1 /* 2 * Copyright (c) 2005, 2020, 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 "classfile/classLoaderDataGraph.hpp" 27 #include "jfr/jfrEvents.hpp" 28 #include "jfr/support/jfrThreadId.hpp" 29 #include "logging/log.hpp" 30 #include "memory/resourceArea.hpp" 31 #include "oops/klass.inline.hpp" 32 #include "oops/markWord.hpp" 33 #include "oops/oop.inline.hpp" 34 #include "runtime/atomic.hpp" 35 #include "runtime/basicLock.hpp" 36 #include "runtime/biasedLocking.hpp" 37 #include "runtime/handles.inline.hpp" 38 #include "runtime/handshake.hpp" 39 #include "runtime/safepointMechanism.hpp" 40 #include "runtime/task.hpp" 41 #include "runtime/threadSMR.hpp" 42 #include "runtime/vframe.hpp" 43 #include "runtime/vmThread.hpp" 44 #include "runtime/vmOperations.hpp" 45 46 47 static bool _biased_locking_enabled = false; 48 BiasedLockingCounters BiasedLocking::_counters; 49 50 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 51 static GrowableArray<markWord>* _preserved_mark_stack = NULL; 52 53 static void enable_biased_locking(InstanceKlass* k) { 54 k->set_prototype_header(markWord::biased_locking_prototype()); 55 } 56 57 static void enable_biased_locking() { 58 _biased_locking_enabled = true; 59 log_info(biasedlocking)("Biased locking enabled"); 60 } 61 62 class VM_EnableBiasedLocking: public VM_Operation { 63 public: 64 VM_EnableBiasedLocking() {} 65 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 66 67 void doit() { 68 // Iterate the class loader data dictionaries enabling biased locking for all 69 // currently loaded classes. 70 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking); 71 // Indicate that future instances should enable it as well 72 enable_biased_locking(); 73 } 74 75 bool allow_nested_vm_operations() const { return false; } 76 }; 77 78 79 // One-shot PeriodicTask subclass for enabling biased locking 80 class EnableBiasedLockingTask : public PeriodicTask { 81 public: 82 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 83 84 virtual void task() { 85 VM_EnableBiasedLocking op; 86 VMThread::execute(&op); 87 88 // Reclaim our storage and disenroll ourself 89 delete this; 90 } 91 }; 92 93 94 void BiasedLocking::init() { 95 // If biased locking is enabled and BiasedLockingStartupDelay is set, 96 // schedule a task to fire after the specified delay which turns on 97 // biased locking for all currently loaded classes as well as future 98 // ones. This could be a workaround for startup time regressions 99 // due to large number of safepoints being taken during VM startup for 100 // bias revocation. 101 if (UseBiasedLocking) { 102 if (BiasedLockingStartupDelay > 0) { 103 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 104 task->enroll(); 105 } else { 106 enable_biased_locking(); 107 } 108 } 109 } 110 111 112 bool BiasedLocking::enabled() { 113 assert(UseBiasedLocking, "precondition"); 114 // We check "BiasedLockingStartupDelay == 0" here to cover the 115 // possibility of calls to BiasedLocking::enabled() before 116 // BiasedLocking::init(). 117 return _biased_locking_enabled || BiasedLockingStartupDelay == 0; 118 } 119 120 121 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 122 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 123 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 124 if (info != NULL) { 125 return info; 126 } 127 128 info = new GrowableArray<MonitorInfo*>(); 129 130 // It's possible for the thread to not have any Java frames on it, 131 // i.e., if it's the main thread and it's already returned from main() 132 if (thread->has_last_Java_frame()) { 133 RegisterMap rm(thread); 134 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 135 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 136 if (monitors != NULL) { 137 int len = monitors->length(); 138 // Walk monitors youngest to oldest 139 for (int i = len - 1; i >= 0; i--) { 140 MonitorInfo* mon_info = monitors->at(i); 141 if (mon_info->eliminated()) continue; 142 oop owner = mon_info->owner(); 143 if (owner != NULL) { 144 info->append(mon_info); 145 } 146 } 147 } 148 } 149 } 150 151 thread->set_cached_monitor_info(info); 152 return info; 153 } 154 155 156 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL, 157 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization). 158 void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { 159 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 160 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 161 162 markWord mark = obj->mark(); 163 if (!mark.has_bias_pattern()) { 164 if (log_is_enabled(Info, biasedlocking)) { 165 ResourceMark rm; 166 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT 167 ", mark " INTPTR_FORMAT ", type %s" 168 ", requesting thread " INTPTR_FORMAT 169 " because it's no longer biased)", 170 p2i((void *)obj), mark.value(), 171 obj->klass()->external_name(), 172 (intptr_t) requesting_thread); 173 } 174 return; 175 } 176 177 uint age = mark.age(); 178 markWord unbiased_prototype = markWord::prototype().set_age(age); 179 180 // Log at "info" level if not bulk, else "trace" level 181 if (!is_bulk) { 182 ResourceMark rm; 183 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark " 184 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 185 ", requesting thread " INTPTR_FORMAT, 186 p2i((void *)obj), 187 mark.value(), 188 obj->klass()->external_name(), 189 obj->klass()->prototype_header().value(), 190 (intptr_t) requesting_thread); 191 } else { 192 ResourceMark rm; 193 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark " 194 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT 195 " , requesting thread " INTPTR_FORMAT, 196 p2i((void *)obj), 197 mark.value(), 198 obj->klass()->external_name(), 199 obj->klass()->prototype_header().value(), 200 (intptr_t) requesting_thread); 201 } 202 203 JavaThread* biased_thread = mark.biased_locker(); 204 if (biased_thread == NULL) { 205 // Object is anonymously biased. We can get here if, for 206 // example, we revoke the bias due to an identity hash code 207 // being computed for an object. 208 obj->set_mark(unbiased_prototype); 209 210 // Log at "info" level if not bulk, else "trace" level 211 if (!is_bulk) { 212 log_info(biasedlocking)(" Revoked bias of anonymously-biased object"); 213 } else { 214 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object"); 215 } 216 return; 217 } 218 219 // Handle case where the thread toward which the object was biased has exited 220 bool thread_is_alive = false; 221 if (requesting_thread == biased_thread) { 222 thread_is_alive = true; 223 } else { 224 ThreadsListHandle tlh; 225 thread_is_alive = tlh.includes(biased_thread); 226 } 227 if (!thread_is_alive) { 228 obj->set_mark(unbiased_prototype); 229 // Log at "info" level if not bulk, else "trace" level 230 if (!is_bulk) { 231 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread (" 232 PTR_FORMAT ")", p2i(biased_thread)); 233 } else { 234 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread (" 235 PTR_FORMAT ")", p2i(biased_thread)); 236 } 237 return; 238 } 239 240 // Log at "info" level if not bulk, else "trace" level 241 if (!is_bulk) { 242 log_info(biasedlocking)(" Revoked bias of object biased toward live thread (" 243 PTR_FORMAT ")", p2i(biased_thread)); 244 } else { 245 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread (" 246 PTR_FORMAT ")", p2i(biased_thread)); 247 } 248 249 // Thread owning bias is alive. 250 // Check to see whether it currently owns the lock and, if so, 251 // write down the needed displaced headers to the thread's stack. 252 // Otherwise, restore the object's header either to the unlocked 253 // or unbiased state. 254 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 255 BasicLock* highest_lock = NULL; 256 for (int i = 0; i < cached_monitor_info->length(); i++) { 257 MonitorInfo* mon_info = cached_monitor_info->at(i); 258 if (mon_info->owner() == obj) { 259 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 260 p2i((void *) mon_info->owner()), 261 p2i((void *) obj)); 262 // Assume recursive case and fix up highest lock below 263 markWord mark = markWord::encode((BasicLock*) NULL); 264 highest_lock = mon_info->lock(); 265 highest_lock->set_displaced_header(mark); 266 } else { 267 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 268 p2i((void *) mon_info->owner()), 269 p2i((void *) obj)); 270 } 271 } 272 if (highest_lock != NULL) { 273 // Fix up highest lock to contain displaced header and point 274 // object at it 275 highest_lock->set_displaced_header(unbiased_prototype); 276 // Reset object header to point to displaced mark. 277 // Must release store the lock address for platforms without TSO 278 // ordering (e.g. ppc). 279 obj->release_set_mark(markWord::encode(highest_lock)); 280 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 281 // Log at "info" level if not bulk, else "trace" level 282 if (!is_bulk) { 283 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 284 } else { 285 log_trace(biasedlocking)(" Revoked bias of currently-locked object"); 286 } 287 } else { 288 // Log at "info" level if not bulk, else "trace" level 289 if (!is_bulk) { 290 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 291 } else { 292 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object"); 293 } 294 // Store the unlocked value into the object's header. 295 obj->set_mark(unbiased_prototype); 296 } 297 298 // If requested, return information on which thread held the bias 299 if (biased_locker != NULL) { 300 *biased_locker = biased_thread; 301 } 302 } 303 304 305 enum HeuristicsResult { 306 HR_NOT_BIASED = 1, 307 HR_SINGLE_REVOKE = 2, 308 HR_BULK_REBIAS = 3, 309 HR_BULK_REVOKE = 4 310 }; 311 312 313 static HeuristicsResult update_heuristics(oop o) { 314 markWord mark = o->mark(); 315 if (!mark.has_bias_pattern()) { 316 return HR_NOT_BIASED; 317 } 318 319 // Heuristics to attempt to throttle the number of revocations. 320 // Stages: 321 // 1. Revoke the biases of all objects in the heap of this type, 322 // but allow rebiasing of those objects if unlocked. 323 // 2. Revoke the biases of all objects in the heap of this type 324 // and don't allow rebiasing of these objects. Disable 325 // allocation of objects of that type with the bias bit set. 326 Klass* k = o->klass(); 327 jlong cur_time = os::javaTimeMillis(); 328 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 329 int revocation_count = k->biased_lock_revocation_count(); 330 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 331 (revocation_count < BiasedLockingBulkRevokeThreshold) && 332 (last_bulk_revocation_time != 0) && 333 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 334 // This is the first revocation we've seen in a while of an 335 // object of this type since the last time we performed a bulk 336 // rebiasing operation. The application is allocating objects in 337 // bulk which are biased toward a thread and then handing them 338 // off to another thread. We can cope with this allocation 339 // pattern via the bulk rebiasing mechanism so we reset the 340 // klass's revocation count rather than allow it to increase 341 // monotonically. If we see the need to perform another bulk 342 // rebias operation later, we will, and if subsequently we see 343 // many more revocation operations in a short period of time we 344 // will completely disable biasing for this type. 345 k->set_biased_lock_revocation_count(0); 346 revocation_count = 0; 347 } 348 349 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 350 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 351 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 352 } 353 354 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 355 return HR_BULK_REVOKE; 356 } 357 358 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 359 return HR_BULK_REBIAS; 360 } 361 362 return HR_SINGLE_REVOKE; 363 } 364 365 366 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) { 367 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 368 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 369 370 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object " 371 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 372 (bulk_rebias ? "rebias" : "revoke"), 373 p2i((void *) o), 374 o->mark().value(), 375 o->klass()->external_name()); 376 377 jlong cur_time = os::javaTimeMillis(); 378 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 379 380 Klass* k_o = o->klass(); 381 Klass* klass = k_o; 382 383 { 384 JavaThreadIteratorWithHandle jtiwh; 385 386 if (bulk_rebias) { 387 // Use the epoch in the klass of the object to implicitly revoke 388 // all biases of objects of this data type and force them to be 389 // reacquired. However, we also need to walk the stacks of all 390 // threads and update the headers of lightweight locked objects 391 // with biases to have the current epoch. 392 393 // If the prototype header doesn't have the bias pattern, don't 394 // try to update the epoch -- assume another VM operation came in 395 // and reset the header to the unbiased state, which will 396 // implicitly cause all existing biases to be revoked 397 if (klass->prototype_header().has_bias_pattern()) { 398 int prev_epoch = klass->prototype_header().bias_epoch(); 399 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch()); 400 int cur_epoch = klass->prototype_header().bias_epoch(); 401 402 // Now walk all threads' stacks and adjust epochs of any biased 403 // and locked objects of this data type we encounter 404 for (; JavaThread *thr = jtiwh.next(); ) { 405 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 406 for (int i = 0; i < cached_monitor_info->length(); i++) { 407 MonitorInfo* mon_info = cached_monitor_info->at(i); 408 oop owner = mon_info->owner(); 409 markWord mark = owner->mark(); 410 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 411 // We might have encountered this object already in the case of recursive locking 412 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 413 owner->set_mark(mark.set_bias_epoch(cur_epoch)); 414 } 415 } 416 } 417 } 418 419 // At this point we're done. All we have to do is potentially 420 // adjust the header of the given object to revoke its bias. 421 single_revoke_at_safepoint(o, true, requesting_thread, NULL); 422 } else { 423 if (log_is_enabled(Info, biasedlocking)) { 424 ResourceMark rm; 425 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name()); 426 } 427 428 // Disable biased locking for this data type. Not only will this 429 // cause future instances to not be biased, but existing biased 430 // instances will notice that this implicitly caused their biases 431 // to be revoked. 432 klass->set_prototype_header(markWord::prototype()); 433 434 // Now walk all threads' stacks and forcibly revoke the biases of 435 // any locked and biased objects of this data type we encounter. 436 for (; JavaThread *thr = jtiwh.next(); ) { 437 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 438 for (int i = 0; i < cached_monitor_info->length(); i++) { 439 MonitorInfo* mon_info = cached_monitor_info->at(i); 440 oop owner = mon_info->owner(); 441 markWord mark = owner->mark(); 442 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 443 single_revoke_at_safepoint(owner, true, requesting_thread, NULL); 444 } 445 } 446 } 447 448 // Must force the bias of the passed object to be forcibly revoked 449 // as well to ensure guarantees to callers 450 single_revoke_at_safepoint(o, true, requesting_thread, NULL); 451 } 452 } // ThreadsListHandle is destroyed here. 453 454 log_info(biasedlocking)("* Ending bulk revocation"); 455 456 assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation"); 457 } 458 459 460 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) { 461 if (thread != NULL) { 462 thread->set_cached_monitor_info(NULL); 463 } else { 464 // Walk the thread list clearing out the cached monitors 465 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 466 thr->set_cached_monitor_info(NULL); 467 } 468 } 469 } 470 471 472 class VM_BulkRevokeBias : public VM_Operation { 473 private: 474 Handle* _obj; 475 JavaThread* _requesting_thread; 476 bool _bulk_rebias; 477 uint64_t _safepoint_id; 478 479 public: 480 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 481 bool bulk_rebias) 482 : _obj(obj) 483 , _requesting_thread(requesting_thread) 484 , _bulk_rebias(bulk_rebias) 485 , _safepoint_id(0) {} 486 487 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 488 489 virtual void doit() { 490 BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread); 491 _safepoint_id = SafepointSynchronize::safepoint_id(); 492 clean_up_cached_monitor_info(); 493 } 494 495 bool is_bulk_rebias() const { 496 return _bulk_rebias; 497 } 498 499 uint64_t safepoint_id() const { 500 return _safepoint_id; 501 } 502 }; 503 504 505 class RevokeOneBias : public HandshakeClosure { 506 protected: 507 Handle _obj; 508 JavaThread* _requesting_thread; 509 JavaThread* _biased_locker; 510 BiasedLocking::Condition _status_code; 511 traceid _biased_locker_id; 512 513 public: 514 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker) 515 : HandshakeClosure("RevokeOneBias") 516 , _obj(obj) 517 , _requesting_thread(requesting_thread) 518 , _biased_locker(biased_locker) 519 , _status_code(BiasedLocking::NOT_BIASED) 520 , _biased_locker_id(0) {} 521 522 void do_thread(Thread* target) { 523 assert(target == _biased_locker, "Wrong thread"); 524 525 oop o = _obj(); 526 markWord mark = o->mark(); 527 528 if (!mark.has_bias_pattern()) { 529 return; 530 } 531 532 markWord prototype = o->klass()->prototype_header(); 533 if (!prototype.has_bias_pattern()) { 534 // This object has a stale bias from before the handshake 535 // was requested. If we fail this race, the object's bias 536 // has been revoked by another thread so we simply return. 537 markWord biased_value = mark; 538 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 539 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 540 if (biased_value == mark) { 541 _status_code = BiasedLocking::BIAS_REVOKED; 542 } 543 return; 544 } 545 546 if (_biased_locker == mark.biased_locker()) { 547 if (mark.bias_epoch() == prototype.bias_epoch()) { 548 // Epoch is still valid. This means biaser could be currently 549 // synchronized on this object. We must walk its stack looking 550 // for monitor records associated with this object and change 551 // them to be stack locks if any are found. 552 ResourceMark rm; 553 BiasedLocking::walk_stack_and_revoke(o, _biased_locker); 554 _biased_locker->set_cached_monitor_info(NULL); 555 assert(!o->mark().has_bias_pattern(), "invariant"); 556 _biased_locker_id = JFR_THREAD_ID(_biased_locker); 557 _status_code = BiasedLocking::BIAS_REVOKED; 558 return; 559 } else { 560 markWord biased_value = mark; 561 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 562 if (mark == biased_value || !mark.has_bias_pattern()) { 563 assert(!o->mark().has_bias_pattern(), "should be revoked"); 564 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED; 565 return; 566 } 567 } 568 } 569 570 _status_code = BiasedLocking::NOT_REVOKED; 571 } 572 573 BiasedLocking::Condition status_code() const { 574 return _status_code; 575 } 576 577 traceid biased_locker() const { 578 return _biased_locker_id; 579 } 580 }; 581 582 583 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) { 584 assert(event != NULL, "invariant"); 585 assert(k != NULL, "invariant"); 586 assert(event->should_commit(), "invariant"); 587 event->set_lockClass(k); 588 event->commit(); 589 } 590 591 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) { 592 assert(event != NULL, "invariant"); 593 assert(k != NULL, "invariant"); 594 assert(op != NULL, "invariant"); 595 assert(event->should_commit(), "invariant"); 596 event->set_lockClass(k); 597 event->set_safepointId(0); 598 event->set_previousOwner(op->biased_locker()); 599 event->commit(); 600 } 601 602 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) { 603 assert(event != NULL, "invariant"); 604 assert(k != NULL, "invariant"); 605 assert(op != NULL, "invariant"); 606 assert(event->should_commit(), "invariant"); 607 event->set_revokedClass(k); 608 event->set_disableBiasing(!op->is_bulk_rebias()); 609 event->set_safepointId(op->safepoint_id()); 610 event->commit(); 611 } 612 613 614 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) { 615 616 EventBiasedLockRevocation event; 617 if (PrintBiasedLockingStatistics) { 618 Atomic::inc(handshakes_count_addr()); 619 } 620 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread " 621 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester), 622 p2i(biaser), p2i(obj())); 623 624 RevokeOneBias revoke(obj, requester, biaser); 625 bool executed = Handshake::execute_direct(&revoke, biaser); 626 if (revoke.status_code() == NOT_REVOKED) { 627 return NOT_REVOKED; 628 } 629 if (executed) { 630 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked", 631 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already ")); 632 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) { 633 post_revocation_event(&event, obj->klass(), &revoke); 634 } 635 assert(!obj->mark().has_bias_pattern(), "invariant"); 636 return revoke.status_code(); 637 } else { 638 // Thread was not alive. 639 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly 640 // created JavaThread (that happens to get the same memory address as biaser) synchronizing 641 // on this object. 642 { 643 MutexLocker ml(Threads_lock); 644 markWord mark = obj->mark(); 645 // Check if somebody else was able to revoke it before biased thread exited. 646 if (!mark.has_bias_pattern()) { 647 return NOT_BIASED; 648 } 649 ThreadsListHandle tlh; 650 markWord prototype = obj->klass()->prototype_header(); 651 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() && 652 prototype.bias_epoch() == mark.bias_epoch())) { 653 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 654 if (event.should_commit()) { 655 post_revocation_event(&event, obj->klass(), &revoke); 656 } 657 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now"); 658 return BIAS_REVOKED; 659 } 660 } 661 } 662 663 return NOT_REVOKED; 664 } 665 666 667 // Caller should have instantiated a ResourceMark object before calling this method 668 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) { 669 assert(!SafepointSynchronize::is_at_safepoint() || !SafepointMechanism::uses_thread_local_poll(), 670 "if SafepointMechanism::uses_thread_local_poll() is enabled this should always be executed outside safepoints"); 671 assert(Thread::current() == biased_locker || Thread::current() == biased_locker->get_active_handshaker() || 672 Thread::current()->is_VM_thread(), "wrong thread"); 673 674 markWord mark = obj->mark(); 675 assert(mark.biased_locker() == biased_locker && 676 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant"); 677 678 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark " 679 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 680 ", biaser " INTPTR_FORMAT " %s", 681 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread", 682 p2i(Thread::current()), 683 p2i(obj), 684 mark.value(), 685 obj->klass()->external_name(), 686 obj->klass()->prototype_header().value(), 687 p2i(biased_locker), 688 Thread::current()->is_VM_thread() ? "" : "(walking own stack)"); 689 690 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age()); 691 692 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker); 693 BasicLock* highest_lock = NULL; 694 for (int i = 0; i < cached_monitor_info->length(); i++) { 695 MonitorInfo* mon_info = cached_monitor_info->at(i); 696 if (mon_info->owner() == obj) { 697 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 698 p2i(mon_info->owner()), 699 p2i(obj)); 700 // Assume recursive case and fix up highest lock below 701 markWord mark = markWord::encode((BasicLock*) NULL); 702 highest_lock = mon_info->lock(); 703 highest_lock->set_displaced_header(mark); 704 } else { 705 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 706 p2i(mon_info->owner()), 707 p2i(obj)); 708 } 709 } 710 if (highest_lock != NULL) { 711 // Fix up highest lock to contain displaced header and point 712 // object at it 713 highest_lock->set_displaced_header(unbiased_prototype); 714 // Reset object header to point to displaced mark. 715 // Must release store the lock address for platforms without TSO 716 // ordering (e.g. ppc). 717 obj->release_set_mark(markWord::encode(highest_lock)); 718 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 719 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 720 } else { 721 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 722 // Store the unlocked value into the object's header. 723 obj->set_mark(unbiased_prototype); 724 } 725 726 assert(!obj->mark().has_bias_pattern(), "must not be biased"); 727 } 728 729 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) { 730 assert(THREAD->is_Java_thread(), "must be called by a JavaThread"); 731 JavaThread* thread = (JavaThread*)THREAD; 732 733 markWord mark = obj->mark(); 734 735 if (!mark.has_bias_pattern()) { 736 return; 737 } 738 739 Klass *k = obj->klass(); 740 assert(mark.biased_locker() == thread && 741 k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state"); 742 ResourceMark rm; 743 log_info(biasedlocking)("Revoking bias by walking my own stack:"); 744 EventBiasedLockSelfRevocation event; 745 BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread); 746 thread->set_cached_monitor_info(NULL); 747 assert(!obj->mark().has_bias_pattern(), "invariant"); 748 if (event.should_commit()) { 749 post_self_revocation_event(&event, k); 750 } 751 } 752 753 void BiasedLocking::revoke(Handle obj, TRAPS) { 754 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 755 756 while (true) { 757 // We can revoke the biases of anonymously-biased objects 758 // efficiently enough that we should not cause these revocations to 759 // update the heuristics because doing so may cause unwanted bulk 760 // revocations (which are expensive) to occur. 761 markWord mark = obj->mark(); 762 763 if (!mark.has_bias_pattern()) { 764 return; 765 } 766 767 if (mark.is_biased_anonymously()) { 768 // We are probably trying to revoke the bias of this object due to 769 // an identity hash code computation. Try to revoke the bias 770 // without a safepoint. This is possible if we can successfully 771 // compare-and-exchange an unbiased header into the mark word of 772 // the object, meaning that no other thread has raced to acquire 773 // the bias of the object. 774 markWord biased_value = mark; 775 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 776 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark); 777 if (res_mark == biased_value) { 778 return; 779 } 780 mark = res_mark; // Refresh mark with the latest value. 781 } else { 782 Klass* k = obj->klass(); 783 markWord prototype_header = k->prototype_header(); 784 if (!prototype_header.has_bias_pattern()) { 785 // This object has a stale bias from before the bulk revocation 786 // for this data type occurred. It's pointless to update the 787 // heuristics at this point so simply update the header with a 788 // CAS. If we fail this race, the object's bias has been revoked 789 // by another thread so we simply return and let the caller deal 790 // with it. 791 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark); 792 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 793 return; 794 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) { 795 // The epoch of this biasing has expired indicating that the 796 // object is effectively unbiased. We can revoke the bias of this 797 // object efficiently enough with a CAS that we shouldn't update the 798 // heuristics. This is normally done in the assembly code but we 799 // can reach this point due to various points in the runtime 800 // needing to revoke biases. 801 markWord res_mark; 802 markWord biased_value = mark; 803 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 804 res_mark = obj->cas_set_mark(unbiased_prototype, mark); 805 if (res_mark == biased_value) { 806 return; 807 } 808 mark = res_mark; // Refresh mark with the latest value. 809 } 810 } 811 812 HeuristicsResult heuristics = update_heuristics(obj()); 813 if (heuristics == HR_NOT_BIASED) { 814 return; 815 } else if (heuristics == HR_SINGLE_REVOKE) { 816 JavaThread *blt = mark.biased_locker(); 817 assert(blt != NULL, "invariant"); 818 if (blt == THREAD) { 819 // A thread is trying to revoke the bias of an object biased 820 // toward it, again likely due to an identity hash code 821 // computation. We can again avoid a safepoint/handshake in this case 822 // since we are only going to walk our own stack. There are no 823 // races with revocations occurring in other threads because we 824 // reach no safepoints in the revocation path. 825 EventBiasedLockSelfRevocation event; 826 ResourceMark rm; 827 walk_stack_and_revoke(obj(), blt); 828 blt->set_cached_monitor_info(NULL); 829 assert(!obj->mark().has_bias_pattern(), "invariant"); 830 if (event.should_commit()) { 831 post_self_revocation_event(&event, obj->klass()); 832 } 833 return; 834 } else { 835 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt); 836 if (cond != NOT_REVOKED) { 837 return; 838 } 839 } 840 } else { 841 assert((heuristics == HR_BULK_REVOKE) || 842 (heuristics == HR_BULK_REBIAS), "?"); 843 EventBiasedLockClassRevocation event; 844 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD, 845 (heuristics == HR_BULK_REBIAS)); 846 VMThread::execute(&bulk_revoke); 847 if (event.should_commit()) { 848 post_class_revocation_event(&event, obj->klass(), &bulk_revoke); 849 } 850 return; 851 } 852 } 853 } 854 855 // All objects in objs should be locked by biaser 856 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) { 857 bool clean_my_cache = false; 858 for (int i = 0; i < objs->length(); i++) { 859 oop obj = (objs->at(i))(); 860 markWord mark = obj->mark(); 861 if (mark.has_bias_pattern()) { 862 walk_stack_and_revoke(obj, biaser); 863 clean_my_cache = true; 864 } 865 } 866 if (clean_my_cache) { 867 clean_up_cached_monitor_info(biaser); 868 } 869 } 870 871 872 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 873 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 874 oop obj = h_obj(); 875 HeuristicsResult heuristics = update_heuristics(obj); 876 if (heuristics == HR_SINGLE_REVOKE) { 877 JavaThread* biased_locker = NULL; 878 single_revoke_at_safepoint(obj, false, NULL, &biased_locker); 879 if (biased_locker) { 880 clean_up_cached_monitor_info(biased_locker); 881 } 882 } else if ((heuristics == HR_BULK_REBIAS) || 883 (heuristics == HR_BULK_REVOKE)) { 884 bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL); 885 clean_up_cached_monitor_info(); 886 } 887 } 888 889 890 void BiasedLocking::preserve_marks() { 891 if (!UseBiasedLocking) 892 return; 893 894 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 895 896 assert(_preserved_oop_stack == NULL, "double initialization"); 897 assert(_preserved_mark_stack == NULL, "double initialization"); 898 899 // In order to reduce the number of mark words preserved during GC 900 // due to the presence of biased locking, we reinitialize most mark 901 // words to the class's prototype during GC -- even those which have 902 // a currently valid bias owner. One important situation where we 903 // must not clobber a bias is when a biased object is currently 904 // locked. To handle this case we iterate over the currently-locked 905 // monitors in a prepass and, if they are biased, preserve their 906 // mark words here. This should be a relatively small set of objects 907 // especially compared to the number of objects in the heap. 908 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true); 909 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 910 911 ResourceMark rm; 912 Thread* cur = Thread::current(); 913 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) { 914 if (thread->has_last_Java_frame()) { 915 RegisterMap rm(thread); 916 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 917 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 918 if (monitors != NULL) { 919 int len = monitors->length(); 920 // Walk monitors youngest to oldest 921 for (int i = len - 1; i >= 0; i--) { 922 MonitorInfo* mon_info = monitors->at(i); 923 if (mon_info->owner_is_scalar_replaced()) continue; 924 oop owner = mon_info->owner(); 925 if (owner != NULL) { 926 markWord mark = owner->mark(); 927 if (mark.has_bias_pattern()) { 928 _preserved_oop_stack->push(Handle(cur, owner)); 929 _preserved_mark_stack->push(mark); 930 } 931 } 932 } 933 } 934 } 935 } 936 } 937 } 938 939 940 void BiasedLocking::restore_marks() { 941 if (!UseBiasedLocking) 942 return; 943 944 assert(_preserved_oop_stack != NULL, "double free"); 945 assert(_preserved_mark_stack != NULL, "double free"); 946 947 int len = _preserved_oop_stack->length(); 948 for (int i = 0; i < len; i++) { 949 Handle owner = _preserved_oop_stack->at(i); 950 markWord mark = _preserved_mark_stack->at(i); 951 owner->set_mark(mark); 952 } 953 954 delete _preserved_oop_stack; 955 _preserved_oop_stack = NULL; 956 delete _preserved_mark_stack; 957 _preserved_mark_stack = NULL; 958 } 959 960 961 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 962 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 963 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 964 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 965 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 966 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); } 967 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 968 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 969 970 971 // BiasedLockingCounters 972 973 int BiasedLockingCounters::slow_path_entry_count() const { 974 if (_slow_path_entry_count != 0) { 975 return _slow_path_entry_count; 976 } 977 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 978 _rebiased_lock_entry_count + _revoked_lock_entry_count + 979 _fast_path_entry_count; 980 981 return _total_entry_count - sum; 982 } 983 984 void BiasedLockingCounters::print_on(outputStream* st) const { 985 tty->print_cr("# total entries: %d", _total_entry_count); 986 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 987 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 988 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 989 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 990 tty->print_cr("# handshakes entries: %d", _handshakes_count); 991 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 992 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 993 } 994 995 void BiasedLockingCounters::print() const { print_on(tty); }