1 /* 2 * Copyright (c) 2005, 2012, 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 "oops/klass.inline.hpp" 27 #include "oops/markOop.hpp" 28 #include "runtime/basicLock.hpp" 29 #include "runtime/biasedLocking.hpp" 30 #include "runtime/task.hpp" 31 #include "runtime/vframe.hpp" 32 #include "runtime/vmThread.hpp" 33 #include "runtime/vm_operations.hpp" 34 35 static bool _biased_locking_enabled = false; 36 BiasedLockingCounters BiasedLocking::_counters; 37 38 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 39 static GrowableArray<markOop>* _preserved_mark_stack = NULL; 40 41 static void enable_biased_locking(Klass* k) { 42 k->set_prototype_header(markOopDesc::biased_locking_prototype()); 43 } 44 45 class VM_EnableBiasedLocking: public VM_Operation { 46 private: 47 bool _is_cheap_allocated; 48 public: 49 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } 50 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 51 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } 52 bool is_cheap_allocated() const { return _is_cheap_allocated; } 53 54 void doit() { 55 // Iterate the system dictionary enabling biased locking for all 56 // currently loaded classes 57 SystemDictionary::classes_do(enable_biased_locking); 58 // Indicate that future instances should enable it as well 59 _biased_locking_enabled = true; 60 61 if (TraceBiasedLocking) { 62 tty->print_cr("Biased locking enabled"); 63 } 64 } 65 66 bool allow_nested_vm_operations() const { return false; } 67 }; 68 69 70 // One-shot PeriodicTask subclass for enabling biased locking 71 class EnableBiasedLockingTask : public PeriodicTask { 72 public: 73 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 74 75 virtual void task() { 76 // Use async VM operation to avoid blocking the Watcher thread. 77 // VM Thread will free C heap storage. 78 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); 79 VMThread::execute(op); 80 81 // Reclaim our storage and disenroll ourself 82 delete this; 83 } 84 }; 85 86 87 void BiasedLocking::init() { 88 // If biased locking is enabled, schedule a task to fire a few 89 // seconds into the run which turns on biased locking for all 90 // currently loaded classes as well as future ones. This is a 91 // workaround for startup time regressions due to a large number of 92 // safepoints being taken during VM startup for bias revocation. 93 // Ideally we would have a lower cost for individual bias revocation 94 // and not need a mechanism like this. 95 if (UseBiasedLocking) { 96 if (BiasedLockingStartupDelay > 0) { 97 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 98 task->enroll(); 99 } else { 100 VM_EnableBiasedLocking op(false); 101 VMThread::execute(&op); 102 } 103 } 104 } 105 106 107 bool BiasedLocking::enabled() { 108 return _biased_locking_enabled; 109 } 110 111 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 112 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 113 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 114 if (info != NULL) { 115 return info; 116 } 117 118 info = new GrowableArray<MonitorInfo*>(); 119 120 // It's possible for the thread to not have any Java frames on it, 121 // i.e., if it's the main thread and it's already returned from main() 122 if (thread->has_last_Java_frame()) { 123 RegisterMap rm(thread); 124 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 125 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 126 if (monitors != NULL) { 127 int len = monitors->length(); 128 // Walk monitors youngest to oldest 129 for (int i = len - 1; i >= 0; i--) { 130 MonitorInfo* mon_info = monitors->at(i); 131 if (mon_info->owner_is_scalar_replaced()) continue; 132 oop owner = mon_info->owner(); 133 if (owner != NULL) { 134 info->append(mon_info); 135 } 136 } 137 } 138 } 139 } 140 141 thread->set_cached_monitor_info(info); 142 return info; 143 } 144 145 146 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { 147 markOop mark = obj->mark(); 148 if (!mark->has_bias_pattern()) { 149 if (TraceBiasedLocking) { 150 ResourceMark rm; 151 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", 152 obj->klass()->external_name()); 153 } 154 return BiasedLocking::NOT_BIASED; 155 } 156 157 uint age = mark->age(); 158 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); 159 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); 160 161 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 162 ResourceMark rm; 163 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, 164 (intptr_t) obj, (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); 165 } 166 167 JavaThread* biased_thread = mark->biased_locker(); 168 if (biased_thread == NULL) { 169 // Object is anonymously biased. We can get here if, for 170 // example, we revoke the bias due to an identity hash code 171 // being computed for an object. 172 if (!allow_rebias) { 173 obj->set_mark(unbiased_prototype); 174 } 175 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 176 tty->print_cr(" Revoked bias of anonymously-biased object"); 177 } 178 return BiasedLocking::BIAS_REVOKED; 179 } 180 181 // Handle case where the thread toward which the object was biased has exited 182 bool thread_is_alive = false; 183 if (requesting_thread == biased_thread) { 184 thread_is_alive = true; 185 } else { 186 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { 187 if (cur_thread == biased_thread) { 188 thread_is_alive = true; 189 break; 190 } 191 } 192 } 193 if (!thread_is_alive) { 194 if (allow_rebias) { 195 obj->set_mark(biased_prototype); 196 } else { 197 obj->set_mark(unbiased_prototype); 198 } 199 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 200 tty->print_cr(" Revoked bias of object biased toward dead thread"); 201 } 202 return BiasedLocking::BIAS_REVOKED; 203 } 204 205 // Thread owning bias is alive. 206 // Check to see whether it currently owns the lock and, if so, 207 // write down the needed displaced headers to the thread's stack. 208 // Otherwise, restore the object's header either to the unlocked 209 // or unbiased state. 210 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 211 BasicLock* highest_lock = NULL; 212 for (int i = 0; i < cached_monitor_info->length(); i++) { 213 MonitorInfo* mon_info = cached_monitor_info->at(i); 214 if (mon_info->owner() == obj) { 215 if (TraceBiasedLocking && Verbose) { 216 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 217 (intptr_t) mon_info->owner(), 218 (intptr_t) obj); 219 } 220 // Assume recursive case and fix up highest lock later 221 markOop mark = markOopDesc::encode((BasicLock*) NULL); 222 highest_lock = mon_info->lock(); 223 highest_lock->set_displaced_header(mark); 224 } else { 225 if (TraceBiasedLocking && Verbose) { 226 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 227 (intptr_t) mon_info->owner(), 228 (intptr_t) obj); 229 } 230 } 231 } 232 if (highest_lock != NULL) { 233 // Fix up highest lock to contain displaced header and point 234 // object at it 235 highest_lock->set_displaced_header(unbiased_prototype); 236 // Reset object header to point to displaced mark 237 obj->set_mark(markOopDesc::encode(highest_lock)); 238 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 239 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 240 tty->print_cr(" Revoked bias of currently-locked object"); 241 } 242 } else { 243 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 244 tty->print_cr(" Revoked bias of currently-unlocked object"); 245 } 246 if (allow_rebias) { 247 obj->set_mark(biased_prototype); 248 } else { 249 // Store the unlocked value into the object's header. 250 obj->set_mark(unbiased_prototype); 251 } 252 } 253 254 return BiasedLocking::BIAS_REVOKED; 255 } 256 257 258 enum HeuristicsResult { 259 HR_NOT_BIASED = 1, 260 HR_SINGLE_REVOKE = 2, 261 HR_BULK_REBIAS = 3, 262 HR_BULK_REVOKE = 4 263 }; 264 265 266 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { 267 markOop mark = o->mark(); 268 if (!mark->has_bias_pattern()) { 269 return HR_NOT_BIASED; 270 } 271 272 // Heuristics to attempt to throttle the number of revocations. 273 // Stages: 274 // 1. Revoke the biases of all objects in the heap of this type, 275 // but allow rebiasing of those objects if unlocked. 276 // 2. Revoke the biases of all objects in the heap of this type 277 // and don't allow rebiasing of these objects. Disable 278 // allocation of objects of that type with the bias bit set. 279 Klass* k = o->klass(); 280 jlong cur_time = os::javaTimeMillis(); 281 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 282 int revocation_count = k->biased_lock_revocation_count(); 283 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 284 (revocation_count < BiasedLockingBulkRevokeThreshold) && 285 (last_bulk_revocation_time != 0) && 286 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 287 // This is the first revocation we've seen in a while of an 288 // object of this type since the last time we performed a bulk 289 // rebiasing operation. The application is allocating objects in 290 // bulk which are biased toward a thread and then handing them 291 // off to another thread. We can cope with this allocation 292 // pattern via the bulk rebiasing mechanism so we reset the 293 // klass's revocation count rather than allow it to increase 294 // monotonically. If we see the need to perform another bulk 295 // rebias operation later, we will, and if subsequently we see 296 // many more revocation operations in a short period of time we 297 // will completely disable biasing for this type. 298 k->set_biased_lock_revocation_count(0); 299 revocation_count = 0; 300 } 301 302 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 303 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 304 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 305 } 306 307 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 308 return HR_BULK_REVOKE; 309 } 310 311 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 312 return HR_BULK_REBIAS; 313 } 314 315 return HR_SINGLE_REVOKE; 316 } 317 318 319 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, 320 bool bulk_rebias, 321 bool attempt_rebias_of_object, 322 JavaThread* requesting_thread) { 323 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 324 325 if (TraceBiasedLocking) { 326 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " 327 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 328 (bulk_rebias ? "rebias" : "revoke"), 329 (intptr_t) o, (intptr_t) o->mark(), o->klass()->external_name()); 330 } 331 332 jlong cur_time = os::javaTimeMillis(); 333 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 334 335 336 Klass* k_o = o->klass(); 337 Klass* klass = k_o; 338 339 if (bulk_rebias) { 340 // Use the epoch in the klass of the object to implicitly revoke 341 // all biases of objects of this data type and force them to be 342 // reacquired. However, we also need to walk the stacks of all 343 // threads and update the headers of lightweight locked objects 344 // with biases to have the current epoch. 345 346 // If the prototype header doesn't have the bias pattern, don't 347 // try to update the epoch -- assume another VM operation came in 348 // and reset the header to the unbiased state, which will 349 // implicitly cause all existing biases to be revoked 350 if (klass->prototype_header()->has_bias_pattern()) { 351 int prev_epoch = klass->prototype_header()->bias_epoch(); 352 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); 353 int cur_epoch = klass->prototype_header()->bias_epoch(); 354 355 // Now walk all threads' stacks and adjust epochs of any biased 356 // and locked objects of this data type we encounter 357 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 358 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 359 for (int i = 0; i < cached_monitor_info->length(); i++) { 360 MonitorInfo* mon_info = cached_monitor_info->at(i); 361 oop owner = mon_info->owner(); 362 markOop mark = owner->mark(); 363 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 364 // We might have encountered this object already in the case of recursive locking 365 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 366 owner->set_mark(mark->set_bias_epoch(cur_epoch)); 367 } 368 } 369 } 370 } 371 372 // At this point we're done. All we have to do is potentially 373 // adjust the header of the given object to revoke its bias. 374 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); 375 } else { 376 if (TraceBiasedLocking) { 377 ResourceMark rm; 378 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); 379 } 380 381 // Disable biased locking for this data type. Not only will this 382 // cause future instances to not be biased, but existing biased 383 // instances will notice that this implicitly caused their biases 384 // to be revoked. 385 klass->set_prototype_header(markOopDesc::prototype()); 386 387 // Now walk all threads' stacks and forcibly revoke the biases of 388 // any locked and biased objects of this data type we encounter. 389 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 390 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 391 for (int i = 0; i < cached_monitor_info->length(); i++) { 392 MonitorInfo* mon_info = cached_monitor_info->at(i); 393 oop owner = mon_info->owner(); 394 markOop mark = owner->mark(); 395 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 396 revoke_bias(owner, false, true, requesting_thread); 397 } 398 } 399 } 400 401 // Must force the bias of the passed object to be forcibly revoked 402 // as well to ensure guarantees to callers 403 revoke_bias(o, false, true, requesting_thread); 404 } 405 406 if (TraceBiasedLocking) { 407 tty->print_cr("* Ending bulk revocation"); 408 } 409 410 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; 411 412 if (attempt_rebias_of_object && 413 o->mark()->has_bias_pattern() && 414 klass->prototype_header()->has_bias_pattern()) { 415 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), 416 klass->prototype_header()->bias_epoch()); 417 o->set_mark(new_mark); 418 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; 419 if (TraceBiasedLocking) { 420 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 421 } 422 } 423 424 assert(!o->mark()->has_bias_pattern() || 425 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), 426 "bug in bulk bias revocation"); 427 428 return status_code; 429 } 430 431 432 static void clean_up_cached_monitor_info() { 433 // Walk the thread list clearing out the cached monitors 434 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 435 thr->set_cached_monitor_info(NULL); 436 } 437 } 438 439 440 class VM_RevokeBias : public VM_Operation { 441 protected: 442 Handle* _obj; 443 GrowableArray<Handle>* _objs; 444 JavaThread* _requesting_thread; 445 BiasedLocking::Condition _status_code; 446 447 public: 448 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) 449 : _obj(obj) 450 , _objs(NULL) 451 , _requesting_thread(requesting_thread) 452 , _status_code(BiasedLocking::NOT_BIASED) {} 453 454 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) 455 : _obj(NULL) 456 , _objs(objs) 457 , _requesting_thread(requesting_thread) 458 , _status_code(BiasedLocking::NOT_BIASED) {} 459 460 virtual VMOp_Type type() const { return VMOp_RevokeBias; } 461 462 virtual bool doit_prologue() { 463 // Verify that there is actual work to do since the callers just 464 // give us locked object(s). If we don't find any biased objects 465 // there is nothing to do and we avoid a safepoint. 466 if (_obj != NULL) { 467 markOop mark = (*_obj)()->mark(); 468 if (mark->has_bias_pattern()) { 469 return true; 470 } 471 } else { 472 for ( int i = 0 ; i < _objs->length(); i++ ) { 473 markOop mark = (_objs->at(i))()->mark(); 474 if (mark->has_bias_pattern()) { 475 return true; 476 } 477 } 478 } 479 return false; 480 } 481 482 virtual void doit() { 483 if (_obj != NULL) { 484 if (TraceBiasedLocking) { 485 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); 486 } 487 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); 488 clean_up_cached_monitor_info(); 489 return; 490 } else { 491 if (TraceBiasedLocking) { 492 tty->print_cr("Revoking bias with global safepoint:"); 493 } 494 BiasedLocking::revoke_at_safepoint(_objs); 495 } 496 } 497 498 BiasedLocking::Condition status_code() const { 499 return _status_code; 500 } 501 }; 502 503 504 class VM_BulkRevokeBias : public VM_RevokeBias { 505 private: 506 bool _bulk_rebias; 507 bool _attempt_rebias_of_object; 508 509 public: 510 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 511 bool bulk_rebias, 512 bool attempt_rebias_of_object) 513 : VM_RevokeBias(obj, requesting_thread) 514 , _bulk_rebias(bulk_rebias) 515 , _attempt_rebias_of_object(attempt_rebias_of_object) {} 516 517 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 518 virtual bool doit_prologue() { return true; } 519 520 virtual void doit() { 521 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 522 clean_up_cached_monitor_info(); 523 } 524 }; 525 526 527 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 528 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 529 530 // We can revoke the biases of anonymously-biased objects 531 // efficiently enough that we should not cause these revocations to 532 // update the heuristics because doing so may cause unwanted bulk 533 // revocations (which are expensive) to occur. 534 markOop mark = obj->mark(); 535 if (mark->is_biased_anonymously() && !attempt_rebias) { 536 // We are probably trying to revoke the bias of this object due to 537 // an identity hash code computation. Try to revoke the bias 538 // without a safepoint. This is possible if we can successfully 539 // compare-and-exchange an unbiased header into the mark word of 540 // the object, meaning that no other thread has raced to acquire 541 // the bias of the object. 542 markOop biased_value = mark; 543 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 544 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 545 if (res_mark == biased_value) { 546 return BIAS_REVOKED; 547 } 548 } else if (mark->has_bias_pattern()) { 549 Klass* k = obj->klass(); 550 markOop prototype_header = k->prototype_header(); 551 if (!prototype_header->has_bias_pattern()) { 552 // This object has a stale bias from before the bulk revocation 553 // for this data type occurred. It's pointless to update the 554 // heuristics at this point so simply update the header with a 555 // CAS. If we fail this race, the object's bias has been revoked 556 // by another thread so we simply return and let the caller deal 557 // with it. 558 markOop biased_value = mark; 559 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); 560 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); 561 return BIAS_REVOKED; 562 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { 563 // The epoch of this biasing has expired indicating that the 564 // object is effectively unbiased. Depending on whether we need 565 // to rebias or revoke the bias of this object we can do it 566 // efficiently enough with a CAS that we shouldn't update the 567 // heuristics. This is normally done in the assembly code but we 568 // can reach this point due to various points in the runtime 569 // needing to revoke biases. 570 if (attempt_rebias) { 571 assert(THREAD->is_Java_thread(), ""); 572 markOop biased_value = mark; 573 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); 574 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); 575 if (res_mark == biased_value) { 576 return BIAS_REVOKED_AND_REBIASED; 577 } 578 } else { 579 markOop biased_value = mark; 580 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 581 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 582 if (res_mark == biased_value) { 583 return BIAS_REVOKED; 584 } 585 } 586 } 587 } 588 589 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); 590 if (heuristics == HR_NOT_BIASED) { 591 return NOT_BIASED; 592 } else if (heuristics == HR_SINGLE_REVOKE) { 593 Klass *k = obj->klass(); 594 markOop prototype_header = k->prototype_header(); 595 if (mark->biased_locker() == THREAD && 596 prototype_header->bias_epoch() == mark->bias_epoch()) { 597 // A thread is trying to revoke the bias of an object biased 598 // toward it, again likely due to an identity hash code 599 // computation. We can again avoid a safepoint in this case 600 // since we are only going to walk our own stack. There are no 601 // races with revocations occurring in other threads because we 602 // reach no safepoints in the revocation path. 603 // Also check the epoch because even if threads match, another thread 604 // can come in with a CAS to steal the bias of an object that has a 605 // stale epoch. 606 ResourceMark rm; 607 if (TraceBiasedLocking) { 608 tty->print_cr("Revoking bias by walking my own stack:"); 609 } 610 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); 611 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); 612 assert(cond == BIAS_REVOKED, "why not?"); 613 return cond; 614 } else { 615 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); 616 VMThread::execute(&revoke); 617 return revoke.status_code(); 618 } 619 } 620 621 assert((heuristics == HR_BULK_REVOKE) || 622 (heuristics == HR_BULK_REBIAS), "?"); 623 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, 624 (heuristics == HR_BULK_REBIAS), 625 attempt_rebias); 626 VMThread::execute(&bulk_revoke); 627 return bulk_revoke.status_code(); 628 } 629 630 631 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { 632 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 633 if (objs->length() == 0) { 634 return; 635 } 636 VM_RevokeBias revoke(objs, JavaThread::current()); 637 VMThread::execute(&revoke); 638 } 639 640 641 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 642 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 643 oop obj = h_obj(); 644 HeuristicsResult heuristics = update_heuristics(obj, false); 645 if (heuristics == HR_SINGLE_REVOKE) { 646 revoke_bias(obj, false, false, NULL); 647 } else if ((heuristics == HR_BULK_REBIAS) || 648 (heuristics == HR_BULK_REVOKE)) { 649 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 650 } 651 clean_up_cached_monitor_info(); 652 } 653 654 655 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 656 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 657 int len = objs->length(); 658 for (int i = 0; i < len; i++) { 659 oop obj = (objs->at(i))(); 660 HeuristicsResult heuristics = update_heuristics(obj, false); 661 if (heuristics == HR_SINGLE_REVOKE) { 662 revoke_bias(obj, false, false, NULL); 663 } else if ((heuristics == HR_BULK_REBIAS) || 664 (heuristics == HR_BULK_REVOKE)) { 665 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 666 } 667 } 668 clean_up_cached_monitor_info(); 669 } 670 671 672 void BiasedLocking::preserve_marks() { 673 if (!UseBiasedLocking) 674 return; 675 676 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 677 678 assert(_preserved_oop_stack == NULL, "double initialization"); 679 assert(_preserved_mark_stack == NULL, "double initialization"); 680 681 // In order to reduce the number of mark words preserved during GC 682 // due to the presence of biased locking, we reinitialize most mark 683 // words to the class's prototype during GC -- even those which have 684 // a currently valid bias owner. One important situation where we 685 // must not clobber a bias is when a biased object is currently 686 // locked. To handle this case we iterate over the currently-locked 687 // monitors in a prepass and, if they are biased, preserve their 688 // mark words here. This should be a relatively small set of objects 689 // especially compared to the number of objects in the heap. 690 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true); 691 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 692 693 ResourceMark rm; 694 Thread* cur = Thread::current(); 695 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { 696 if (thread->has_last_Java_frame()) { 697 RegisterMap rm(thread); 698 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 699 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 700 if (monitors != NULL) { 701 int len = monitors->length(); 702 // Walk monitors youngest to oldest 703 for (int i = len - 1; i >= 0; i--) { 704 MonitorInfo* mon_info = monitors->at(i); 705 if (mon_info->owner_is_scalar_replaced()) continue; 706 oop owner = mon_info->owner(); 707 if (owner != NULL) { 708 markOop mark = owner->mark(); 709 if (mark->has_bias_pattern()) { 710 _preserved_oop_stack->push(Handle(cur, owner)); 711 _preserved_mark_stack->push(mark); 712 } 713 } 714 } 715 } 716 } 717 } 718 } 719 } 720 721 722 void BiasedLocking::restore_marks() { 723 if (!UseBiasedLocking) 724 return; 725 726 assert(_preserved_oop_stack != NULL, "double free"); 727 assert(_preserved_mark_stack != NULL, "double free"); 728 729 int len = _preserved_oop_stack->length(); 730 for (int i = 0; i < len; i++) { 731 Handle owner = _preserved_oop_stack->at(i); 732 markOop mark = _preserved_mark_stack->at(i); 733 owner->set_mark(mark); 734 } 735 736 delete _preserved_oop_stack; 737 _preserved_oop_stack = NULL; 738 delete _preserved_mark_stack; 739 _preserved_mark_stack = NULL; 740 } 741 742 743 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 744 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 745 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 746 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 747 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 748 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 749 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 750 751 752 // BiasedLockingCounters 753 754 int BiasedLockingCounters::slow_path_entry_count() { 755 if (_slow_path_entry_count != 0) { 756 return _slow_path_entry_count; 757 } 758 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 759 _rebiased_lock_entry_count + _revoked_lock_entry_count + 760 _fast_path_entry_count; 761 762 return _total_entry_count - sum; 763 } 764 765 void BiasedLockingCounters::print_on(outputStream* st) { 766 tty->print_cr("# total entries: %d", _total_entry_count); 767 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 768 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 769 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 770 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 771 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 772 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 773 }