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/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 #include "jfr/support/jfrThreadId.hpp" 35 #include "jfr/jfrEvents.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 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL, 148 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization). 149 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { 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 // If requested, return information on which thread held the bias 260 if (biased_locker != NULL) { 261 *biased_locker = biased_thread; 262 } 263 264 return BiasedLocking::BIAS_REVOKED; 265 } 266 267 268 enum HeuristicsResult { 269 HR_NOT_BIASED = 1, 270 HR_SINGLE_REVOKE = 2, 271 HR_BULK_REBIAS = 3, 272 HR_BULK_REVOKE = 4 273 }; 274 275 276 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { 277 markOop mark = o->mark(); 278 if (!mark->has_bias_pattern()) { 279 return HR_NOT_BIASED; 280 } 281 282 // Heuristics to attempt to throttle the number of revocations. 283 // Stages: 284 // 1. Revoke the biases of all objects in the heap of this type, 285 // but allow rebiasing of those objects if unlocked. 286 // 2. Revoke the biases of all objects in the heap of this type 287 // and don't allow rebiasing of these objects. Disable 288 // allocation of objects of that type with the bias bit set. 289 Klass* k = o->klass(); 290 jlong cur_time = os::javaTimeMillis(); 291 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 292 int revocation_count = k->biased_lock_revocation_count(); 293 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 294 (revocation_count < BiasedLockingBulkRevokeThreshold) && 295 (last_bulk_revocation_time != 0) && 296 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 297 // This is the first revocation we've seen in a while of an 298 // object of this type since the last time we performed a bulk 299 // rebiasing operation. The application is allocating objects in 300 // bulk which are biased toward a thread and then handing them 301 // off to another thread. We can cope with this allocation 302 // pattern via the bulk rebiasing mechanism so we reset the 303 // klass's revocation count rather than allow it to increase 304 // monotonically. If we see the need to perform another bulk 305 // rebias operation later, we will, and if subsequently we see 306 // many more revocation operations in a short period of time we 307 // will completely disable biasing for this type. 308 k->set_biased_lock_revocation_count(0); 309 revocation_count = 0; 310 } 311 312 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 313 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 314 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 315 } 316 317 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 318 return HR_BULK_REVOKE; 319 } 320 321 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 322 return HR_BULK_REBIAS; 323 } 324 325 return HR_SINGLE_REVOKE; 326 } 327 328 329 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, 330 bool bulk_rebias, 331 bool attempt_rebias_of_object, 332 JavaThread* requesting_thread) { 333 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 334 335 if (TraceBiasedLocking) { 336 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " 337 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 338 (bulk_rebias ? "rebias" : "revoke"), 339 p2i((void *) o), (intptr_t) o->mark(), o->klass()->external_name()); 340 } 341 342 jlong cur_time = os::javaTimeMillis(); 343 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 344 345 346 Klass* k_o = o->klass(); 347 Klass* klass = k_o; 348 349 if (bulk_rebias) { 350 // Use the epoch in the klass of the object to implicitly revoke 351 // all biases of objects of this data type and force them to be 352 // reacquired. However, we also need to walk the stacks of all 353 // threads and update the headers of lightweight locked objects 354 // with biases to have the current epoch. 355 356 // If the prototype header doesn't have the bias pattern, don't 357 // try to update the epoch -- assume another VM operation came in 358 // and reset the header to the unbiased state, which will 359 // implicitly cause all existing biases to be revoked 360 if (klass->prototype_header()->has_bias_pattern()) { 361 int prev_epoch = klass->prototype_header()->bias_epoch(); 362 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); 363 int cur_epoch = klass->prototype_header()->bias_epoch(); 364 365 // Now walk all threads' stacks and adjust epochs of any biased 366 // and locked objects of this data type we encounter 367 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 368 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 369 for (int i = 0; i < cached_monitor_info->length(); i++) { 370 MonitorInfo* mon_info = cached_monitor_info->at(i); 371 oop owner = mon_info->owner(); 372 markOop mark = owner->mark(); 373 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 374 // We might have encountered this object already in the case of recursive locking 375 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 376 owner->set_mark(mark->set_bias_epoch(cur_epoch)); 377 } 378 } 379 } 380 } 381 382 // At this point we're done. All we have to do is potentially 383 // adjust the header of the given object to revoke its bias. 384 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL); 385 } else { 386 if (TraceBiasedLocking) { 387 ResourceMark rm; 388 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); 389 } 390 391 // Disable biased locking for this data type. Not only will this 392 // cause future instances to not be biased, but existing biased 393 // instances will notice that this implicitly caused their biases 394 // to be revoked. 395 klass->set_prototype_header(markOopDesc::prototype()); 396 397 // Now walk all threads' stacks and forcibly revoke the biases of 398 // any locked and biased objects of this data type we encounter. 399 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 400 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 401 for (int i = 0; i < cached_monitor_info->length(); i++) { 402 MonitorInfo* mon_info = cached_monitor_info->at(i); 403 oop owner = mon_info->owner(); 404 markOop mark = owner->mark(); 405 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 406 revoke_bias(owner, false, true, requesting_thread, NULL); 407 } 408 } 409 } 410 411 // Must force the bias of the passed object to be forcibly revoked 412 // as well to ensure guarantees to callers 413 revoke_bias(o, false, true, requesting_thread, NULL); 414 } 415 416 if (TraceBiasedLocking) { 417 tty->print_cr("* Ending bulk revocation"); 418 } 419 420 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; 421 422 if (attempt_rebias_of_object && 423 o->mark()->has_bias_pattern() && 424 klass->prototype_header()->has_bias_pattern()) { 425 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), 426 klass->prototype_header()->bias_epoch()); 427 o->set_mark(new_mark); 428 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; 429 if (TraceBiasedLocking) { 430 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 431 } 432 } 433 434 assert(!o->mark()->has_bias_pattern() || 435 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), 436 "bug in bulk bias revocation"); 437 438 return status_code; 439 } 440 441 442 static void clean_up_cached_monitor_info() { 443 // Walk the thread list clearing out the cached monitors 444 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 445 thr->set_cached_monitor_info(NULL); 446 } 447 } 448 449 450 class VM_RevokeBias : public VM_Operation { 451 protected: 452 Handle* _obj; 453 GrowableArray<Handle>* _objs; 454 JavaThread* _requesting_thread; 455 BiasedLocking::Condition _status_code; 456 traceid _biased_locker_id; 457 458 public: 459 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) 460 : _obj(obj) 461 , _objs(NULL) 462 , _requesting_thread(requesting_thread) 463 , _status_code(BiasedLocking::NOT_BIASED) 464 , _biased_locker_id(0) {} 465 466 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) 467 : _obj(NULL) 468 , _objs(objs) 469 , _requesting_thread(requesting_thread) 470 , _status_code(BiasedLocking::NOT_BIASED) 471 , _biased_locker_id(0) {} 472 473 virtual VMOp_Type type() const { return VMOp_RevokeBias; } 474 475 virtual bool doit_prologue() { 476 // Verify that there is actual work to do since the callers just 477 // give us locked object(s). If we don't find any biased objects 478 // there is nothing to do and we avoid a safepoint. 479 if (_obj != NULL) { 480 markOop mark = (*_obj)()->mark(); 481 if (mark->has_bias_pattern()) { 482 return true; 483 } 484 } else { 485 for ( int i = 0 ; i < _objs->length(); i++ ) { 486 markOop mark = (_objs->at(i))()->mark(); 487 if (mark->has_bias_pattern()) { 488 return true; 489 } 490 } 491 } 492 return false; 493 } 494 495 virtual void doit() { 496 if (_obj != NULL) { 497 if (TraceBiasedLocking) { 498 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); 499 } 500 JavaThread* biased_locker = NULL; 501 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker); 502 if (biased_locker != NULL) { 503 _biased_locker_id = JFR_THREAD_ID(biased_locker); 504 } 505 clean_up_cached_monitor_info(); 506 return; 507 } else { 508 if (TraceBiasedLocking) { 509 tty->print_cr("Revoking bias with global safepoint:"); 510 } 511 BiasedLocking::revoke_at_safepoint(_objs); 512 } 513 } 514 515 BiasedLocking::Condition status_code() const { 516 return _status_code; 517 } 518 519 traceid biased_locker() const { 520 return _biased_locker_id; 521 } 522 }; 523 524 525 class VM_BulkRevokeBias : public VM_RevokeBias { 526 private: 527 bool _bulk_rebias; 528 bool _attempt_rebias_of_object; 529 530 public: 531 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 532 bool bulk_rebias, 533 bool attempt_rebias_of_object) 534 : VM_RevokeBias(obj, requesting_thread) 535 , _bulk_rebias(bulk_rebias) 536 , _attempt_rebias_of_object(attempt_rebias_of_object) {} 537 538 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 539 virtual bool doit_prologue() { return true; } 540 541 virtual void doit() { 542 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 543 clean_up_cached_monitor_info(); 544 } 545 }; 546 547 548 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 549 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 550 551 // We can revoke the biases of anonymously-biased objects 552 // efficiently enough that we should not cause these revocations to 553 // update the heuristics because doing so may cause unwanted bulk 554 // revocations (which are expensive) to occur. 555 markOop mark = obj->mark(); 556 if (mark->is_biased_anonymously() && !attempt_rebias) { 557 // We are probably trying to revoke the bias of this object due to 558 // an identity hash code computation. Try to revoke the bias 559 // without a safepoint. This is possible if we can successfully 560 // compare-and-exchange an unbiased header into the mark word of 561 // the object, meaning that no other thread has raced to acquire 562 // the bias of the object. 563 markOop biased_value = mark; 564 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 565 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 566 if (res_mark == biased_value) { 567 return BIAS_REVOKED; 568 } 569 } else if (mark->has_bias_pattern()) { 570 Klass* k = obj->klass(); 571 markOop prototype_header = k->prototype_header(); 572 if (!prototype_header->has_bias_pattern()) { 573 // This object has a stale bias from before the bulk revocation 574 // for this data type occurred. It's pointless to update the 575 // heuristics at this point so simply update the header with a 576 // CAS. If we fail this race, the object's bias has been revoked 577 // by another thread so we simply return and let the caller deal 578 // with it. 579 markOop biased_value = mark; 580 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); 581 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); 582 return BIAS_REVOKED; 583 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { 584 // The epoch of this biasing has expired indicating that the 585 // object is effectively unbiased. Depending on whether we need 586 // to rebias or revoke the bias of this object we can do it 587 // efficiently enough with a CAS that we shouldn't update the 588 // heuristics. This is normally done in the assembly code but we 589 // can reach this point due to various points in the runtime 590 // needing to revoke biases. 591 if (attempt_rebias) { 592 assert(THREAD->is_Java_thread(), ""); 593 markOop biased_value = mark; 594 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); 595 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); 596 if (res_mark == biased_value) { 597 return BIAS_REVOKED_AND_REBIASED; 598 } 599 } else { 600 markOop biased_value = mark; 601 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 602 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); 603 if (res_mark == biased_value) { 604 return BIAS_REVOKED; 605 } 606 } 607 } 608 } 609 610 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); 611 if (heuristics == HR_NOT_BIASED) { 612 return NOT_BIASED; 613 } else if (heuristics == HR_SINGLE_REVOKE) { 614 Klass *k = obj->klass(); 615 markOop prototype_header = k->prototype_header(); 616 if (mark->biased_locker() == THREAD && 617 prototype_header->bias_epoch() == mark->bias_epoch()) { 618 // A thread is trying to revoke the bias of an object biased 619 // toward it, again likely due to an identity hash code 620 // computation. We can again avoid a safepoint in this case 621 // since we are only going to walk our own stack. There are no 622 // races with revocations occurring in other threads because we 623 // reach no safepoints in the revocation path. 624 // Also check the epoch because even if threads match, another thread 625 // can come in with a CAS to steal the bias of an object that has a 626 // stale epoch. 627 ResourceMark rm; 628 if (TraceBiasedLocking) { 629 tty->print_cr("Revoking bias by walking my own stack:"); 630 } 631 EventBiasedLockSelfRevocation event; 632 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL); 633 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); 634 assert(cond == BIAS_REVOKED, "why not?"); 635 if (event.should_commit()) { 636 event.set_lockClass(k); 637 event.commit(); 638 } 639 return cond; 640 } else { 641 EventBiasedLockRevocation event; 642 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); 643 VMThread::execute(&revoke); 644 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) { 645 event.set_lockClass(k); 646 // Subtract 1 to match the id of events committed inside the safepoint 647 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1); 648 event.set_previousOwner(revoke.biased_locker()); 649 event.commit(); 650 } 651 return revoke.status_code(); 652 } 653 } 654 655 assert((heuristics == HR_BULK_REVOKE) || 656 (heuristics == HR_BULK_REBIAS), "?"); 657 EventBiasedLockClassRevocation event; 658 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, 659 (heuristics == HR_BULK_REBIAS), 660 attempt_rebias); 661 VMThread::execute(&bulk_revoke); 662 if (event.should_commit()) { 663 event.set_revokedClass(obj->klass()); 664 event.set_disableBiasing((heuristics != HR_BULK_REBIAS)); 665 // Subtract 1 to match the id of events committed inside the safepoint 666 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1); 667 event.commit(); 668 } 669 return bulk_revoke.status_code(); 670 } 671 672 673 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { 674 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 675 if (objs->length() == 0) { 676 return; 677 } 678 VM_RevokeBias revoke(objs, JavaThread::current()); 679 VMThread::execute(&revoke); 680 } 681 682 683 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 684 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 685 oop obj = h_obj(); 686 HeuristicsResult heuristics = update_heuristics(obj, false); 687 if (heuristics == HR_SINGLE_REVOKE) { 688 revoke_bias(obj, false, false, NULL, NULL); 689 } else if ((heuristics == HR_BULK_REBIAS) || 690 (heuristics == HR_BULK_REVOKE)) { 691 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 692 } 693 clean_up_cached_monitor_info(); 694 } 695 696 697 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 698 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 699 int len = objs->length(); 700 for (int i = 0; i < len; i++) { 701 oop obj = (objs->at(i))(); 702 HeuristicsResult heuristics = update_heuristics(obj, false); 703 if (heuristics == HR_SINGLE_REVOKE) { 704 revoke_bias(obj, false, false, NULL, NULL); 705 } else if ((heuristics == HR_BULK_REBIAS) || 706 (heuristics == HR_BULK_REVOKE)) { 707 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 708 } 709 } 710 clean_up_cached_monitor_info(); 711 } 712 713 714 void BiasedLocking::preserve_marks() { 715 if (!UseBiasedLocking) 716 return; 717 718 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 719 720 assert(_preserved_oop_stack == NULL, "double initialization"); 721 assert(_preserved_mark_stack == NULL, "double initialization"); 722 723 // In order to reduce the number of mark words preserved during GC 724 // due to the presence of biased locking, we reinitialize most mark 725 // words to the class's prototype during GC -- even those which have 726 // a currently valid bias owner. One important situation where we 727 // must not clobber a bias is when a biased object is currently 728 // locked. To handle this case we iterate over the currently-locked 729 // monitors in a prepass and, if they are biased, preserve their 730 // mark words here. This should be a relatively small set of objects 731 // especially compared to the number of objects in the heap. 732 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true); 733 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 734 735 ResourceMark rm; 736 Thread* cur = Thread::current(); 737 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { 738 if (thread->has_last_Java_frame()) { 739 RegisterMap rm(thread); 740 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 741 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 742 if (monitors != NULL) { 743 int len = monitors->length(); 744 // Walk monitors youngest to oldest 745 for (int i = len - 1; i >= 0; i--) { 746 MonitorInfo* mon_info = monitors->at(i); 747 if (mon_info->owner_is_scalar_replaced()) continue; 748 oop owner = mon_info->owner(); 749 if (owner != NULL) { 750 markOop mark = owner->mark(); 751 if (mark->has_bias_pattern()) { 752 _preserved_oop_stack->push(Handle(cur, owner)); 753 _preserved_mark_stack->push(mark); 754 } 755 } 756 } 757 } 758 } 759 } 760 } 761 } 762 763 764 void BiasedLocking::restore_marks() { 765 if (!UseBiasedLocking) 766 return; 767 768 assert(_preserved_oop_stack != NULL, "double free"); 769 assert(_preserved_mark_stack != NULL, "double free"); 770 771 int len = _preserved_oop_stack->length(); 772 for (int i = 0; i < len; i++) { 773 Handle owner = _preserved_oop_stack->at(i); 774 markOop mark = _preserved_mark_stack->at(i); 775 owner->set_mark(mark); 776 } 777 778 delete _preserved_oop_stack; 779 _preserved_oop_stack = NULL; 780 delete _preserved_mark_stack; 781 _preserved_mark_stack = NULL; 782 } 783 784 785 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 786 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 787 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 788 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 789 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 790 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 791 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 792 793 794 // BiasedLockingCounters 795 796 int BiasedLockingCounters::slow_path_entry_count() { 797 if (_slow_path_entry_count != 0) { 798 return _slow_path_entry_count; 799 } 800 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 801 _rebiased_lock_entry_count + _revoked_lock_entry_count + 802 _fast_path_entry_count; 803 804 return _total_entry_count - sum; 805 } 806 807 void BiasedLockingCounters::print_on(outputStream* st) { 808 tty->print_cr("# total entries: %d", _total_entry_count); 809 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 810 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 811 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 812 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 813 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 814 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 815 }