1 /* 2 * Copyright (c) 2005, 2015, 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 "oops/oop.inline.hpp" 29 #include "runtime/atomic.inline.hpp" 30 #include "runtime/basicLock.hpp" 31 #include "runtime/biasedLocking.hpp" 32 #include "runtime/task.hpp" 33 #include "runtime/vframe.hpp" 34 #include "runtime/vmThread.hpp" 35 #include "runtime/vm_operations.hpp" 36 37 static bool _biased_locking_enabled = false; 38 BiasedLockingCounters BiasedLocking::_counters; 39 40 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 41 static GrowableArray<markOop>* _preserved_mark_stack = NULL; 42 43 static void enable_biased_locking(Klass* k) { 44 k->set_prototype_header(markOopDesc::biased_locking_prototype()); 45 } 46 47 class VM_EnableBiasedLocking: public VM_Operation { 48 private: 49 bool _is_cheap_allocated; 50 public: 51 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } 52 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 53 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } 54 bool is_cheap_allocated() const { return _is_cheap_allocated; } 55 56 void doit() { 57 // Iterate the system dictionary enabling biased locking for all 58 // currently loaded classes 59 SystemDictionary::classes_do(enable_biased_locking); 60 // Indicate that future instances should enable it as well 61 _biased_locking_enabled = true; 62 63 if (TraceBiasedLocking) { 64 tty->print_cr("Biased locking enabled"); 65 } 66 } 67 68 bool allow_nested_vm_operations() const { return false; } 69 }; 70 71 72 // One-shot PeriodicTask subclass for enabling biased locking 73 class EnableBiasedLockingTask : public PeriodicTask { 74 public: 75 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 76 77 virtual void task() { 78 // Use async VM operation to avoid blocking the Watcher thread. 79 // VM Thread will free C heap storage. 80 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); 81 VMThread::execute(op); 82 83 // Reclaim our storage and disenroll ourself 84 delete this; 85 } 86 }; 87 88 89 void BiasedLocking::init() { 90 // If biased locking is enabled, schedule a task to fire a few 91 // seconds into the run which turns on biased locking for all 92 // currently loaded classes as well as future ones. This is a 93 // workaround for startup time regressions due to a large number of 94 // safepoints being taken during VM startup for bias revocation. 95 // Ideally we would have a lower cost for individual bias revocation 96 // and not need a mechanism like this. 97 if (UseBiasedLocking) { 98 if (BiasedLockingStartupDelay > 0) { 99 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 100 task->enroll(); 101 } else { 102 VM_EnableBiasedLocking op(false); 103 VMThread::execute(&op); 104 } 105 } 106 } 107 108 109 bool BiasedLocking::enabled() { 110 return _biased_locking_enabled; 111 } 112 113 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 114 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 115 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 116 if (info != NULL) { 117 return info; 118 } 119 120 info = new GrowableArray<MonitorInfo*>(); 121 122 // It's possible for the thread to not have any Java frames on it, 123 // i.e., if it's the main thread and it's already returned from main() 124 if (thread->has_last_Java_frame()) { 125 RegisterMap rm(thread); 126 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 127 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 128 if (monitors != NULL) { 129 int len = monitors->length(); 130 // Walk monitors youngest to oldest 131 for (int i = len - 1; i >= 0; i--) { 132 MonitorInfo* mon_info = monitors->at(i); 133 if (mon_info->eliminated()) continue; 134 oop owner = mon_info->owner(); 135 if (owner != NULL) { 136 info->append(mon_info); 137 } 138 } 139 } 140 } 141 } 142 143 thread->set_cached_monitor_info(info); 144 return info; 145 } 146 147 148 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { 149 assert(obj == oopDesc::bs()->read_barrier(obj), "expect to-space copy"); 150 markOop mark = obj->mark(); 151 if (!mark->has_bias_pattern()) { 152 if (TraceBiasedLocking) { 153 ResourceMark rm; 154 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", 155 obj->klass()->external_name()); 156 } 157 return BiasedLocking::NOT_BIASED; 158 } 159 160 uint age = mark->age(); 161 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); 162 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); 163 164 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 165 ResourceMark rm; 166 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, 167 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); 168 } 169 170 JavaThread* biased_thread = mark->biased_locker(); 171 if (biased_thread == NULL) { 172 // Object is anonymously biased. We can get here if, for 173 // example, we revoke the bias due to an identity hash code 174 // being computed for an object. 175 if (!allow_rebias) { 176 obj->set_mark(unbiased_prototype); 177 } 178 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 179 tty->print_cr(" Revoked bias of anonymously-biased object"); 180 } 181 return BiasedLocking::BIAS_REVOKED; 182 } 183 184 // Handle case where the thread toward which the object was biased has exited 185 bool thread_is_alive = false; 186 if (requesting_thread == biased_thread) { 187 thread_is_alive = true; 188 } else { 189 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { 190 if (cur_thread == biased_thread) { 191 thread_is_alive = true; 192 break; 193 } 194 } 195 } 196 if (!thread_is_alive) { 197 if (allow_rebias) { 198 obj->set_mark(biased_prototype); 199 } else { 200 obj->set_mark(unbiased_prototype); 201 } 202 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 203 tty->print_cr(" Revoked bias of object biased toward dead thread"); 204 } 205 return BiasedLocking::BIAS_REVOKED; 206 } 207 208 // Thread owning bias is alive. 209 // Check to see whether it currently owns the lock and, if so, 210 // write down the needed displaced headers to the thread's stack. 211 // Otherwise, restore the object's header either to the unlocked 212 // or unbiased state. 213 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 214 BasicLock* highest_lock = NULL; 215 for (int i = 0; i < cached_monitor_info->length(); i++) { 216 MonitorInfo* mon_info = cached_monitor_info->at(i); 217 if (mon_info->owner() == obj) { 218 if (TraceBiasedLocking && Verbose) { 219 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 220 p2i((void *) mon_info->owner()), 221 p2i((void *) obj)); 222 } 223 // Assume recursive case and fix up highest lock later 224 markOop mark = markOopDesc::encode((BasicLock*) NULL); 225 highest_lock = mon_info->lock(); 226 highest_lock->set_displaced_header(mark); 227 } else { 228 if (TraceBiasedLocking && Verbose) { 229 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 230 p2i((void *) mon_info->owner()), 231 p2i((void *) obj)); 232 } 233 } 234 } 235 if (highest_lock != NULL) { 236 // Fix up highest lock to contain displaced header and point 237 // object at it 238 highest_lock->set_displaced_header(unbiased_prototype); 239 // Reset object header to point to displaced mark. 240 // Must release storing the lock address for platforms without TSO 241 // ordering (e.g. ppc). 242 obj->release_set_mark(markOopDesc::encode(highest_lock)); 243 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 244 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 245 tty->print_cr(" Revoked bias of currently-locked object"); 246 } 247 } else { 248 if (TraceBiasedLocking && (Verbose || !is_bulk)) { 249 tty->print_cr(" Revoked bias of currently-unlocked object"); 250 } 251 if (allow_rebias) { 252 obj->set_mark(biased_prototype); 253 } else { 254 // Store the unlocked value into the object's header. 255 obj->set_mark(unbiased_prototype); 256 } 257 } 258 259 return BiasedLocking::BIAS_REVOKED; 260 } 261 262 263 enum HeuristicsResult { 264 HR_NOT_BIASED = 1, 265 HR_SINGLE_REVOKE = 2, 266 HR_BULK_REBIAS = 3, 267 HR_BULK_REVOKE = 4 268 }; 269 270 271 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { 272 markOop mark = o->mark(); 273 if (!mark->has_bias_pattern()) { 274 return HR_NOT_BIASED; 275 } 276 277 // Heuristics to attempt to throttle the number of revocations. 278 // Stages: 279 // 1. Revoke the biases of all objects in the heap of this type, 280 // but allow rebiasing of those objects if unlocked. 281 // 2. Revoke the biases of all objects in the heap of this type 282 // and don't allow rebiasing of these objects. Disable 283 // allocation of objects of that type with the bias bit set. 284 Klass* k = o->klass(); 285 jlong cur_time = os::javaTimeMillis(); 286 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 287 int revocation_count = k->biased_lock_revocation_count(); 288 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 289 (revocation_count < BiasedLockingBulkRevokeThreshold) && 290 (last_bulk_revocation_time != 0) && 291 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 292 // This is the first revocation we've seen in a while of an 293 // object of this type since the last time we performed a bulk 294 // rebiasing operation. The application is allocating objects in 295 // bulk which are biased toward a thread and then handing them 296 // off to another thread. We can cope with this allocation 297 // pattern via the bulk rebiasing mechanism so we reset the 298 // klass's revocation count rather than allow it to increase 299 // monotonically. If we see the need to perform another bulk 300 // rebias operation later, we will, and if subsequently we see 301 // many more revocation operations in a short period of time we 302 // will completely disable biasing for this type. 303 k->set_biased_lock_revocation_count(0); 304 revocation_count = 0; 305 } 306 307 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 308 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 309 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 310 } 311 312 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 313 return HR_BULK_REVOKE; 314 } 315 316 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 317 return HR_BULK_REBIAS; 318 } 319 320 return HR_SINGLE_REVOKE; 321 } 322 323 324 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, 325 bool bulk_rebias, 326 bool attempt_rebias_of_object, 327 JavaThread* requesting_thread) { 328 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 329 assert(o == oopDesc::bs()->read_barrier(o), "expect to-space copy"); 330 if (TraceBiasedLocking) { 331 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " 332 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 333 (bulk_rebias ? "rebias" : "revoke"), 334 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name()); 335 } 336 337 jlong cur_time = os::javaTimeMillis(); 338 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 339 340 341 Klass* k_o = o->klass(); 342 Klass* klass = k_o; 343 344 if (bulk_rebias) { 345 // Use the epoch in the klass of the object to implicitly revoke 346 // all biases of objects of this data type and force them to be 347 // reacquired. However, we also need to walk the stacks of all 348 // threads and update the headers of lightweight locked objects 349 // with biases to have the current epoch. 350 351 // If the prototype header doesn't have the bias pattern, don't 352 // try to update the epoch -- assume another VM operation came in 353 // and reset the header to the unbiased state, which will 354 // implicitly cause all existing biases to be revoked 355 if (klass->prototype_header()->has_bias_pattern()) { 356 int prev_epoch = klass->prototype_header()->bias_epoch(); 357 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); 358 int cur_epoch = klass->prototype_header()->bias_epoch(); 359 360 // Now walk all threads' stacks and adjust epochs of any biased 361 // and locked objects of this data type we encounter 362 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 363 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 364 for (int i = 0; i < cached_monitor_info->length(); i++) { 365 MonitorInfo* mon_info = cached_monitor_info->at(i); 366 oop owner = mon_info->owner(); 367 markOop mark = owner->mark(); 368 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 369 // We might have encountered this object already in the case of recursive locking 370 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 371 assert(owner == oopDesc::bs()->read_barrier(owner), "expect to-space copy"); 372 owner->set_mark(mark->set_bias_epoch(cur_epoch)); 373 } 374 } 375 } 376 } 377 378 // At this point we're done. All we have to do is potentially 379 // adjust the header of the given object to revoke its bias. 380 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); 381 } else { 382 if (TraceBiasedLocking) { 383 ResourceMark rm; 384 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); 385 } 386 387 // Disable biased locking for this data type. Not only will this 388 // cause future instances to not be biased, but existing biased 389 // instances will notice that this implicitly caused their biases 390 // to be revoked. 391 klass->set_prototype_header(markOopDesc::prototype()); 392 393 // Now walk all threads' stacks and forcibly revoke the biases of 394 // any locked and biased objects of this data type we encounter. 395 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 396 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 397 for (int i = 0; i < cached_monitor_info->length(); i++) { 398 MonitorInfo* mon_info = cached_monitor_info->at(i); 399 oop owner = mon_info->owner(); 400 markOop mark = owner->mark(); 401 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 402 revoke_bias(owner, false, true, requesting_thread); 403 } 404 } 405 } 406 407 // Must force the bias of the passed object to be forcibly revoked 408 // as well to ensure guarantees to callers 409 revoke_bias(o, false, true, requesting_thread); 410 } 411 412 if (TraceBiasedLocking) { 413 tty->print_cr("* Ending bulk revocation"); 414 } 415 416 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; 417 418 if (attempt_rebias_of_object && 419 o->mark()->has_bias_pattern() && 420 klass->prototype_header()->has_bias_pattern()) { 421 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), 422 klass->prototype_header()->bias_epoch()); 423 o->set_mark(new_mark); 424 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; 425 if (TraceBiasedLocking) { 426 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 427 } 428 } 429 430 assert(!o->mark()->has_bias_pattern() || 431 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), 432 "bug in bulk bias revocation"); 433 434 return status_code; 435 } 436 437 438 static void clean_up_cached_monitor_info() { 439 // Walk the thread list clearing out the cached monitors 440 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 441 thr->set_cached_monitor_info(NULL); 442 } 443 } 444 445 446 class VM_RevokeBias : public VM_Operation { 447 protected: 448 Handle* _obj; 449 GrowableArray<Handle>* _objs; 450 JavaThread* _requesting_thread; 451 BiasedLocking::Condition _status_code; 452 453 public: 454 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) 455 : _obj(obj) 456 , _objs(NULL) 457 , _requesting_thread(requesting_thread) 458 , _status_code(BiasedLocking::NOT_BIASED) {} 459 460 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) 461 : _obj(NULL) 462 , _objs(objs) 463 , _requesting_thread(requesting_thread) 464 , _status_code(BiasedLocking::NOT_BIASED) {} 465 466 virtual VMOp_Type type() const { return VMOp_RevokeBias; } 467 468 virtual bool doit_prologue() { 469 // Verify that there is actual work to do since the callers just 470 // give us locked object(s). If we don't find any biased objects 471 // there is nothing to do and we avoid a safepoint. 472 if (_obj != NULL) { 473 markOop mark = (*_obj)()->mark(); 474 if (mark->has_bias_pattern()) { 475 return true; 476 } 477 } else { 478 for ( int i = 0 ; i < _objs->length(); i++ ) { 479 markOop mark = (_objs->at(i))()->mark(); 480 if (mark->has_bias_pattern()) { 481 return true; 482 } 483 } 484 } 485 return false; 486 } 487 488 virtual void doit() { 489 if (_obj != NULL) { 490 if (TraceBiasedLocking) { 491 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); 492 } 493 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); 494 clean_up_cached_monitor_info(); 495 return; 496 } else { 497 if (TraceBiasedLocking) { 498 tty->print_cr("Revoking bias with global safepoint:"); 499 } 500 BiasedLocking::revoke_at_safepoint(_objs); 501 } 502 } 503 504 BiasedLocking::Condition status_code() const { 505 return _status_code; 506 } 507 }; 508 509 510 class VM_BulkRevokeBias : public VM_RevokeBias { 511 private: 512 bool _bulk_rebias; 513 bool _attempt_rebias_of_object; 514 515 public: 516 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 517 bool bulk_rebias, 518 bool attempt_rebias_of_object) 519 : VM_RevokeBias(obj, requesting_thread) 520 , _bulk_rebias(bulk_rebias) 521 , _attempt_rebias_of_object(attempt_rebias_of_object) {} 522 523 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 524 virtual bool doit_prologue() { return true; } 525 526 virtual void doit() { 527 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 528 clean_up_cached_monitor_info(); 529 } 530 }; 531 532 533 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 534 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 535 536 assert(obj() == oopDesc::bs()->read_barrier(obj()), "must be to-space copy"); 537 538 // We can revoke the biases of anonymously-biased objects 539 // efficiently enough that we should not cause these revocations to 540 // update the heuristics because doing so may cause unwanted bulk 541 // revocations (which are expensive) to occur. 542 markOop mark = obj->mark(); 543 if (mark->is_biased_anonymously() && !attempt_rebias) { 544 // We are probably trying to revoke the bias of this object due to 545 // an identity hash code computation. Try to revoke the bias 546 // without a safepoint. This is possible if we can successfully 547 // compare-and-exchange an unbiased header into the mark word of 548 // the object, meaning that no other thread has raced to acquire 549 // the bias of the object. 550 markOop biased_value = mark; 551 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 552 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 553 if (res_mark == biased_value) { 554 return BIAS_REVOKED; 555 } 556 } else if (mark->has_bias_pattern()) { 557 Klass* k = obj->klass(); 558 markOop prototype_header = k->prototype_header(); 559 if (!prototype_header->has_bias_pattern()) { 560 // This object has a stale bias from before the bulk revocation 561 // for this data type occurred. It's pointless to update the 562 // heuristics at this point so simply update the header with a 563 // CAS. If we fail this race, the object's bias has been revoked 564 // by another thread so we simply return and let the caller deal 565 // with it. 566 markOop biased_value = mark; 567 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); 568 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); 569 return BIAS_REVOKED; 570 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { 571 // The epoch of this biasing has expired indicating that the 572 // object is effectively unbiased. Depending on whether we need 573 // to rebias or revoke the bias of this object we can do it 574 // efficiently enough with a CAS that we shouldn't update the 575 // heuristics. This is normally done in the assembly code but we 576 // can reach this point due to various points in the runtime 577 // needing to revoke biases. 578 if (attempt_rebias) { 579 assert(THREAD->is_Java_thread(), ""); 580 markOop biased_value = mark; 581 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); 582 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); 583 if (res_mark == biased_value) { 584 return BIAS_REVOKED_AND_REBIASED; 585 } 586 } else { 587 markOop biased_value = mark; 588 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 589 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 590 if (res_mark == biased_value) { 591 return BIAS_REVOKED; 592 } 593 } 594 } 595 } 596 597 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); 598 if (heuristics == HR_NOT_BIASED) { 599 return NOT_BIASED; 600 } else if (heuristics == HR_SINGLE_REVOKE) { 601 Klass *k = obj->klass(); 602 markOop prototype_header = k->prototype_header(); 603 if (mark->biased_locker() == THREAD && 604 prototype_header->bias_epoch() == mark->bias_epoch()) { 605 // A thread is trying to revoke the bias of an object biased 606 // toward it, again likely due to an identity hash code 607 // computation. We can again avoid a safepoint in this case 608 // since we are only going to walk our own stack. There are no 609 // races with revocations occurring in other threads because we 610 // reach no safepoints in the revocation path. 611 // Also check the epoch because even if threads match, another thread 612 // can come in with a CAS to steal the bias of an object that has a 613 // stale epoch. 614 ResourceMark rm; 615 if (TraceBiasedLocking) { 616 tty->print_cr("Revoking bias by walking my own stack:"); 617 } 618 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); 619 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); 620 assert(cond == BIAS_REVOKED, "why not?"); 621 return cond; 622 } else { 623 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); 624 VMThread::execute(&revoke); 625 return revoke.status_code(); 626 } 627 } 628 629 assert((heuristics == HR_BULK_REVOKE) || 630 (heuristics == HR_BULK_REBIAS), "?"); 631 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, 632 (heuristics == HR_BULK_REBIAS), 633 attempt_rebias); 634 VMThread::execute(&bulk_revoke); 635 return bulk_revoke.status_code(); 636 } 637 638 639 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { 640 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 641 if (objs->length() == 0) { 642 return; 643 } 644 VM_RevokeBias revoke(objs, JavaThread::current()); 645 VMThread::execute(&revoke); 646 } 647 648 649 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 650 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 651 oop obj = h_obj(); 652 assert(obj == oopDesc::bs()->read_barrier(obj), "expect to-space copy"); 653 HeuristicsResult heuristics = update_heuristics(obj, false); 654 if (heuristics == HR_SINGLE_REVOKE) { 655 revoke_bias(obj, false, false, NULL); 656 } else if ((heuristics == HR_BULK_REBIAS) || 657 (heuristics == HR_BULK_REVOKE)) { 658 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 659 } 660 clean_up_cached_monitor_info(); 661 } 662 663 664 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 665 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 666 int len = objs->length(); 667 for (int i = 0; i < len; i++) { 668 oop obj = (objs->at(i))(); 669 HeuristicsResult heuristics = update_heuristics(obj, false); 670 if (heuristics == HR_SINGLE_REVOKE) { 671 revoke_bias(obj, false, false, NULL); 672 } else if ((heuristics == HR_BULK_REBIAS) || 673 (heuristics == HR_BULK_REVOKE)) { 674 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 675 } 676 } 677 clean_up_cached_monitor_info(); 678 } 679 680 681 void BiasedLocking::preserve_marks() { 682 if (!UseBiasedLocking) 683 return; 684 685 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 686 687 assert(_preserved_oop_stack == NULL, "double initialization"); 688 assert(_preserved_mark_stack == NULL, "double initialization"); 689 690 // In order to reduce the number of mark words preserved during GC 691 // due to the presence of biased locking, we reinitialize most mark 692 // words to the class's prototype during GC -- even those which have 693 // a currently valid bias owner. One important situation where we 694 // must not clobber a bias is when a biased object is currently 695 // locked. To handle this case we iterate over the currently-locked 696 // monitors in a prepass and, if they are biased, preserve their 697 // mark words here. This should be a relatively small set of objects 698 // especially compared to the number of objects in the heap. 699 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true); 700 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 701 702 ResourceMark rm; 703 Thread* cur = Thread::current(); 704 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { 705 if (thread->has_last_Java_frame()) { 706 RegisterMap rm(thread); 707 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 708 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 709 if (monitors != NULL) { 710 int len = monitors->length(); 711 // Walk monitors youngest to oldest 712 for (int i = len - 1; i >= 0; i--) { 713 MonitorInfo* mon_info = monitors->at(i); 714 if (mon_info->owner_is_scalar_replaced()) continue; 715 oop owner = mon_info->owner(); 716 assert(owner == oopDesc::bs()->read_barrier(owner), "expect to-space copy"); 717 if (owner != NULL) { 718 markOop mark = owner->mark(); 719 if (mark->has_bias_pattern()) { 720 _preserved_oop_stack->push(Handle(cur, owner)); 721 _preserved_mark_stack->push(mark); 722 } 723 } 724 } 725 } 726 } 727 } 728 } 729 } 730 731 732 void BiasedLocking::restore_marks() { 733 if (!UseBiasedLocking) 734 return; 735 736 assert(_preserved_oop_stack != NULL, "double free"); 737 assert(_preserved_mark_stack != NULL, "double free"); 738 739 int len = _preserved_oop_stack->length(); 740 for (int i = 0; i < len; i++) { 741 Handle owner = _preserved_oop_stack->at(i); 742 markOop mark = _preserved_mark_stack->at(i); 743 owner->set_mark(mark); 744 } 745 746 delete _preserved_oop_stack; 747 _preserved_oop_stack = NULL; 748 delete _preserved_mark_stack; 749 _preserved_mark_stack = NULL; 750 } 751 752 753 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 754 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 755 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 756 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 757 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 758 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 759 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 760 761 762 // BiasedLockingCounters 763 764 int BiasedLockingCounters::slow_path_entry_count() { 765 if (_slow_path_entry_count != 0) { 766 return _slow_path_entry_count; 767 } 768 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 769 _rebiased_lock_entry_count + _revoked_lock_entry_count + 770 _fast_path_entry_count; 771 772 return _total_entry_count - sum; 773 } 774 775 void BiasedLockingCounters::print_on(outputStream* st) { 776 tty->print_cr("# total entries: %d", _total_entry_count); 777 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 778 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 779 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 780 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 781 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 782 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 783 }