biasedLocking.cpp revision 0:a61af66fc99e
1 2/* 3 * Copyright 2005-2007 Sun Microsystems, Inc. All Rights Reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 21 * CA 95054 USA or visit www.sun.com if you need additional information or 22 * have any questions. 23 * 24 */ 25 26# include "incls/_precompiled.incl" 27# include "incls/_biasedLocking.cpp.incl" 28 29static bool _biased_locking_enabled = false; 30BiasedLockingCounters BiasedLocking::_counters; 31 32static GrowableArray<Handle>* _preserved_oop_stack = NULL; 33static GrowableArray<markOop>* _preserved_mark_stack = NULL; 34 35static void enable_biased_locking(klassOop k) { 36 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype()); 37} 38 39class VM_EnableBiasedLocking: public VM_Operation { 40 public: 41 VM_EnableBiasedLocking() {} 42 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 43 void doit() { 44 // Iterate the system dictionary enabling biased locking for all 45 // currently loaded classes 46 SystemDictionary::classes_do(enable_biased_locking); 47 // Indicate that future instances should enable it as well 48 _biased_locking_enabled = true; 49 50 if (TraceBiasedLocking) { 51 tty->print_cr("Biased locking enabled"); 52 } 53 } 54 55 bool allow_nested_vm_operations() const { return false; } 56}; 57 58 59// One-shot PeriodicTask subclass for enabling biased locking 60class EnableBiasedLockingTask : public PeriodicTask { 61 public: 62 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 63 64 virtual void task() { 65 VM_EnableBiasedLocking op; 66 VMThread::execute(&op); 67 68 // Reclaim our storage and disenroll ourself 69 delete this; 70 } 71}; 72 73 74void BiasedLocking::init() { 75 // If biased locking is enabled, schedule a task to fire a few 76 // seconds into the run which turns on biased locking for all 77 // currently loaded classes as well as future ones. This is a 78 // workaround for startup time regressions due to a large number of 79 // safepoints being taken during VM startup for bias revocation. 80 // Ideally we would have a lower cost for individual bias revocation 81 // and not need a mechanism like this. 82 if (UseBiasedLocking) { 83 if (BiasedLockingStartupDelay > 0) { 84 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 85 task->enroll(); 86 } else { 87 VM_EnableBiasedLocking op; 88 VMThread::execute(&op); 89 } 90 } 91} 92 93 94bool BiasedLocking::enabled() { 95 return _biased_locking_enabled; 96} 97 98// Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 99static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 100 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 101 if (info != NULL) { 102 return info; 103 } 104 105 info = new GrowableArray<MonitorInfo*>(); 106 107 // It's possible for the thread to not have any Java frames on it, 108 // i.e., if it's the main thread and it's already returned from main() 109 if (thread->has_last_Java_frame()) { 110 RegisterMap rm(thread); 111 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 112 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 113 if (monitors != NULL) { 114 int len = monitors->length(); 115 // Walk monitors youngest to oldest 116 for (int i = len - 1; i >= 0; i--) { 117 MonitorInfo* mon_info = monitors->at(i); 118 oop owner = mon_info->owner(); 119 if (owner != NULL) { 120 info->append(mon_info); 121 } 122 } 123 } 124 } 125 } 126 127 thread->set_cached_monitor_info(info); 128 return info; 129} 130 131 132static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { 133 markOop mark = obj->mark(); 134 if (!mark->has_bias_pattern()) { 135 if (TraceBiasedLocking) { 136 ResourceMark rm; 137 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", 138 Klass::cast(obj->klass())->external_name()); 139 } 140 return BiasedLocking::NOT_BIASED; 141 } 142 143 int age = mark->age(); 144 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); 145 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); 146 147 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 148 ResourceMark rm; 149 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT, 150 (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); 151 } 152 153 JavaThread* biased_thread = mark->biased_locker(); 154 if (biased_thread == NULL) { 155 // Object is anonymously biased. We can get here if, for 156 // example, we revoke the bias due to an identity hash code 157 // being computed for an object. 158 if (!allow_rebias) { 159 obj->set_mark(unbiased_prototype); 160 } 161 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 162 tty->print_cr(" Revoked bias of anonymously-biased object"); 163 } 164 return BiasedLocking::BIAS_REVOKED; 165 } 166 167 // Handle case where the thread toward which the object was biased has exited 168 bool thread_is_alive = false; 169 if (requesting_thread == biased_thread) { 170 thread_is_alive = true; 171 } else { 172 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { 173 if (cur_thread == biased_thread) { 174 thread_is_alive = true; 175 break; 176 } 177 } 178 } 179 if (!thread_is_alive) { 180 if (allow_rebias) { 181 obj->set_mark(biased_prototype); 182 } else { 183 obj->set_mark(unbiased_prototype); 184 } 185 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 186 tty->print_cr(" Revoked bias of object biased toward dead thread"); 187 } 188 return BiasedLocking::BIAS_REVOKED; 189 } 190 191 // Thread owning bias is alive. 192 // Check to see whether it currently owns the lock and, if so, 193 // write down the needed displaced headers to the thread's stack. 194 // Otherwise, restore the object's header either to the unlocked 195 // or unbiased state. 196 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 197 BasicLock* highest_lock = NULL; 198 for (int i = 0; i < cached_monitor_info->length(); i++) { 199 MonitorInfo* mon_info = cached_monitor_info->at(i); 200 if (mon_info->owner() == obj) { 201 if (TraceBiasedLocking && Verbose) { 202 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 203 (intptr_t) mon_info->owner(), 204 (intptr_t) obj); 205 } 206 // Assume recursive case and fix up highest lock later 207 markOop mark = markOopDesc::encode((BasicLock*) NULL); 208 highest_lock = mon_info->lock(); 209 highest_lock->set_displaced_header(mark); 210 } else { 211 if (TraceBiasedLocking && Verbose) { 212 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 213 (intptr_t) mon_info->owner(), 214 (intptr_t) obj); 215 } 216 } 217 } 218 if (highest_lock != NULL) { 219 // Fix up highest lock to contain displaced header and point 220 // object at it 221 highest_lock->set_displaced_header(unbiased_prototype); 222 // Reset object header to point to displaced mark 223 obj->set_mark(markOopDesc::encode(highest_lock)); 224 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 225 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 226 tty->print_cr(" Revoked bias of currently-locked object"); 227 } 228 } else { 229 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 230 tty->print_cr(" Revoked bias of currently-unlocked object"); 231 } 232 if (allow_rebias) { 233 obj->set_mark(biased_prototype); 234 } else { 235 // Store the unlocked value into the object's header. 236 obj->set_mark(unbiased_prototype); 237 } 238 } 239 240 return BiasedLocking::BIAS_REVOKED; 241} 242 243 244enum HeuristicsResult { 245 HR_NOT_BIASED = 1, 246 HR_SINGLE_REVOKE = 2, 247 HR_BULK_REBIAS = 3, 248 HR_BULK_REVOKE = 4 249}; 250 251 252static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { 253 markOop mark = o->mark(); 254 if (!mark->has_bias_pattern()) { 255 return HR_NOT_BIASED; 256 } 257 258 // Heuristics to attempt to throttle the number of revocations. 259 // Stages: 260 // 1. Revoke the biases of all objects in the heap of this type, 261 // but allow rebiasing of those objects if unlocked. 262 // 2. Revoke the biases of all objects in the heap of this type 263 // and don't allow rebiasing of these objects. Disable 264 // allocation of objects of that type with the bias bit set. 265 Klass* k = o->blueprint(); 266 jlong cur_time = os::javaTimeMillis(); 267 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 268 int revocation_count = k->biased_lock_revocation_count(); 269 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 270 (revocation_count < BiasedLockingBulkRevokeThreshold) && 271 (last_bulk_revocation_time != 0) && 272 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 273 // This is the first revocation we've seen in a while of an 274 // object of this type since the last time we performed a bulk 275 // rebiasing operation. The application is allocating objects in 276 // bulk which are biased toward a thread and then handing them 277 // off to another thread. We can cope with this allocation 278 // pattern via the bulk rebiasing mechanism so we reset the 279 // klass's revocation count rather than allow it to increase 280 // monotonically. If we see the need to perform another bulk 281 // rebias operation later, we will, and if subsequently we see 282 // many more revocation operations in a short period of time we 283 // will completely disable biasing for this type. 284 k->set_biased_lock_revocation_count(0); 285 revocation_count = 0; 286 } 287 288 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 289 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 290 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 291 } 292 293 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 294 return HR_BULK_REVOKE; 295 } 296 297 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 298 return HR_BULK_REBIAS; 299 } 300 301 return HR_SINGLE_REVOKE; 302} 303 304 305static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, 306 bool bulk_rebias, 307 bool attempt_rebias_of_object, 308 JavaThread* requesting_thread) { 309 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 310 311 if (TraceBiasedLocking) { 312 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " 313 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 314 (bulk_rebias ? "rebias" : "revoke"), 315 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name()); 316 } 317 318 jlong cur_time = os::javaTimeMillis(); 319 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time); 320 321 322 klassOop k_o = o->klass(); 323 Klass* klass = Klass::cast(k_o); 324 325 if (bulk_rebias) { 326 // Use the epoch in the klass of the object to implicitly revoke 327 // all biases of objects of this data type and force them to be 328 // reacquired. However, we also need to walk the stacks of all 329 // threads and update the headers of lightweight locked objects 330 // with biases to have the current epoch. 331 332 // If the prototype header doesn't have the bias pattern, don't 333 // try to update the epoch -- assume another VM operation came in 334 // and reset the header to the unbiased state, which will 335 // implicitly cause all existing biases to be revoked 336 if (klass->prototype_header()->has_bias_pattern()) { 337 int prev_epoch = klass->prototype_header()->bias_epoch(); 338 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); 339 int cur_epoch = klass->prototype_header()->bias_epoch(); 340 341 // Now walk all threads' stacks and adjust epochs of any biased 342 // and locked objects of this data type we encounter 343 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 344 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 345 for (int i = 0; i < cached_monitor_info->length(); i++) { 346 MonitorInfo* mon_info = cached_monitor_info->at(i); 347 oop owner = mon_info->owner(); 348 markOop mark = owner->mark(); 349 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 350 // We might have encountered this object already in the case of recursive locking 351 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 352 owner->set_mark(mark->set_bias_epoch(cur_epoch)); 353 } 354 } 355 } 356 } 357 358 // At this point we're done. All we have to do is potentially 359 // adjust the header of the given object to revoke its bias. 360 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); 361 } else { 362 if (TraceBiasedLocking) { 363 ResourceMark rm; 364 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); 365 } 366 367 // Disable biased locking for this data type. Not only will this 368 // cause future instances to not be biased, but existing biased 369 // instances will notice that this implicitly caused their biases 370 // to be revoked. 371 klass->set_prototype_header(markOopDesc::prototype()); 372 373 // Now walk all threads' stacks and forcibly revoke the biases of 374 // any locked and biased objects of this data type we encounter. 375 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 376 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 377 for (int i = 0; i < cached_monitor_info->length(); i++) { 378 MonitorInfo* mon_info = cached_monitor_info->at(i); 379 oop owner = mon_info->owner(); 380 markOop mark = owner->mark(); 381 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 382 revoke_bias(owner, false, true, requesting_thread); 383 } 384 } 385 } 386 387 // Must force the bias of the passed object to be forcibly revoked 388 // as well to ensure guarantees to callers 389 revoke_bias(o, false, true, requesting_thread); 390 } 391 392 if (TraceBiasedLocking) { 393 tty->print_cr("* Ending bulk revocation"); 394 } 395 396 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; 397 398 if (attempt_rebias_of_object && 399 o->mark()->has_bias_pattern() && 400 klass->prototype_header()->has_bias_pattern()) { 401 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), 402 klass->prototype_header()->bias_epoch()); 403 o->set_mark(new_mark); 404 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; 405 if (TraceBiasedLocking) { 406 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 407 } 408 } 409 410 assert(!o->mark()->has_bias_pattern() || 411 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), 412 "bug in bulk bias revocation"); 413 414 return status_code; 415} 416 417 418static void clean_up_cached_monitor_info() { 419 // Walk the thread list clearing out the cached monitors 420 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 421 thr->set_cached_monitor_info(NULL); 422 } 423} 424 425 426class VM_RevokeBias : public VM_Operation { 427protected: 428 Handle* _obj; 429 GrowableArray<Handle>* _objs; 430 JavaThread* _requesting_thread; 431 BiasedLocking::Condition _status_code; 432 433public: 434 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) 435 : _obj(obj) 436 , _objs(NULL) 437 , _requesting_thread(requesting_thread) 438 , _status_code(BiasedLocking::NOT_BIASED) {} 439 440 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) 441 : _obj(NULL) 442 , _objs(objs) 443 , _requesting_thread(requesting_thread) 444 , _status_code(BiasedLocking::NOT_BIASED) {} 445 446 virtual VMOp_Type type() const { return VMOp_RevokeBias; } 447 448 virtual bool doit_prologue() { 449 // Verify that there is actual work to do since the callers just 450 // give us locked object(s). If we don't find any biased objects 451 // there is nothing to do and we avoid a safepoint. 452 if (_obj != NULL) { 453 markOop mark = (*_obj)()->mark(); 454 if (mark->has_bias_pattern()) { 455 return true; 456 } 457 } else { 458 for ( int i = 0 ; i < _objs->length(); i++ ) { 459 markOop mark = (_objs->at(i))()->mark(); 460 if (mark->has_bias_pattern()) { 461 return true; 462 } 463 } 464 } 465 return false; 466 } 467 468 virtual void doit() { 469 if (_obj != NULL) { 470 if (TraceBiasedLocking) { 471 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); 472 } 473 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); 474 clean_up_cached_monitor_info(); 475 return; 476 } else { 477 if (TraceBiasedLocking) { 478 tty->print_cr("Revoking bias with global safepoint:"); 479 } 480 BiasedLocking::revoke_at_safepoint(_objs); 481 } 482 } 483 484 BiasedLocking::Condition status_code() const { 485 return _status_code; 486 } 487}; 488 489 490class VM_BulkRevokeBias : public VM_RevokeBias { 491private: 492 bool _bulk_rebias; 493 bool _attempt_rebias_of_object; 494 495public: 496 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 497 bool bulk_rebias, 498 bool attempt_rebias_of_object) 499 : VM_RevokeBias(obj, requesting_thread) 500 , _bulk_rebias(bulk_rebias) 501 , _attempt_rebias_of_object(attempt_rebias_of_object) {} 502 503 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 504 virtual bool doit_prologue() { return true; } 505 506 virtual void doit() { 507 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 508 clean_up_cached_monitor_info(); 509 } 510}; 511 512 513BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 514 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 515 516 // We can revoke the biases of anonymously-biased objects 517 // efficiently enough that we should not cause these revocations to 518 // update the heuristics because doing so may cause unwanted bulk 519 // revocations (which are expensive) to occur. 520 markOop mark = obj->mark(); 521 if (mark->is_biased_anonymously() && !attempt_rebias) { 522 // We are probably trying to revoke the bias of this object due to 523 // an identity hash code computation. Try to revoke the bias 524 // without a safepoint. This is possible if we can successfully 525 // compare-and-exchange an unbiased header into the mark word of 526 // the object, meaning that no other thread has raced to acquire 527 // the bias of the object. 528 markOop biased_value = mark; 529 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 530 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 531 if (res_mark == biased_value) { 532 return BIAS_REVOKED; 533 } 534 } else if (mark->has_bias_pattern()) { 535 Klass* k = Klass::cast(obj->klass()); 536 markOop prototype_header = k->prototype_header(); 537 if (!prototype_header->has_bias_pattern()) { 538 // This object has a stale bias from before the bulk revocation 539 // for this data type occurred. It's pointless to update the 540 // heuristics at this point so simply update the header with a 541 // CAS. If we fail this race, the object's bias has been revoked 542 // by another thread so we simply return and let the caller deal 543 // with it. 544 markOop biased_value = mark; 545 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); 546 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); 547 return BIAS_REVOKED; 548 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { 549 // The epoch of this biasing has expired indicating that the 550 // object is effectively unbiased. Depending on whether we need 551 // to rebias or revoke the bias of this object we can do it 552 // efficiently enough with a CAS that we shouldn't update the 553 // heuristics. This is normally done in the assembly code but we 554 // can reach this point due to various points in the runtime 555 // needing to revoke biases. 556 if (attempt_rebias) { 557 assert(THREAD->is_Java_thread(), ""); 558 markOop biased_value = mark; 559 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); 560 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); 561 if (res_mark == biased_value) { 562 return BIAS_REVOKED_AND_REBIASED; 563 } 564 } else { 565 markOop biased_value = mark; 566 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 567 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 568 if (res_mark == biased_value) { 569 return BIAS_REVOKED; 570 } 571 } 572 } 573 } 574 575 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); 576 if (heuristics == HR_NOT_BIASED) { 577 return NOT_BIASED; 578 } else if (heuristics == HR_SINGLE_REVOKE) { 579 if (mark->biased_locker() == THREAD) { 580 // A thread is trying to revoke the bias of an object biased 581 // toward it, again likely due to an identity hash code 582 // computation. We can again avoid a safepoint in this case 583 // since we are only going to walk our own stack. There are no 584 // races with revocations occurring in other threads because we 585 // reach no safepoints in the revocation path. 586 ResourceMark rm; 587 if (TraceBiasedLocking) { 588 tty->print_cr("Revoking bias by walking my own stack:"); 589 } 590 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); 591 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); 592 assert(cond == BIAS_REVOKED, "why not?"); 593 return cond; 594 } else { 595 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); 596 VMThread::execute(&revoke); 597 return revoke.status_code(); 598 } 599 } 600 601 assert((heuristics == HR_BULK_REVOKE) || 602 (heuristics == HR_BULK_REBIAS), "?"); 603 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, 604 (heuristics == HR_BULK_REBIAS), 605 attempt_rebias); 606 VMThread::execute(&bulk_revoke); 607 return bulk_revoke.status_code(); 608} 609 610 611void BiasedLocking::revoke(GrowableArray<Handle>* objs) { 612 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 613 if (objs->length() == 0) { 614 return; 615 } 616 VM_RevokeBias revoke(objs, JavaThread::current()); 617 VMThread::execute(&revoke); 618} 619 620 621void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 622 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 623 oop obj = h_obj(); 624 HeuristicsResult heuristics = update_heuristics(obj, false); 625 if (heuristics == HR_SINGLE_REVOKE) { 626 revoke_bias(obj, false, false, NULL); 627 } else if ((heuristics == HR_BULK_REBIAS) || 628 (heuristics == HR_BULK_REVOKE)) { 629 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 630 } 631 clean_up_cached_monitor_info(); 632} 633 634 635void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 636 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 637 int len = objs->length(); 638 for (int i = 0; i < len; i++) { 639 oop obj = (objs->at(i))(); 640 HeuristicsResult heuristics = update_heuristics(obj, false); 641 if (heuristics == HR_SINGLE_REVOKE) { 642 revoke_bias(obj, false, false, NULL); 643 } else if ((heuristics == HR_BULK_REBIAS) || 644 (heuristics == HR_BULK_REVOKE)) { 645 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 646 } 647 } 648 clean_up_cached_monitor_info(); 649} 650 651 652void BiasedLocking::preserve_marks() { 653 if (!UseBiasedLocking) 654 return; 655 656 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 657 658 assert(_preserved_oop_stack == NULL, "double initialization"); 659 assert(_preserved_mark_stack == NULL, "double initialization"); 660 661 // In order to reduce the number of mark words preserved during GC 662 // due to the presence of biased locking, we reinitialize most mark 663 // words to the class's prototype during GC -- even those which have 664 // a currently valid bias owner. One important situation where we 665 // must not clobber a bias is when a biased object is currently 666 // locked. To handle this case we iterate over the currently-locked 667 // monitors in a prepass and, if they are biased, preserve their 668 // mark words here. This should be a relatively small set of objects 669 // especially compared to the number of objects in the heap. 670 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true); 671 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true); 672 673 ResourceMark rm; 674 Thread* cur = Thread::current(); 675 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { 676 if (thread->has_last_Java_frame()) { 677 RegisterMap rm(thread); 678 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 679 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 680 if (monitors != NULL) { 681 int len = monitors->length(); 682 // Walk monitors youngest to oldest 683 for (int i = len - 1; i >= 0; i--) { 684 MonitorInfo* mon_info = monitors->at(i); 685 oop owner = mon_info->owner(); 686 if (owner != NULL) { 687 markOop mark = owner->mark(); 688 if (mark->has_bias_pattern()) { 689 _preserved_oop_stack->push(Handle(cur, owner)); 690 _preserved_mark_stack->push(mark); 691 } 692 } 693 } 694 } 695 } 696 } 697 } 698} 699 700 701void BiasedLocking::restore_marks() { 702 if (!UseBiasedLocking) 703 return; 704 705 assert(_preserved_oop_stack != NULL, "double free"); 706 assert(_preserved_mark_stack != NULL, "double free"); 707 708 int len = _preserved_oop_stack->length(); 709 for (int i = 0; i < len; i++) { 710 Handle owner = _preserved_oop_stack->at(i); 711 markOop mark = _preserved_mark_stack->at(i); 712 owner->set_mark(mark); 713 } 714 715 delete _preserved_oop_stack; 716 _preserved_oop_stack = NULL; 717 delete _preserved_mark_stack; 718 _preserved_mark_stack = NULL; 719} 720 721 722int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 723int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 724int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 725int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 726int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 727int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 728int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 729 730 731// BiasedLockingCounters 732 733int BiasedLockingCounters::slow_path_entry_count() { 734 if (_slow_path_entry_count != 0) { 735 return _slow_path_entry_count; 736 } 737 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 738 _rebiased_lock_entry_count + _revoked_lock_entry_count + 739 _fast_path_entry_count; 740 741 return _total_entry_count - sum; 742} 743 744void BiasedLockingCounters::print_on(outputStream* st) { 745 tty->print_cr("# total entries: %d", _total_entry_count); 746 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 747 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 748 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 749 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 750 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 751 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 752} 753