1 /* 2 * Copyright (c) 2005, 2014, 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/atomic.inline.hpp" 29 #include "runtime/basicLock.hpp" 30 #include "runtime/biasedLocking.hpp" 31 #include "runtime/task.hpp" 32 #include "runtime/vframe.hpp" 33 #include "runtime/vmThread.hpp" 34 #include "runtime/vm_operations.hpp" 35 36 static bool _biased_locking_enabled = false; 37 BiasedLockingCounters BiasedLocking::_counters; 38 39 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 40 static GrowableArray<markOop>* _preserved_mark_stack = NULL; 41 42 static void enable_biased_locking(Klass* k) { 43 k->set_prototype_header(markOopDesc::biased_locking_prototype()); 44 } 45 46 class VM_EnableBiasedLocking: public VM_Operation { 47 private: 48 bool _is_cheap_allocated; 49 public: 50 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } 51 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 52 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } 53 bool is_cheap_allocated() const { return _is_cheap_allocated; } 54 55 void doit() { 56 // Iterate the system dictionary enabling biased locking for all 57 // currently loaded classes 58 SystemDictionary::classes_do(enable_biased_locking); 59 // Indicate that future instances should enable it as well 60 _biased_locking_enabled = true; 61 62 if (TraceBiasedLocking) { 63 tty->print_cr("Biased locking enabled"); 64 } 65 } 66 67 bool allow_nested_vm_operations() const { return false; } 68 }; 69 70 71 // One-shot PeriodicTask subclass for enabling biased locking 72 class EnableBiasedLockingTask : public PeriodicTask { 73 public: 74 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 75 76 virtual void task() { 77 // Use async VM operation to avoid blocking the Watcher thread. 78 // VM Thread will free C heap storage. 79 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); 80 VMThread::execute(op); 81 82 // Reclaim our storage and disenroll ourself 83 delete this; 84 } 85 }; 86 87 88 void BiasedLocking::init() { 89 // If biased locking is enabled, schedule a task to fire a few 90 // seconds into the run which turns on biased locking for all 91 // currently loaded classes as well as future ones. This is a 92 // workaround for startup time regressions due to a large number of 93 // safepoints being taken during VM startup for bias revocation. 94 // Ideally we would have a lower cost for individual bias revocation 95 // and not need a mechanism like this. 96 if (UseBiasedLocking) { 97 if (BiasedLockingStartupDelay > 0) { 98 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 99 task->enroll(); 100 } else { 101 VM_EnableBiasedLocking op(false); 102 VMThread::execute(&op); 103 } 104 } 105 } 106 107 108 bool BiasedLocking::enabled() { 109 return _biased_locking_enabled; 110 } 111 112 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 113 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 114 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 115 if (info != NULL) { 116 return info; 117 } 118 119 info = new GrowableArray<MonitorInfo*>(); 120 121 // It's possible for the thread to not have any Java frames on it, 122 // i.e., if it's the main thread and it's already returned from main() 123 if (thread->has_last_Java_frame()) { 124 RegisterMap rm(thread); 125 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 126 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 127 if (monitors != NULL) { 128 int len = monitors->length(); 129 // Walk monitors youngest to oldest 130 for (int i = len - 1; i >= 0; i--) { 131 MonitorInfo* mon_info = monitors->at(i); 132 if (mon_info->eliminated()) continue; 133 oop owner = mon_info->owner(); 134 if (owner != NULL) { 135 info->append(mon_info); 136 } 137 } 138 } 139 } 140 } 141 142 thread->set_cached_monitor_info(info); 143 return info; 144 } 145 146 147 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { 148 markOop mark = obj->mark(); 149 if (!mark->has_bias_pattern()) { 150 if (TraceBiasedLocking) { 151 ResourceMark rm; 152 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", 153 obj->klass()->external_name()); 154 } 155 return BiasedLocking::NOT_BIASED; 156 } 157 158 uint age = mark->age(); 159 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); 160 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); 161 162 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 163 ResourceMark rm; 164 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, 165 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); 166 } 167 168 JavaThread* biased_thread = mark->biased_locker(); 169 if (biased_thread == NULL) { 170 // Object is anonymously biased. We can get here if, for 171 // example, we revoke the bias due to an identity hash code 172 // being computed for an object. 173 if (!allow_rebias) { 174 obj->set_mark(unbiased_prototype); 175 } 176 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 177 tty->print_cr(" Revoked bias of anonymously-biased object"); 178 } 179 return BiasedLocking::BIAS_REVOKED; 180 } 181 182 // Handle case where the thread toward which the object was biased has exited 183 bool thread_is_alive = false; 184 if (requesting_thread == biased_thread) { 185 thread_is_alive = true; 186 } else { 187 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { 188 if (cur_thread == biased_thread) { 189 thread_is_alive = true; 190 break; 191 } 192 } 193 } 194 if (!thread_is_alive) { 195 if (allow_rebias) { 196 obj->set_mark(biased_prototype); 197 } else { 198 obj->set_mark(unbiased_prototype); 199 } 200 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 201 tty->print_cr(" Revoked bias of object biased toward dead thread"); 202 } 203 return BiasedLocking::BIAS_REVOKED; 204 } 205 206 // Thread owning bias is alive. 207 // Check to see whether it currently owns the lock and, if so, 208 // write down the needed displaced headers to the thread's stack. 209 // Otherwise, restore the object's header either to the unlocked 210 // or unbiased state. 211 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 212 BasicLock* highest_lock = NULL; 213 for (int i = 0; i < cached_monitor_info->length(); i++) { 214 MonitorInfo* mon_info = cached_monitor_info->at(i); 215 if (mon_info->owner() == obj) { 216 if (TraceBiasedLocking && Verbose) { 217 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 218 p2i((void *) mon_info->owner()), 219 p2i((void *) obj)); 220 } 221 // Assume recursive case and fix up highest lock later 222 markOop mark = markOopDesc::encode((BasicLock*) NULL); 223 highest_lock = mon_info->lock(); 224 highest_lock->set_displaced_header(mark); 225 } else { 226 if (TraceBiasedLocking && Verbose) { 227 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 228 p2i((void *) mon_info->owner()), 229 p2i((void *) obj)); 230 } 231 } 232 } 233 if (highest_lock != NULL) { 234 // Fix up highest lock to contain displaced header and point 235 // object at it 236 highest_lock->set_displaced_header(unbiased_prototype); 237 // Reset object header to point to displaced mark. 238 // Must release storing the lock address for platforms without TSO 239 // ordering (e.g. ppc). 240 obj->release_set_mark(markOopDesc::encode(highest_lock)); 241 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 242 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 243 tty->print_cr(" Revoked bias of currently-locked object"); 244 } 245 } else { 246 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 247 tty->print_cr(" Revoked bias of currently-unlocked object"); 248 } 249 if (allow_rebias) { 250 obj->set_mark(biased_prototype); 251 } else { 252 // Store the unlocked value into the object's header. 253 obj->set_mark(unbiased_prototype); 254 } 255 } 256 257 return BiasedLocking::BIAS_REVOKED; 258 } 259 260 261 enum HeuristicsResult { 262 HR_NOT_BIASED = 1, 263 HR_SINGLE_REVOKE = 2, 264 HR_BULK_REBIAS = 3, 265 HR_BULK_REVOKE = 4 266 }; 267 268 269 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { 270 markOop mark = o->mark(); 271 if (!mark->has_bias_pattern()) { 272 return HR_NOT_BIASED; 273 } 274 275 // Heuristics to attempt to throttle the number of revocations. 276 // Stages: 277 // 1. Revoke the biases of all objects in the heap of this type, 278 // but allow rebiasing of those objects if unlocked. 279 // 2. Revoke the biases of all objects in the heap of this type 280 // and don't allow rebiasing of these objects. Disable 281 // allocation of objects of that type with the bias bit set. 282 Klass* k = o->klass(); 283 jlong cur_time = os::javaTimeMillis(); 284 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 285 int revocation_count = k->biased_lock_revocation_count(); 286 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 287 (revocation_count < BiasedLockingBulkRevokeThreshold) && 288 (last_bulk_revocation_time != 0) && 289 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 290 // This is the first revocation we've seen in a while of an 291 // object of this type since the last time we performed a bulk 292 // rebiasing operation. The application is allocating objects in 293 // bulk which are biased toward a thread and then handing them 294 // off to another thread. We can cope with this allocation 295 // pattern via the bulk rebiasing mechanism so we reset the 296 // klass's revocation count rather than allow it to increase 297 // monotonically. If we see the need to perform another bulk 298 // rebias operation later, we will, and if subsequently we see 299 // many more revocation operations in a short period of time we 300 // will completely disable biasing for this type. 301 k->set_biased_lock_revocation_count(0); 302 revocation_count = 0; 303 } 304 305 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 306 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 307 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 308 } 309 310 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 311 return HR_BULK_REVOKE; 312 } 313 314 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 315 return HR_BULK_REBIAS; 316 } 317 318 return HR_SINGLE_REVOKE; 319 } 320 321 322 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, 323 bool bulk_rebias, 324 bool attempt_rebias_of_object, 325 JavaThread* requesting_thread) { 326 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 327 328 if (TraceBiasedLocking) { 329 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " 330 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 331 (bulk_rebias ? "rebias" : "revoke"), 332 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name()); 333 } 334 335 jlong cur_time = os::javaTimeMillis(); 336 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 337 338 339 Klass* k_o = o->klass(); 340 Klass* klass = k_o; 341 342 if (bulk_rebias) { 343 // Use the epoch in the klass of the object to implicitly revoke 344 // all biases of objects of this data type and force them to be 345 // reacquired. However, we also need to walk the stacks of all 346 // threads and update the headers of lightweight locked objects 347 // with biases to have the current epoch. 348 349 // If the prototype header doesn't have the bias pattern, don't 350 // try to update the epoch -- assume another VM operation came in 351 // and reset the header to the unbiased state, which will 352 // implicitly cause all existing biases to be revoked 353 if (klass->prototype_header()->has_bias_pattern()) { 354 int prev_epoch = klass->prototype_header()->bias_epoch(); 355 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); 356 int cur_epoch = klass->prototype_header()->bias_epoch(); 357 358 // Now walk all threads' stacks and adjust epochs of any biased 359 // and locked objects of this data type we encounter 360 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 361 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 362 for (int i = 0; i < cached_monitor_info->length(); i++) { 363 MonitorInfo* mon_info = cached_monitor_info->at(i); 364 oop owner = mon_info->owner(); 365 markOop mark = owner->mark(); 366 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 367 // We might have encountered this object already in the case of recursive locking 368 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 369 owner->set_mark(mark->set_bias_epoch(cur_epoch)); 370 } 371 } 372 } 373 } 374 375 // At this point we're done. All we have to do is potentially 376 // adjust the header of the given object to revoke its bias. 377 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); 378 } else { 379 if (TraceBiasedLocking) { 380 ResourceMark rm; 381 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); 382 } 383 384 // Disable biased locking for this data type. Not only will this 385 // cause future instances to not be biased, but existing biased 386 // instances will notice that this implicitly caused their biases 387 // to be revoked. 388 klass->set_prototype_header(markOopDesc::prototype()); 389 390 // Now walk all threads' stacks and forcibly revoke the biases of 391 // any locked and biased objects of this data type we encounter. 392 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 393 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 394 for (int i = 0; i < cached_monitor_info->length(); i++) { 395 MonitorInfo* mon_info = cached_monitor_info->at(i); 396 oop owner = mon_info->owner(); 397 markOop mark = owner->mark(); 398 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 399 revoke_bias(owner, false, true, requesting_thread); 400 } 401 } 402 } 403 404 // Must force the bias of the passed object to be forcibly revoked 405 // as well to ensure guarantees to callers 406 revoke_bias(o, false, true, requesting_thread); 407 } 408 409 if (TraceBiasedLocking) { 410 tty->print_cr("* Ending bulk revocation"); 411 } 412 413 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; 414 415 if (attempt_rebias_of_object && 416 o->mark()->has_bias_pattern() && 417 klass->prototype_header()->has_bias_pattern()) { 418 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), 419 klass->prototype_header()->bias_epoch()); 420 o->set_mark(new_mark); 421 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; 422 if (TraceBiasedLocking) { 423 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 424 } 425 } 426 427 assert(!o->mark()->has_bias_pattern() || 428 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), 429 "bug in bulk bias revocation"); 430 431 return status_code; 432 } 433 434 435 static void clean_up_cached_monitor_info() { 436 // Walk the thread list clearing out the cached monitors 437 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 438 thr->set_cached_monitor_info(NULL); 439 } 440 } 441 442 443 class VM_RevokeBias : public VM_Operation { 444 protected: 445 Handle* _obj; 446 GrowableArray<Handle>* _objs; 447 JavaThread* _requesting_thread; 448 BiasedLocking::Condition _status_code; 449 450 public: 451 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) 452 : _obj(obj) 453 , _objs(NULL) 454 , _requesting_thread(requesting_thread) 455 , _status_code(BiasedLocking::NOT_BIASED) {} 456 457 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) 458 : _obj(NULL) 459 , _objs(objs) 460 , _requesting_thread(requesting_thread) 461 , _status_code(BiasedLocking::NOT_BIASED) {} 462 463 virtual VMOp_Type type() const { return VMOp_RevokeBias; } 464 465 virtual bool doit_prologue() { 466 // Verify that there is actual work to do since the callers just 467 // give us locked object(s). If we don't find any biased objects 468 // there is nothing to do and we avoid a safepoint. 469 if (_obj != NULL) { 470 markOop mark = (*_obj)()->mark(); 471 if (mark->has_bias_pattern()) { 472 return true; 473 } 474 } else { 475 for ( int i = 0 ; i < _objs->length(); i++ ) { 476 markOop mark = (_objs->at(i))()->mark(); 477 if (mark->has_bias_pattern()) { 478 return true; 479 } 480 } 481 } 482 return false; 483 } 484 485 virtual void doit() { 486 if (_obj != NULL) { 487 if (TraceBiasedLocking) { 488 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); 489 } 490 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); 491 clean_up_cached_monitor_info(); 492 return; 493 } else { 494 if (TraceBiasedLocking) { 495 tty->print_cr("Revoking bias with global safepoint:"); 496 } 497 BiasedLocking::revoke_at_safepoint(_objs); 498 } 499 } 500 501 BiasedLocking::Condition status_code() const { 502 return _status_code; 503 } 504 }; 505 506 507 class VM_BulkRevokeBias : public VM_RevokeBias { 508 private: 509 bool _bulk_rebias; 510 bool _attempt_rebias_of_object; 511 512 public: 513 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 514 bool bulk_rebias, 515 bool attempt_rebias_of_object) 516 : VM_RevokeBias(obj, requesting_thread) 517 , _bulk_rebias(bulk_rebias) 518 , _attempt_rebias_of_object(attempt_rebias_of_object) {} 519 520 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 521 virtual bool doit_prologue() { return true; } 522 523 virtual void doit() { 524 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 525 clean_up_cached_monitor_info(); 526 } 527 }; 528 529 530 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 531 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 532 533 // We can revoke the biases of anonymously-biased objects 534 // efficiently enough that we should not cause these revocations to 535 // update the heuristics because doing so may cause unwanted bulk 536 // revocations (which are expensive) to occur. 537 markOop mark = obj->mark(); 538 if (mark->is_biased_anonymously() && !attempt_rebias) { 539 // We are probably trying to revoke the bias of this object due to 540 // an identity hash code computation. Try to revoke the bias 541 // without a safepoint. This is possible if we can successfully 542 // compare-and-exchange an unbiased header into the mark word of 543 // the object, meaning that no other thread has raced to acquire 544 // the bias of the object. 545 markOop biased_value = mark; 546 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 547 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 548 if (res_mark == biased_value) { 549 return BIAS_REVOKED; 550 } 551 } else if (mark->has_bias_pattern()) { 552 Klass* k = obj->klass(); 553 markOop prototype_header = k->prototype_header(); 554 if (!prototype_header->has_bias_pattern()) { 555 // This object has a stale bias from before the bulk revocation 556 // for this data type occurred. It's pointless to update the 557 // heuristics at this point so simply update the header with a 558 // CAS. If we fail this race, the object's bias has been revoked 559 // by another thread so we simply return and let the caller deal 560 // with it. 561 markOop biased_value = mark; 562 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); 563 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); 564 return BIAS_REVOKED; 565 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { 566 // The epoch of this biasing has expired indicating that the 567 // object is effectively unbiased. Depending on whether we need 568 // to rebias or revoke the bias of this object we can do it 569 // efficiently enough with a CAS that we shouldn't update the 570 // heuristics. This is normally done in the assembly code but we 571 // can reach this point due to various points in the runtime 572 // needing to revoke biases. 573 if (attempt_rebias) { 574 assert(THREAD->is_Java_thread(), ""); 575 markOop biased_value = mark; 576 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); 577 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); 578 if (res_mark == biased_value) { 579 return BIAS_REVOKED_AND_REBIASED; 580 } 581 } else { 582 markOop biased_value = mark; 583 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 584 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 585 if (res_mark == biased_value) { 586 return BIAS_REVOKED; 587 } 588 } 589 } 590 } 591 592 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); 593 if (heuristics == HR_NOT_BIASED) { 594 return NOT_BIASED; 595 } else if (heuristics == HR_SINGLE_REVOKE) { 596 Klass *k = obj->klass(); 597 markOop prototype_header = k->prototype_header(); 598 if (mark->biased_locker() == THREAD && 599 prototype_header->bias_epoch() == mark->bias_epoch()) { 600 // A thread is trying to revoke the bias of an object biased 601 // toward it, again likely due to an identity hash code 602 // computation. We can again avoid a safepoint in this case 603 // since we are only going to walk our own stack. There are no 604 // races with revocations occurring in other threads because we 605 // reach no safepoints in the revocation path. 606 // Also check the epoch because even if threads match, another thread 607 // can come in with a CAS to steal the bias of an object that has a 608 // stale epoch. 609 ResourceMark rm; 610 if (TraceBiasedLocking) { 611 tty->print_cr("Revoking bias by walking my own stack:"); 612 } 613 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); 614 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); 615 assert(cond == BIAS_REVOKED, "why not?"); 616 return cond; 617 } else { 618 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); 619 VMThread::execute(&revoke); 620 return revoke.status_code(); 621 } 622 } 623 624 assert((heuristics == HR_BULK_REVOKE) || 625 (heuristics == HR_BULK_REBIAS), "?"); 626 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, 627 (heuristics == HR_BULK_REBIAS), 628 attempt_rebias); 629 VMThread::execute(&bulk_revoke); 630 return bulk_revoke.status_code(); 631 } 632 633 634 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { 635 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 636 if (objs->length() == 0) { 637 return; 638 } 639 VM_RevokeBias revoke(objs, JavaThread::current()); 640 VMThread::execute(&revoke); 641 } 642 643 644 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 645 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 646 oop obj = h_obj(); 647 HeuristicsResult heuristics = update_heuristics(obj, false); 648 if (heuristics == HR_SINGLE_REVOKE) { 649 revoke_bias(obj, false, false, NULL); 650 } else if ((heuristics == HR_BULK_REBIAS) || 651 (heuristics == HR_BULK_REVOKE)) { 652 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 653 } 654 clean_up_cached_monitor_info(); 655 } 656 657 658 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 659 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 660 int len = objs->length(); 661 for (int i = 0; i < len; i++) { 662 oop obj = (objs->at(i))(); 663 HeuristicsResult heuristics = update_heuristics(obj, false); 664 if (heuristics == HR_SINGLE_REVOKE) { 665 revoke_bias(obj, false, false, NULL); 666 } else if ((heuristics == HR_BULK_REBIAS) || 667 (heuristics == HR_BULK_REVOKE)) { 668 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 669 } 670 } 671 clean_up_cached_monitor_info(); 672 } 673 674 675 void BiasedLocking::preserve_marks() { 676 if (!UseBiasedLocking) 677 return; 678 679 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 680 681 assert(_preserved_oop_stack == NULL, "double initialization"); 682 assert(_preserved_mark_stack == NULL, "double initialization"); 683 684 // In order to reduce the number of mark words preserved during GC 685 // due to the presence of biased locking, we reinitialize most mark 686 // words to the class's prototype during GC -- even those which have 687 // a currently valid bias owner. One important situation where we 688 // must not clobber a bias is when a biased object is currently 689 // locked. To handle this case we iterate over the currently-locked 690 // monitors in a prepass and, if they are biased, preserve their 691 // mark words here. This should be a relatively small set of objects 692 // especially compared to the number of objects in the heap. 693 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true); 694 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 695 696 ResourceMark rm; 697 Thread* cur = Thread::current(); 698 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { 699 if (thread->has_last_Java_frame()) { 700 RegisterMap rm(thread); 701 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 702 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 703 if (monitors != NULL) { 704 int len = monitors->length(); 705 // Walk monitors youngest to oldest 706 for (int i = len - 1; i >= 0; i--) { 707 MonitorInfo* mon_info = monitors->at(i); 708 if (mon_info->owner_is_scalar_replaced()) continue; 709 oop owner = mon_info->owner(); 710 if (owner != NULL) { 711 markOop mark = owner->mark(); 712 if (mark->has_bias_pattern()) { 713 _preserved_oop_stack->push(Handle(cur, owner)); 714 _preserved_mark_stack->push(mark); 715 } 716 } 717 } 718 } 719 } 720 } 721 } 722 } 723 724 725 void BiasedLocking::restore_marks() { 726 if (!UseBiasedLocking) 727 return; 728 729 assert(_preserved_oop_stack != NULL, "double free"); 730 assert(_preserved_mark_stack != NULL, "double free"); 731 732 int len = _preserved_oop_stack->length(); 733 for (int i = 0; i < len; i++) { 734 Handle owner = _preserved_oop_stack->at(i); 735 markOop mark = _preserved_mark_stack->at(i); 736 owner->set_mark(mark); 737 } 738 739 delete _preserved_oop_stack; 740 _preserved_oop_stack = NULL; 741 delete _preserved_mark_stack; 742 _preserved_mark_stack = NULL; 743 } 744 745 746 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 747 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 748 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 749 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 750 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 751 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 752 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 753 754 755 // BiasedLockingCounters 756 757 int BiasedLockingCounters::slow_path_entry_count() { 758 if (_slow_path_entry_count != 0) { 759 return _slow_path_entry_count; 760 } 761 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 762 _rebiased_lock_entry_count + _revoked_lock_entry_count + 763 _fast_path_entry_count; 764 765 return _total_entry_count - sum; 766 } 767 768 void BiasedLockingCounters::print_on(outputStream* st) { 769 tty->print_cr("# total entries: %d", _total_entry_count); 770 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 771 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 772 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 773 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 774 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 775 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 776 }