), 170 obj->klass()->external_name(), 171 (intptr_t) requesting_thread); 172 } 173 return; 174 } 175 176 uint age = mark.age(); 177 markWord unbiased_prototype = markWord::prototype().set_age(age); 178 179 // Log at "info" level if not bulk, else "trace" level 180 if (!is_bulk) { 181 ResourceMark rm; 182 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark " 183 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 184 ", requesting thread " INTPTR_FORMAT, 185 p2i((void *)obj), 186 mark.value(), 187 obj->klass()->external_name(), 188 obj->klass()->prototype_header().value(), 189 (intptr_t) requesting_thread); 190 } else { 191 ResourceMark rm; 192 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark " 193 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT 194 " , requesting thread " INTPTR_FORMAT, 195 p2i((void *)obj), 196 mark.value(), 197 obj->klass()->external_name(), 198 obj->klass()->prototype_header().value(), 199 (intptr_t) requesting_thread); 200 } 201 202 JavaThread* biased_thread = mark.biased_locker(); 203 if (biased_thread == NULL) { 204 // Object is anonymously biased. We can get here if, for 205 // example, we revoke the bias due to an identity hash code 206 // being computed for an object. 207 obj->set_mark(unbiased_prototype); 208 209 // Log at "info" level if not bulk, else "trace" level 210 if (!is_bulk) { 211 log_info(biasedlocking)(" Revoked bias of anonymously-biased object"); 212 } else { 213 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object"); 214 } 215 return; 216 } 217 218 // Handle case where the thread toward which the object was biased has exited 219 bool thread_is_alive = false; 220 if (requesting_thread == biased_thread) { 221 thread_is_alive = true; 222 } else { 223 ThreadsListHandle tlh; 224 thread_is_alive = tlh.includes(biased_thread); 225 } 226 if (!thread_is_alive) { 227 obj->set_mark(unbiased_prototype); 228 // Log at "info" level if not bulk, else "trace" level 229 if (!is_bulk) { 230 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread (" 231 PTR_FORMAT ")", p2i(biased_thread)); 232 } else { 233 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread (" 234 PTR_FORMAT ")", p2i(biased_thread)); 235 } 236 return; 237 } 238 239 // Log at "info" level if not bulk, else "trace" level 240 if (!is_bulk) { 241 log_info(biasedlocking)(" Revoked bias of object biased toward live thread (" 242 PTR_FORMAT ")", p2i(biased_thread)); 243 } else { 244 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread (" 245 PTR_FORMAT ")", p2i(biased_thread)); 246 } 247 248 // Thread owning bias is alive. 249 // Check to see whether it currently owns the lock and, if so, 250 // write down the needed displaced headers to the thread's stack. 251 // Otherwise, restore the object's header either to the unlocked 252 // or unbiased state. 253 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 254 BasicLock* highest_lock = NULL; 255 for (int i = 0; i < cached_monitor_info->length(); i++) { 256 MonitorInfo* mon_info = cached_monitor_info->at(i); 257 if (mon_info->owner() == obj) { 258 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 259 p2i((void *) mon_info->owner()), 260 p2i((void *) obj)); 261 // Assume recursive case and fix up highest lock below 262 markWord mark = markWord::encode((BasicLock*) NULL); 263 highest_lock = mon_info->lock(); 264 highest_lock->set_displaced_header(mark); 265 } else { 266 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 267 p2i((void *) mon_info->owner()), 268 p2i((void *) obj)); 269 } 270 } 271 if (highest_lock != NULL) { 272 // Fix up highest lock to contain displaced header and point 273 // object at it 274 highest_lock->set_displaced_header(unbiased_prototype); 275 // Reset object header to point to displaced mark. 276 // Must release store the lock address for platforms without TSO 277 // ordering (e.g. ppc). 278 obj->release_set_mark(markWord::encode(highest_lock)); 279 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 280 // Log at "info" level if not bulk, else "trace" level 281 if (!is_bulk) { 282 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 283 } else { 284 log_trace(biasedlocking)(" Revoked bias of currently-locked object"); 285 } 286 } else { 287 // Log at "info" level if not bulk, else "trace" level 288 if (!is_bulk) { 289 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 290 } else { 291 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object"); 292 } 293 // Store the unlocked value into the object's header. 294 obj->set_mark(unbiased_prototype); 295 } 296 297 // If requested, return information on which thread held the bias 298 if (biased_locker != NULL) { 299 *biased_locker = biased_thread; 300 } 301 } 302 303 304 enum HeuristicsResult { 305 HR_NOT_BIASED = 1, 306 HR_SINGLE_REVOKE = 2, 307 HR_BULK_REBIAS = 3, 308 HR_BULK_REVOKE = 4 309 }; 310 311 312 static HeuristicsResult update_heuristics(oop o) { 313 markWord mark = o->mark(); 314 if (!mark.has_bias_pattern()) { 315 return HR_NOT_BIASED; 316 } 317 318 // Heuristics to attempt to throttle the number of revocations. 319 // Stages: 320 // 1. Revoke the biases of all objects in the heap of this type, 321 // but allow rebiasing of those objects if unlocked. 322 // 2. Revoke the biases of all objects in the heap of this type 323 // and don't allow rebiasing of these objects. Disable 324 // allocation of objects of that type with the bias bit set. 325 Klass* k = o->klass(); 326 jlong cur_time = os::javaTimeMillis(); 327 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 328 int revocation_count = k->biased_lock_revocation_count(); 329 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 330 (revocation_count < BiasedLockingBulkRevokeThreshold) && 331 (last_bulk_revocation_time != 0) && 332 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 333 // This is the first revocation we've seen in a while of an 334 // object of this type since the last time we performed a bulk 335 // rebiasing operation. The application is allocating objects in 336 // bulk which are biased toward a thread and then handing them 337 // off to another thread. We can cope with this allocation 338 // pattern via the bulk rebiasing mechanism so we reset the 339 // klass's revocation count rather than allow it to increase 340 // monotonically. If we see the need to perform another bulk 341 // rebias operation later, we will, and if subsequently we see 342 // many more revocation operations in a short period of time we 343 // will completely disable biasing for this type. 344 k->set_biased_lock_revocation_count(0); 345 revocation_count = 0; 346 } 347 348 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 349 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 350 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 351 } 352 353 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 354 return HR_BULK_REVOKE; 355 } 356 357 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 358 return HR_BULK_REBIAS; 359 } 360 361 return HR_SINGLE_REVOKE; 362 } 363 364 365 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) { 366 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 367 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 368 369 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object " 370 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 371 (bulk_rebias ? "rebias" : "revoke"), 372 p2i((void *) o), 373 o->mark().value(), 374 o->klass()->external_name()); 375 376 jlong cur_time = os::javaTimeMillis(); 377 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 378 379 Klass* k_o = o->klass(); 380 Klass* klass = k_o; 381 382 { 383 JavaThreadIteratorWithHandle jtiwh; 384 385 if (bulk_rebias) { 386 // Use the epoch in the klass of the object to implicitly revoke 387 // all biases of objects of this data type and force them to be 388 // reacquired. However, we also need to walk the stacks of all 389 // threads and update the headers of lightweight locked objects 390 // with biases to have the current epoch. 391 392 // If the prototype header doesn't have the bias pattern, don't 393 // try to update the epoch -- assume another VM operation came in 394 // and reset the header to the unbiased state, which will 395 // implicitly cause all existing biases to be revoked 396 if (klass->prototype_header().has_bias_pattern()) { 397 int prev_epoch = klass->prototype_header().bias_epoch(); 398 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch()); 399 int cur_epoch = klass->prototype_header().bias_epoch(); 400 401 // Now walk all threads' stacks and adjust epochs of any biased 402 // and locked objects of this data type we encounter 403 for (; JavaThread *thr = jtiwh.next(); ) { 404 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 405 for (int i = 0; i < cached_monitor_info->length(); i++) { 406 MonitorInfo* mon_info = cached_monitor_info->at(i); 407 oop owner = mon_info->owner(); 408 markWord mark = owner->mark(); 409 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 410 // We might have encountered this object already in the case of recursive locking 411 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 412 owner->set_mark(mark.set_bias_epoch(cur_epoch)); 413 } 414 } 415 } 416 } 417 418 // At this point we're done. All we have to do is potentially 419 // adjust the header of the given object to revoke its bias. 420 single_revoke_at_safepoint(o, true, requesting_thread, NULL); 421 } else { 422 if (log_is_enabled(Info, biasedlocking)) { 423 ResourceMark rm; 424 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name()); 425 } 426 427 // Disable biased locking for this data type. Not only will this 428 // cause future instances to not be biased, but existing biased 429 // instances will notice that this implicitly caused their biases 430 // to be revoked. 431 klass->set_prototype_header(markWord::prototype()); 432 433 // Now walk all threads' stacks and forcibly revoke the biases of 434 // any locked and biased objects of this data type we encounter. 435 for (; JavaThread *thr = jtiwh.next(); ) { 436 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 437 for (int i = 0; i < cached_monitor_info->length(); i++) { 438 MonitorInfo* mon_info = cached_monitor_info->at(i); 439 oop owner = mon_info->owner(); 440 markWord mark = owner->mark(); 441 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 442 single_revoke_at_safepoint(owner, true, requesting_thread, NULL); 443 } 444 } 445 } 446 447 // Must force the bias of the passed object to be forcibly revoked 448 // as well to ensure guarantees to callers 449 single_revoke_at_safepoint(o, true, requesting_thread, NULL); 450 } 451 } // ThreadsListHandle is destroyed here. 452 453 log_info(biasedlocking)("* Ending bulk revocation"); 454 455 assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation"); 456 } 457 458 459 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) { 460 if (thread != NULL) { 461 thread->set_cached_monitor_info(NULL); 462 } else { 463 // Walk the thread list clearing out the cached monitors 464 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 465 thr->set_cached_monitor_info(NULL); 466 } 467 } 468 } 469 470 471 class VM_BulkRevokeBias : public VM_Operation { 472 private: 473 Handle* _obj; 474 JavaThread* _requesting_thread; 475 bool _bulk_rebias; 476 uint64_t _safepoint_id; 477 478 public: 479 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 480 bool bulk_rebias) 481 : _obj(obj) 482 , _requesting_thread(requesting_thread) 483 , _bulk_rebias(bulk_rebias) 484 , _safepoint_id(0) {} 485 486 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 487 488 virtual void doit() { 489 BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread); 490 _safepoint_id = SafepointSynchronize::safepoint_id(); 491 clean_up_cached_monitor_info(); 492 } 493 494 bool is_bulk_rebias() const { 495 return _bulk_rebias; 496 } 497 498 uint64_t safepoint_id() const { 499 return _safepoint_id; 500 } 501 }; 502 503 504 class RevokeOneBias : public HandshakeClosure { 505 protected: 506 Handle _obj; 507 JavaThread* _requesting_thread; 508 JavaThread* _biased_locker; 509 BiasedLocking::Condition _status_code; 510 traceid _biased_locker_id; 511 512 public: 513 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker) 514 : HandshakeClosure("RevokeOneBias") 515 , _obj(obj) 516 , _requesting_thread(requesting_thread) 517 , _biased_locker(biased_locker) 518 , _status_code(BiasedLocking::NOT_BIASED) 519 , _biased_locker_id(0) {} 520 521 void do_thread(Thread* target) { 522 assert(target == _biased_locker, "Wrong thread"); 523 524 oop o = _obj(); 525 markWord mark = o->mark(); 526 527 if (!mark.has_bias_pattern()) { 528 return; 529 } 530 531 markWord prototype = o->klass()->prototype_header(); 532 if (!prototype.has_bias_pattern()) { 533 // This object has a stale bias from before the handshake 534 // was requested. If we fail this race, the object's bias 535 // has been revoked by another thread so we simply return. 536 markWord biased_value = mark; 537 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 538 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 539 if (biased_value == mark) { 540 _status_code = BiasedLocking::BIAS_REVOKED; 541 } 542 return; 543 } 544 545 if (_biased_locker == mark.biased_locker()) { 546 if (mark.bias_epoch() == prototype.bias_epoch()) { 547 // Epoch is still valid. This means biaser could be currently 548 // synchronized on this object. We must walk its stack looking 549 // for monitor records associated with this object and change 550 // them to be stack locks if any are found. 551 ResourceMark rm; 552 BiasedLocking::walk_stack_and_revoke(o, _biased_locker); 553 _biased_locker->set_cached_monitor_info(NULL); 554 assert(!o->mark().has_bias_pattern(), "invariant"); 555 _biased_locker_id = JFR_THREAD_ID(_biased_locker); 556 _status_code = BiasedLocking::BIAS_REVOKED; 557 return; 558 } else { 559 markWord biased_value = mark; 560 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 561 if (mark == biased_value || !mark.has_bias_pattern()) { 562 assert(!o->mark().has_bias_pattern(), "should be revoked"); 563 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED; 564 return; 565 } 566 } 567 } 568 569 _status_code = BiasedLocking::NOT_REVOKED; 570 } 571 572 BiasedLocking::Condition status_code() const { 573 return _status_code; 574 } 575 576 traceid biased_locker() const { 577 return _biased_locker_id; 578 } 579 }; 580 581 582 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) { 583 assert(event != NULL, "invariant"); 584 assert(k != NULL, "invariant"); 585 assert(event->should_commit(), "invariant"); 586 event->set_lockClass(k); 587 event->commit(); 588 } 589 590 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) { 591 assert(event != NULL, "invariant"); 592 assert(k != NULL, "invariant"); 593 assert(op != NULL, "invariant"); 594 assert(event->should_commit(), "invariant"); 595 event->set_lockClass(k); 596 event->set_safepointId(0); 597 event->set_previousOwner(op->biased_locker()); 598 event->commit(); 599 } 600 601 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) { 602 assert(event != NULL, "invariant"); 603 assert(k != NULL, "invariant"); 604 assert(op != NULL, "invariant"); 605 assert(event->should_commit(), "invariant"); 606 event->set_revokedClass(k); 607 event->set_disableBiasing(!op->is_bulk_rebias()); 608 event->set_safepointId(op->safepoint_id()); 609 event->commit(); 610 } 611 612 613 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) { 614 615 EventBiasedLockRevocation event; 616 if (PrintBiasedLockingStatistics) { 617 Atomic::inc(handshakes_count_addr()); 618 } 619 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread " 620 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester), 621 p2i(biaser), p2i(obj())); 622 623 RevokeOneBias revoke(obj, requester, biaser); 624 bool executed = Handshake::execute(&revoke, biaser); 625 if (revoke.status_code() == NOT_REVOKED) { 626 return NOT_REVOKED; 627 } 628 if (executed) { 629 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked", 630 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already ")); 631 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) { 632 post_revocation_event(&event, obj->klass(), &revoke); 633 } 634 assert(!obj->mark().has_bias_pattern(), "invariant"); 635 return revoke.status_code(); 636 } else { 637 // Thread was not alive. 638 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly 639 // created JavaThread (that happens to get the same memory address as biaser) synchronizing 640 // on this object. 641 { 642 MutexLocker ml(Threads_lock); 643 markWord mark = obj->mark(); 644 // Check if somebody else was able to revoke it before biased thread exited. 645 if (!mark.has_bias_pattern()) { 646 return NOT_BIASED; 647 } 648 ThreadsListHandle tlh; 649 markWord prototype = obj->klass()->prototype_header(); 650 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() && 651 prototype.bias_epoch() == mark.bias_epoch())) { 652 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 653 if (event.should_commit()) { 654 post_revocation_event(&event, obj->klass(), &revoke); 655 } 656 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now"); 657 return BIAS_REVOKED; 658 } 659 } 660 } 661 662 return NOT_REVOKED; 663 } 664 665 666 // Caller should have instantiated a ResourceMark object before calling this method 667 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) { 668 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes, 669 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints"); 670 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread"); 671 672 markWord mark = obj->mark(); 673 assert(mark.biased_locker() == biased_locker && 674 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant"); 675 676 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark " 677 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 678 ", biaser " INTPTR_FORMAT " %s", 679 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread", 680 p2i(Thread::current()), 681 p2i(obj), 682 mark.value(), 683 obj->klass()->external_name(), 684 obj->klass()->prototype_header().value(), 685 p2i(biased_locker), 686 Thread::current()->is_VM_thread() ? "" : "(walking own stack)"); 687 688 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age()); 689 690 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker); 691 BasicLock* highest_lock = NULL; 692 for (int i = 0; i < cached_monitor_info->length(); i++) { 693 MonitorInfo* mon_info = cached_monitor_info->at(i); 694 if (mon_info->owner() == obj) { 695 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 696 p2i(mon_info->owner()), 697 p2i(obj)); 698 // Assume recursive case and fix up highest lock below 699 markWord mark = markWord::encode((BasicLock*) NULL); 700 highest_lock = mon_info->lock(); 701 highest_lock->set_displaced_header(mark); 702 } else { 703 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 704 p2i(mon_info->owner()), 705 p2i(obj)); 706 } 707 } 708 if (highest_lock != NULL) { 709 // Fix up highest lock to contain displaced header and point 710 // object at it 711 highest_lock->set_displaced_header(unbiased_prototype); 712 // Reset object header to point to displaced mark. 713 // Must release store the lock address for platforms without TSO 714 // ordering (e.g. ppc). 715 obj->release_set_mark(markWord::encode(highest_lock)); 716 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 717 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 718 } else { 719 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 720 // Store the unlocked value into the object's header. 721 obj->set_mark(unbiased_prototype); 722 } 723 724 assert(!obj->mark().has_bias_pattern(), "must not be biased"); 725 } 726 727 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) { 728 assert(THREAD->is_Java_thread(), "must be called by a JavaThread"); 729 JavaThread* thread = (JavaThread*)THREAD; 730 731 markWord mark = obj->mark(); 732 733 if (!mark.has_bias_pattern()) { 734 return; 735 } 736 737 Klass *k = obj->klass(); 738 assert(mark.biased_locker() == thread && 739 k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state"); 740 ResourceMark rm; 741 log_info(biasedlocking)("Revoking bias by walking my own stack:"); 742 EventBiasedLockSelfRevocation event; 743 BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread); 744 thread->set_cached_monitor_info(NULL); 745 assert(!obj->mark().has_bias_pattern(), "invariant"); 746 if (event.should_commit()) { 747 post_self_revocation_event(&event, k); 748 } 749 } 750 751 void BiasedLocking::revoke(Handle obj, TRAPS) { 752 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 753 754 while (true) { 755 // We can revoke the biases of anonymously-biased objects 756 // efficiently enough that we should not cause these revocations to 757 // update the heuristics because doing so may cause unwanted bulk 758 // revocations (which are expensive) to occur. 759 markWord mark = obj->mark(); 760 761 if (!mark.has_bias_pattern()) { 762 return; 763 } 764 765 if (mark.is_biased_anonymously()) { 766 // We are probably trying to revoke the bias of this object due to 767 // an identity hash code computation. Try to revoke the bias 768 // without a safepoint. This is possible if we can successfully 769 // compare-and-exchange an unbiased header into the mark word of 770 // the object, meaning that no other thread has raced to acquire 771 // the bias of the object. 772 markWord biased_value = mark; 773 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 774 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark); 775 if (res_mark == biased_value) { 776 return; 777 } 778 mark = res_mark; // Refresh mark with the latest value. 779 } else { 780 Klass* k = obj->klass(); 781 markWord prototype_header = k->prototype_header(); 782 if (!prototype_header.has_bias_pattern()) { 783 // This object has a stale bias from before the bulk revocation 784 // for this data type occurred. It's pointless to update the 785 // heuristics at this point so simply update the header with a 786 // CAS. If we fail this race, the object's bias has been revoked 787 // by another thread so we simply return and let the caller deal 788 // with it. 789 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark); 790 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 791 return; 792 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) { 793 // The epoch of this biasing has expired indicating that the 794 // object is effectively unbiased. We can revoke the bias of this 795 // object efficiently enough with a CAS that we shouldn't update the 796 // heuristics. This is normally done in the assembly code but we 797 // can reach this point due to various points in the runtime 798 // needing to revoke biases. 799 markWord res_mark; 800 markWord biased_value = mark; 801 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 802 res_mark = obj->cas_set_mark(unbiased_prototype, mark); 803 if (res_mark == biased_value) { 804 return; 805 } 806 mark = res_mark; // Refresh mark with the latest value. 807 } 808 } 809 810 HeuristicsResult heuristics = update_heuristics(obj()); 811 if (heuristics == HR_NOT_BIASED) { 812 return; 813 } else if (heuristics == HR_SINGLE_REVOKE) { 814 JavaThread *blt = mark.biased_locker(); 815 assert(blt != NULL, "invariant"); 816 if (blt == THREAD) { 817 // A thread is trying to revoke the bias of an object biased 818 // toward it, again likely due to an identity hash code 819 // computation. We can again avoid a safepoint/handshake in this case 820 // since we are only going to walk our own stack. There are no 821 // races with revocations occurring in other threads because we 822 // reach no safepoints in the revocation path. 823 EventBiasedLockSelfRevocation event; 824 ResourceMark rm; 825 walk_stack_and_revoke(obj(), blt); 826 blt->set_cached_monitor_info(NULL); 827 assert(!obj->mark().has_bias_pattern(), "invariant"); 828 if (event.should_commit()) { 829 post_self_revocation_event(&event, obj->klass()); 830 } 831 return; 832 } else { 833 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt); 834 if (cond != NOT_REVOKED) { 835 return; 836 } 837 } 838 } else { 839 assert((heuristics == HR_BULK_REVOKE) || 840 (heuristics == HR_BULK_REBIAS), "?"); 841 EventBiasedLockClassRevocation event; 842 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD, 843 (heuristics == HR_BULK_REBIAS)); 844 VMThread::execute(&bulk_revoke); 845 if (event.should_commit()) { 846 post_class_revocation_event(&event, obj->klass(), &bulk_revoke); 847 } 848 return; 849 } 850 } 851 } 852 853 // All objects in objs should be locked by biaser 854 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) { 855 bool clean_my_cache = false; 856 for (int i = 0; i < objs->length(); i++) { 857 oop obj = (objs->at(i))(); 858 markWord mark = obj->mark(); 859 if (mark.has_bias_pattern()) { 860 walk_stack_and_revoke(obj, biaser); 861 clean_my_cache = true; 862 } 863 } 864 if (clean_my_cache) { 865 clean_up_cached_monitor_info(biaser); 866 } 867 } 868 869 870 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 871 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 872 oop obj = h_obj(); 873 HeuristicsResult heuristics = update_heuristics(obj); 874 if (heuristics == HR_SINGLE_REVOKE) { 875 JavaThread* biased_locker = NULL; 876 single_revoke_at_safepoint(obj, false, NULL, &biased_locker); 877 if (biased_locker) { 878 clean_up_cached_monitor_info(biased_locker); 879 } 880 } else if ((heuristics == HR_BULK_REBIAS) || 881 (heuristics == HR_BULK_REVOKE)) { 882 bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL); 883 clean_up_cached_monitor_info(); 884 } 885 } 886 887 888 void BiasedLocking::preserve_marks() { 889 if (!UseBiasedLocking) 890 return; 891 892 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 893 894 assert(_preserved_oop_stack == NULL, "double initialization"); 895 assert(_preserved_mark_stack == NULL, "double initialization"); 896 897 // In order to reduce the number of mark words preserved during GC 898 // due to the presence of biased locking, we reinitialize most mark 899 // words to the class's prototype during GC -- even those which have 900 // a currently valid bias owner. One important situation where we 901 // must not clobber a bias is when a biased object is currently 902 // locked. To handle this case we iterate over the currently-locked 903 // monitors in a prepass and, if they are biased, preserve their 904 // mark words here. This should be a relatively small set of objects 905 // especially compared to the number of objects in the heap. 906 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true); 907 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 908 909 ResourceMark rm; 910 Thread* cur = Thread::current(); 911 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) { 912 if (thread->has_last_Java_frame()) { 913 RegisterMap rm(thread); 914 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 915 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 916 if (monitors != NULL) { 917 int len = monitors->length(); 918 // Walk monitors youngest to oldest 919 for (int i = len - 1; i >= 0; i--) { 920 MonitorInfo* mon_info = monitors->at(i); 921 if (mon_info->owner_is_scalar_replaced()) continue; 922 oop owner = mon_info->owner(); 923 if (owner != NULL) { 924 markWord mark = owner->mark(); 925 if (mark.has_bias_pattern()) { 926 _preserved_oop_stack->push(Handle(cur, owner)); 927 _preserved_mark_stack->push(mark); 928 } 929 } 930 } 931 } 932 } 933 } 934 } 935 } 936 937 938 void BiasedLocking::restore_marks() { 939 if (!UseBiasedLocking) 940 return; 941 942 assert(_preserved_oop_stack != NULL, "double free"); 943 assert(_preserved_mark_stack != NULL, "double free"); 944 945 int len = _preserved_oop_stack->length(); 946 for (int i = 0; i < len; i++) { 947 Handle owner = _preserved_oop_stack->at(i); 948 markWord mark = _preserved_mark_stack->at(i); 949 owner->set_mark(mark); 950 } 951 952 delete _preserved_oop_stack; 953 _preserved_oop_stack = NULL; 954 delete _preserved_mark_stack; 955 _preserved_mark_stack = NULL; 956 } 957 958 959 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 960 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 961 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 962 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 963 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 964 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); } 965 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 966 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 967 968 969 // BiasedLockingCounters 970 971 int BiasedLockingCounters::slow_path_entry_count() const { 972 if (_slow_path_entry_count != 0) { 973 return _slow_path_entry_count; 974 } 975 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 976 _rebiased_lock_entry_count + _revoked_lock_entry_count + 977 _fast_path_entry_count; 978 979 return _total_entry_count - sum; 980 } 981 982 void BiasedLockingCounters::print_on(outputStream* st) const { 983 tty->print_cr("# total entries: %d", _total_entry_count); 984 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 985 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 986 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 987 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 988 tty->print_cr("# handshakes entries: %d", _handshakes_count); 989 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 990 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 991 } 992 993 void BiasedLockingCounters::print() const { print_on(tty); }