rev 57156 : imported patch 8234796-v3
1 /* 2 * Copyright (c) 2005, 2019, 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/task.hpp" 39 #include "runtime/threadSMR.hpp" 40 #include "runtime/vframe.hpp" 41 #include "runtime/vmThread.hpp" 42 #include "runtime/vmOperations.hpp" 43 44 45 static bool _biased_locking_enabled = false; 46 BiasedLockingCounters BiasedLocking::_counters; 47 48 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 49 static GrowableArray<markWord>* _preserved_mark_stack = NULL; 50 51 static void enable_biased_locking(InstanceKlass* k) { 52 k->set_prototype_header(markWord::biased_locking_prototype()); 53 } 54 55 static void enable_biased_locking() { 56 _biased_locking_enabled = true; 57 log_info(biasedlocking)("Biased locking enabled"); 58 } 59 60 class VM_EnableBiasedLocking: public VM_Operation { 61 public: 62 VM_EnableBiasedLocking() {} 63 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 64 65 void doit() { 66 // Iterate the class loader data dictionaries enabling biased locking for all 67 // currently loaded classes. 68 ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking); 69 // Indicate that future instances should enable it as well 70 enable_biased_locking(); 71 } 72 73 bool allow_nested_vm_operations() const { return false; } 74 }; 75 76 77 // One-shot PeriodicTask subclass for enabling biased locking 78 class EnableBiasedLockingTask : public PeriodicTask { 79 public: 80 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 81 82 virtual void task() { 83 VM_EnableBiasedLocking op; 84 VMThread::execute(&op); 85 86 // Reclaim our storage and disenroll ourself 87 delete this; 88 } 89 }; 90 91 92 void BiasedLocking::init() { 93 // If biased locking is enabled and BiasedLockingStartupDelay is set, 94 // schedule a task to fire after the specified delay which turns on 95 // biased locking for all currently loaded classes as well as future 96 // ones. This could be a workaround for startup time regressions 97 // due to large number of safepoints being taken during VM startup for 98 // bias revocation. 99 if (UseBiasedLocking) { 100 if (BiasedLockingStartupDelay > 0) { 101 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 102 task->enroll(); 103 } else { 104 enable_biased_locking(); 105 } 106 } 107 } 108 109 110 bool BiasedLocking::enabled() { 111 assert(UseBiasedLocking, "precondition"); 112 // We check "BiasedLockingStartupDelay == 0" here to cover the 113 // possibility of calls to BiasedLocking::enabled() before 114 // BiasedLocking::init(). 115 return _biased_locking_enabled || BiasedLockingStartupDelay == 0; 116 } 117 118 119 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 120 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 121 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 122 if (info != NULL) { 123 return info; 124 } 125 126 info = new GrowableArray<MonitorInfo*>(); 127 128 // It's possible for the thread to not have any Java frames on it, 129 // i.e., if it's the main thread and it's already returned from main() 130 if (thread->has_last_Java_frame()) { 131 RegisterMap rm(thread); 132 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 133 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 134 if (monitors != NULL) { 135 int len = monitors->length(); 136 // Walk monitors youngest to oldest 137 for (int i = len - 1; i >= 0; i--) { 138 MonitorInfo* mon_info = monitors->at(i); 139 if (mon_info->eliminated()) continue; 140 oop owner = mon_info->owner(); 141 if (owner != NULL) { 142 info->append(mon_info); 143 } 144 } 145 } 146 } 147 } 148 149 thread->set_cached_monitor_info(info); 150 return info; 151 } 152 153 154 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL, 155 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization). 156 void BiasedLocking::single_revoke_at_safepoint(oop obj, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { 157 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 158 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 159 160 markWord mark = obj->mark(); 161 if (!mark.has_bias_pattern()) { 162 if (log_is_enabled(Info, biasedlocking)) { 163 ResourceMark rm; 164 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT 165 ", mark " INTPTR_FORMAT ", type %s" 166 ", requesting thread " INTPTR_FORMAT 167 " because it's no longer biased)", 168 p2i((void *)obj), mark.value(), 169 obj->klass()->external_name(), 170 (intptr_t) requesting_thread); 171 } 172 return; 173 } 174 175 uint age = mark.age(); 176 markWord unbiased_prototype = markWord::prototype().set_age(age); 177 178 // Log at "info" level if not bulk, else "trace" level 179 if (!is_bulk) { 180 ResourceMark rm; 181 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark " 182 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 183 ", requesting thread " INTPTR_FORMAT, 184 p2i((void *)obj), 185 mark.value(), 186 obj->klass()->external_name(), 187 obj->klass()->prototype_header().value(), 188 (intptr_t) requesting_thread); 189 } else { 190 ResourceMark rm; 191 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark " 192 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT 193 " , requesting thread " INTPTR_FORMAT, 194 p2i((void *)obj), 195 mark.value(), 196 obj->klass()->external_name(), 197 obj->klass()->prototype_header().value(), 198 (intptr_t) requesting_thread); 199 } 200 201 JavaThread* biased_thread = mark.biased_locker(); 202 if (biased_thread == NULL) { 203 // Object is anonymously biased. We can get here if, for 204 // example, we revoke the bias due to an identity hash code 205 // being computed for an object. 206 obj->set_mark(unbiased_prototype); 207 208 // Log at "info" level if not bulk, else "trace" level 209 if (!is_bulk) { 210 log_info(biasedlocking)(" Revoked bias of anonymously-biased object"); 211 } else { 212 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object"); 213 } 214 return; 215 } 216 217 // Handle case where the thread toward which the object was biased has exited 218 bool thread_is_alive = false; 219 if (requesting_thread == biased_thread) { 220 thread_is_alive = true; 221 } else { 222 ThreadsListHandle tlh; 223 thread_is_alive = tlh.includes(biased_thread); 224 } 225 if (!thread_is_alive) { 226 obj->set_mark(unbiased_prototype); 227 // Log at "info" level if not bulk, else "trace" level 228 if (!is_bulk) { 229 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread (" 230 PTR_FORMAT ")", p2i(biased_thread)); 231 } else { 232 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread (" 233 PTR_FORMAT ")", p2i(biased_thread)); 234 } 235 return; 236 } 237 238 // Log at "info" level if not bulk, else "trace" level 239 if (!is_bulk) { 240 log_info(biasedlocking)(" Revoked bias of object biased toward live thread (" 241 PTR_FORMAT ")", p2i(biased_thread)); 242 } else { 243 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread (" 244 PTR_FORMAT ")", p2i(biased_thread)); 245 } 246 247 // Thread owning bias is alive. 248 // Check to see whether it currently owns the lock and, if so, 249 // write down the needed displaced headers to the thread's stack. 250 // Otherwise, restore the object's header either to the unlocked 251 // or unbiased state. 252 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 253 BasicLock* highest_lock = NULL; 254 for (int i = 0; i < cached_monitor_info->length(); i++) { 255 MonitorInfo* mon_info = cached_monitor_info->at(i); 256 if (mon_info->owner() == obj) { 257 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 258 p2i((void *) mon_info->owner()), 259 p2i((void *) obj)); 260 // Assume recursive case and fix up highest lock below 261 markWord mark = markWord::encode((BasicLock*) NULL); 262 highest_lock = mon_info->lock(); 263 highest_lock->set_displaced_header(mark); 264 } else { 265 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 266 p2i((void *) mon_info->owner()), 267 p2i((void *) obj)); 268 } 269 } 270 if (highest_lock != NULL) { 271 // Fix up highest lock to contain displaced header and point 272 // object at it 273 highest_lock->set_displaced_header(unbiased_prototype); 274 // Reset object header to point to displaced mark. 275 // Must release store the lock address for platforms without TSO 276 // ordering (e.g. ppc). 277 obj->release_set_mark(markWord::encode(highest_lock)); 278 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 279 // Log at "info" level if not bulk, else "trace" level 280 if (!is_bulk) { 281 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 282 } else { 283 log_trace(biasedlocking)(" Revoked bias of currently-locked object"); 284 } 285 } else { 286 // Log at "info" level if not bulk, else "trace" level 287 if (!is_bulk) { 288 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 289 } else { 290 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object"); 291 } 292 // Store the unlocked value into the object's header. 293 obj->set_mark(unbiased_prototype); 294 } 295 296 // If requested, return information on which thread held the bias 297 if (biased_locker != NULL) { 298 *biased_locker = biased_thread; 299 } 300 } 301 302 303 enum HeuristicsResult { 304 HR_NOT_BIASED = 1, 305 HR_SINGLE_REVOKE = 2, 306 HR_BULK_REBIAS = 3, 307 HR_BULK_REVOKE = 4 308 }; 309 310 311 static HeuristicsResult update_heuristics(oop o) { 312 markWord mark = o->mark(); 313 if (!mark.has_bias_pattern()) { 314 return HR_NOT_BIASED; 315 } 316 317 // Heuristics to attempt to throttle the number of revocations. 318 // Stages: 319 // 1. Revoke the biases of all objects in the heap of this type, 320 // but allow rebiasing of those objects if unlocked. 321 // 2. Revoke the biases of all objects in the heap of this type 322 // and don't allow rebiasing of these objects. Disable 323 // allocation of objects of that type with the bias bit set. 324 Klass* k = o->klass(); 325 jlong cur_time = os::javaTimeMillis(); 326 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 327 int revocation_count = k->biased_lock_revocation_count(); 328 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 329 (revocation_count < BiasedLockingBulkRevokeThreshold) && 330 (last_bulk_revocation_time != 0) && 331 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 332 // This is the first revocation we've seen in a while of an 333 // object of this type since the last time we performed a bulk 334 // rebiasing operation. The application is allocating objects in 335 // bulk which are biased toward a thread and then handing them 336 // off to another thread. We can cope with this allocation 337 // pattern via the bulk rebiasing mechanism so we reset the 338 // klass's revocation count rather than allow it to increase 339 // monotonically. If we see the need to perform another bulk 340 // rebias operation later, we will, and if subsequently we see 341 // many more revocation operations in a short period of time we 342 // will completely disable biasing for this type. 343 k->set_biased_lock_revocation_count(0); 344 revocation_count = 0; 345 } 346 347 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 348 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 349 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 350 } 351 352 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 353 return HR_BULK_REVOKE; 354 } 355 356 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 357 return HR_BULK_REBIAS; 358 } 359 360 return HR_SINGLE_REVOKE; 361 } 362 363 364 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) { 365 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 366 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 367 368 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object " 369 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 370 (bulk_rebias ? "rebias" : "revoke"), 371 p2i((void *) o), 372 o->mark().value(), 373 o->klass()->external_name()); 374 375 jlong cur_time = os::javaTimeMillis(); 376 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 377 378 Klass* k_o = o->klass(); 379 Klass* klass = k_o; 380 381 { 382 JavaThreadIteratorWithHandle jtiwh; 383 384 if (bulk_rebias) { 385 // Use the epoch in the klass of the object to implicitly revoke 386 // all biases of objects of this data type and force them to be 387 // reacquired. However, we also need to walk the stacks of all 388 // threads and update the headers of lightweight locked objects 389 // with biases to have the current epoch. 390 391 // If the prototype header doesn't have the bias pattern, don't 392 // try to update the epoch -- assume another VM operation came in 393 // and reset the header to the unbiased state, which will 394 // implicitly cause all existing biases to be revoked 395 if (klass->prototype_header().has_bias_pattern()) { 396 int prev_epoch = klass->prototype_header().bias_epoch(); 397 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch()); 398 int cur_epoch = klass->prototype_header().bias_epoch(); 399 400 // Now walk all threads' stacks and adjust epochs of any biased 401 // and locked objects of this data type we encounter 402 for (; JavaThread *thr = jtiwh.next(); ) { 403 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 404 for (int i = 0; i < cached_monitor_info->length(); i++) { 405 MonitorInfo* mon_info = cached_monitor_info->at(i); 406 oop owner = mon_info->owner(); 407 markWord mark = owner->mark(); 408 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 409 // We might have encountered this object already in the case of recursive locking 410 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 411 owner->set_mark(mark.set_bias_epoch(cur_epoch)); 412 } 413 } 414 } 415 } 416 417 // At this point we're done. All we have to do is potentially 418 // adjust the header of the given object to revoke its bias. 419 single_revoke_at_safepoint(o, true, requesting_thread, NULL); 420 } else { 421 if (log_is_enabled(Info, biasedlocking)) { 422 ResourceMark rm; 423 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name()); 424 } 425 426 // Disable biased locking for this data type. Not only will this 427 // cause future instances to not be biased, but existing biased 428 // instances will notice that this implicitly caused their biases 429 // to be revoked. 430 klass->set_prototype_header(markWord::prototype()); 431 432 // Now walk all threads' stacks and forcibly revoke the biases of 433 // any locked and biased objects of this data type we encounter. 434 for (; JavaThread *thr = jtiwh.next(); ) { 435 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 436 for (int i = 0; i < cached_monitor_info->length(); i++) { 437 MonitorInfo* mon_info = cached_monitor_info->at(i); 438 oop owner = mon_info->owner(); 439 markWord mark = owner->mark(); 440 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 441 single_revoke_at_safepoint(owner, true, requesting_thread, NULL); 442 } 443 } 444 } 445 446 // Must force the bias of the passed object to be forcibly revoked 447 // as well to ensure guarantees to callers 448 single_revoke_at_safepoint(o, true, requesting_thread, NULL); 449 } 450 } // ThreadsListHandle is destroyed here. 451 452 log_info(biasedlocking)("* Ending bulk revocation"); 453 454 assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation"); 455 } 456 457 458 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) { 459 if (thread != NULL) { 460 thread->set_cached_monitor_info(NULL); 461 } else { 462 // Walk the thread list clearing out the cached monitors 463 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 464 thr->set_cached_monitor_info(NULL); 465 } 466 } 467 } 468 469 470 class VM_BulkRevokeBias : public VM_Operation { 471 private: 472 Handle* _obj; 473 JavaThread* _requesting_thread; 474 bool _bulk_rebias; 475 uint64_t _safepoint_id; 476 477 public: 478 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 479 bool bulk_rebias) 480 : _obj(obj) 481 , _requesting_thread(requesting_thread) 482 , _bulk_rebias(bulk_rebias) 483 , _safepoint_id(0) {} 484 485 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 486 487 virtual void doit() { 488 BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread); 489 _safepoint_id = SafepointSynchronize::safepoint_id(); 490 clean_up_cached_monitor_info(); 491 } 492 493 bool is_bulk_rebias() const { 494 return _bulk_rebias; 495 } 496 497 uint64_t safepoint_id() const { 498 return _safepoint_id; 499 } 500 }; 501 502 503 class RevokeOneBias : public ThreadClosure { 504 protected: 505 Handle _obj; 506 JavaThread* _requesting_thread; 507 JavaThread* _biased_locker; 508 BiasedLocking::Condition _status_code; 509 traceid _biased_locker_id; 510 511 public: 512 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker) 513 : _obj(obj) 514 , _requesting_thread(requesting_thread) 515 , _biased_locker(biased_locker) 516 , _status_code(BiasedLocking::NOT_BIASED) 517 , _biased_locker_id(0) {} 518 519 void do_thread(Thread* target) { 520 assert(target == _biased_locker, "Wrong thread"); 521 522 oop o = _obj(); 523 markWord mark = o->mark(); 524 525 if (!mark.has_bias_pattern()) { 526 return; 527 } 528 529 markWord prototype = o->klass()->prototype_header(); 530 if (!prototype.has_bias_pattern()) { 531 // This object has a stale bias from before the handshake 532 // was requested. If we fail this race, the object's bias 533 // has been revoked by another thread so we simply return. 534 markWord biased_value = mark; 535 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 536 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 537 if (biased_value == mark) { 538 _status_code = BiasedLocking::BIAS_REVOKED; 539 } 540 return; 541 } 542 543 if (_biased_locker == mark.biased_locker()) { 544 if (mark.bias_epoch() == prototype.bias_epoch()) { 545 // Epoch is still valid. This means biaser could be currently 546 // synchronized on this object. We must walk its stack looking 547 // for monitor records associated with this object and change 548 // them to be stack locks if any are found. 549 ResourceMark rm; 550 BiasedLocking::walk_stack_and_revoke(o, _biased_locker); 551 _biased_locker->set_cached_monitor_info(NULL); 552 assert(!o->mark().has_bias_pattern(), "invariant"); 553 _biased_locker_id = JFR_THREAD_ID(_biased_locker); 554 _status_code = BiasedLocking::BIAS_REVOKED; 555 return; 556 } else { 557 markWord biased_value = mark; 558 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 559 if (mark == biased_value || !mark.has_bias_pattern()) { 560 assert(!o->mark().has_bias_pattern(), "should be revoked"); 561 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED; 562 return; 563 } 564 } 565 } 566 567 _status_code = BiasedLocking::NOT_REVOKED; 568 } 569 570 BiasedLocking::Condition status_code() const { 571 return _status_code; 572 } 573 574 traceid biased_locker() const { 575 return _biased_locker_id; 576 } 577 }; 578 579 580 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) { 581 assert(event != NULL, "invariant"); 582 assert(k != NULL, "invariant"); 583 assert(event->should_commit(), "invariant"); 584 event->set_lockClass(k); 585 event->commit(); 586 } 587 588 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) { 589 assert(event != NULL, "invariant"); 590 assert(k != NULL, "invariant"); 591 assert(op != NULL, "invariant"); 592 assert(event->should_commit(), "invariant"); 593 event->set_lockClass(k); 594 event->set_safepointId(0); 595 event->set_previousOwner(op->biased_locker()); 596 event->commit(); 597 } 598 599 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) { 600 assert(event != NULL, "invariant"); 601 assert(k != NULL, "invariant"); 602 assert(op != NULL, "invariant"); 603 assert(event->should_commit(), "invariant"); 604 event->set_revokedClass(k); 605 event->set_disableBiasing(!op->is_bulk_rebias()); 606 event->set_safepointId(op->safepoint_id()); 607 event->commit(); 608 } 609 610 611 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) { 612 613 EventBiasedLockRevocation event; 614 if (PrintBiasedLockingStatistics) { 615 Atomic::inc(handshakes_count_addr()); 616 } 617 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread " 618 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester), 619 p2i(biaser), p2i(obj())); 620 621 RevokeOneBias revoke(obj, requester, biaser); 622 bool executed = Handshake::execute(&revoke, biaser); 623 if (revoke.status_code() == NOT_REVOKED) { 624 return NOT_REVOKED; 625 } 626 if (executed) { 627 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked", 628 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already ")); 629 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) { 630 post_revocation_event(&event, obj->klass(), &revoke); 631 } 632 assert(!obj->mark().has_bias_pattern(), "invariant"); 633 return revoke.status_code(); 634 } else { 635 // Thread was not alive. 636 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly 637 // created JavaThread (that happens to get the same memory address as biaser) synchronizing 638 // on this object. 639 { 640 MutexLocker ml(Threads_lock); 641 markWord mark = obj->mark(); 642 // Check if somebody else was able to revoke it before biased thread exited. 643 if (!mark.has_bias_pattern()) { 644 return NOT_BIASED; 645 } 646 ThreadsListHandle tlh; 647 markWord prototype = obj->klass()->prototype_header(); 648 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() && 649 prototype.bias_epoch() == mark.bias_epoch())) { 650 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 651 if (event.should_commit()) { 652 post_revocation_event(&event, obj->klass(), &revoke); 653 } 654 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now"); 655 return BIAS_REVOKED; 656 } 657 } 658 } 659 660 return NOT_REVOKED; 661 } 662 663 664 // Caller should have instantiated a ResourceMark object before calling this method 665 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) { 666 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes, 667 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints"); 668 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread"); 669 670 markWord mark = obj->mark(); 671 assert(mark.biased_locker() == biased_locker && 672 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant"); 673 674 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark " 675 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 676 ", biaser " INTPTR_FORMAT " %s", 677 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread", 678 p2i(Thread::current()), 679 p2i(obj), 680 mark.value(), 681 obj->klass()->external_name(), 682 obj->klass()->prototype_header().value(), 683 p2i(biased_locker), 684 Thread::current()->is_VM_thread() ? "" : "(walking own stack)"); 685 686 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age()); 687 688 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker); 689 BasicLock* highest_lock = NULL; 690 for (int i = 0; i < cached_monitor_info->length(); i++) { 691 MonitorInfo* mon_info = cached_monitor_info->at(i); 692 if (mon_info->owner() == obj) { 693 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 694 p2i(mon_info->owner()), 695 p2i(obj)); 696 // Assume recursive case and fix up highest lock below 697 markWord mark = markWord::encode((BasicLock*) NULL); 698 highest_lock = mon_info->lock(); 699 highest_lock->set_displaced_header(mark); 700 } else { 701 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 702 p2i(mon_info->owner()), 703 p2i(obj)); 704 } 705 } 706 if (highest_lock != NULL) { 707 // Fix up highest lock to contain displaced header and point 708 // object at it 709 highest_lock->set_displaced_header(unbiased_prototype); 710 // Reset object header to point to displaced mark. 711 // Must release store the lock address for platforms without TSO 712 // ordering (e.g. ppc). 713 obj->release_set_mark(markWord::encode(highest_lock)); 714 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 715 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 716 } else { 717 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 718 // Store the unlocked value into the object's header. 719 obj->set_mark(unbiased_prototype); 720 } 721 722 assert(!obj->mark().has_bias_pattern(), "must not be biased"); 723 } 724 725 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) { 726 assert(THREAD->is_Java_thread(), "must be called by a JavaThread"); 727 JavaThread* thread = (JavaThread*)THREAD; 728 729 markWord mark = obj->mark(); 730 731 if (!mark.has_bias_pattern()) { 732 return; 733 } 734 735 Klass *k = obj->klass(); 736 assert(mark.biased_locker() == thread && 737 k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state"); 738 ResourceMark rm; 739 log_info(biasedlocking)("Revoking bias by walking my own stack:"); 740 EventBiasedLockSelfRevocation event; 741 BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread); 742 thread->set_cached_monitor_info(NULL); 743 assert(!obj->mark().has_bias_pattern(), "invariant"); 744 if (event.should_commit()) { 745 post_self_revocation_event(&event, k); 746 } 747 } 748 749 void BiasedLocking::revoke(Handle obj, TRAPS) { 750 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 751 752 while (true) { 753 // We can revoke the biases of anonymously-biased objects 754 // efficiently enough that we should not cause these revocations to 755 // update the heuristics because doing so may cause unwanted bulk 756 // revocations (which are expensive) to occur. 757 markWord mark = obj->mark(); 758 759 if (!mark.has_bias_pattern()) { 760 return; 761 } 762 763 if (mark.is_biased_anonymously()) { 764 // We are probably trying to revoke the bias of this object due to 765 // an identity hash code computation. Try to revoke the bias 766 // without a safepoint. This is possible if we can successfully 767 // compare-and-exchange an unbiased header into the mark word of 768 // the object, meaning that no other thread has raced to acquire 769 // the bias of the object. 770 markWord biased_value = mark; 771 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 772 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark); 773 if (res_mark == biased_value) { 774 return; 775 } 776 mark = res_mark; // Refresh mark with the latest value. 777 } else { 778 Klass* k = obj->klass(); 779 markWord prototype_header = k->prototype_header(); 780 if (!prototype_header.has_bias_pattern()) { 781 // This object has a stale bias from before the bulk revocation 782 // for this data type occurred. It's pointless to update the 783 // heuristics at this point so simply update the header with a 784 // CAS. If we fail this race, the object's bias has been revoked 785 // by another thread so we simply return and let the caller deal 786 // with it. 787 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark); 788 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 789 return; 790 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) { 791 // The epoch of this biasing has expired indicating that the 792 // object is effectively unbiased. We can revoke the bias of this 793 // object efficiently enough with a CAS that we shouldn't update the 794 // heuristics. This is normally done in the assembly code but we 795 // can reach this point due to various points in the runtime 796 // needing to revoke biases. 797 markWord res_mark; 798 markWord biased_value = mark; 799 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 800 res_mark = obj->cas_set_mark(unbiased_prototype, mark); 801 if (res_mark == biased_value) { 802 return; 803 } 804 mark = res_mark; // Refresh mark with the latest value. 805 } 806 } 807 808 HeuristicsResult heuristics = update_heuristics(obj()); 809 if (heuristics == HR_NOT_BIASED) { 810 return; 811 } else if (heuristics == HR_SINGLE_REVOKE) { 812 JavaThread *blt = mark.biased_locker(); 813 assert(blt != NULL, "invariant"); 814 if (blt == THREAD) { 815 // A thread is trying to revoke the bias of an object biased 816 // toward it, again likely due to an identity hash code 817 // computation. We can again avoid a safepoint/handshake in this case 818 // since we are only going to walk our own stack. There are no 819 // races with revocations occurring in other threads because we 820 // reach no safepoints in the revocation path. 821 EventBiasedLockSelfRevocation event; 822 ResourceMark rm; 823 walk_stack_and_revoke(obj(), blt); 824 blt->set_cached_monitor_info(NULL); 825 assert(!obj->mark().has_bias_pattern(), "invariant"); 826 if (event.should_commit()) { 827 post_self_revocation_event(&event, obj->klass()); 828 } 829 return; 830 } else { 831 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt); 832 if (cond != NOT_REVOKED) { 833 return; 834 } 835 } 836 } else { 837 assert((heuristics == HR_BULK_REVOKE) || 838 (heuristics == HR_BULK_REBIAS), "?"); 839 EventBiasedLockClassRevocation event; 840 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD, 841 (heuristics == HR_BULK_REBIAS)); 842 VMThread::execute(&bulk_revoke); 843 if (event.should_commit()) { 844 post_class_revocation_event(&event, obj->klass(), &bulk_revoke); 845 } 846 return; 847 } 848 } 849 } 850 851 // All objects in objs should be locked by biaser 852 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) { 853 bool clean_my_cache = false; 854 for (int i = 0; i < objs->length(); i++) { 855 oop obj = (objs->at(i))(); 856 markWord mark = obj->mark(); 857 if (mark.has_bias_pattern()) { 858 walk_stack_and_revoke(obj, biaser); 859 clean_my_cache = true; 860 } 861 } 862 if (clean_my_cache) { 863 clean_up_cached_monitor_info(biaser); 864 } 865 } 866 867 868 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 869 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 870 oop obj = h_obj(); 871 HeuristicsResult heuristics = update_heuristics(obj); 872 if (heuristics == HR_SINGLE_REVOKE) { 873 JavaThread* biased_locker = NULL; 874 single_revoke_at_safepoint(obj, false, NULL, &biased_locker); 875 if (biased_locker) { 876 clean_up_cached_monitor_info(biased_locker); 877 } 878 } else if ((heuristics == HR_BULK_REBIAS) || 879 (heuristics == HR_BULK_REVOKE)) { 880 bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL); 881 clean_up_cached_monitor_info(); 882 } 883 } 884 885 886 void BiasedLocking::preserve_marks() { 887 if (!UseBiasedLocking) 888 return; 889 890 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 891 892 assert(_preserved_oop_stack == NULL, "double initialization"); 893 assert(_preserved_mark_stack == NULL, "double initialization"); 894 895 // In order to reduce the number of mark words preserved during GC 896 // due to the presence of biased locking, we reinitialize most mark 897 // words to the class's prototype during GC -- even those which have 898 // a currently valid bias owner. One important situation where we 899 // must not clobber a bias is when a biased object is currently 900 // locked. To handle this case we iterate over the currently-locked 901 // monitors in a prepass and, if they are biased, preserve their 902 // mark words here. This should be a relatively small set of objects 903 // especially compared to the number of objects in the heap. 904 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true); 905 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 906 907 ResourceMark rm; 908 Thread* cur = Thread::current(); 909 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) { 910 if (thread->has_last_Java_frame()) { 911 RegisterMap rm(thread); 912 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 913 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 914 if (monitors != NULL) { 915 int len = monitors->length(); 916 // Walk monitors youngest to oldest 917 for (int i = len - 1; i >= 0; i--) { 918 MonitorInfo* mon_info = monitors->at(i); 919 if (mon_info->owner_is_scalar_replaced()) continue; 920 oop owner = mon_info->owner(); 921 if (owner != NULL) { 922 markWord mark = owner->mark(); 923 if (mark.has_bias_pattern()) { 924 _preserved_oop_stack->push(Handle(cur, owner)); 925 _preserved_mark_stack->push(mark); 926 } 927 } 928 } 929 } 930 } 931 } 932 } 933 } 934 935 936 void BiasedLocking::restore_marks() { 937 if (!UseBiasedLocking) 938 return; 939 940 assert(_preserved_oop_stack != NULL, "double free"); 941 assert(_preserved_mark_stack != NULL, "double free"); 942 943 int len = _preserved_oop_stack->length(); 944 for (int i = 0; i < len; i++) { 945 Handle owner = _preserved_oop_stack->at(i); 946 markWord mark = _preserved_mark_stack->at(i); 947 owner->set_mark(mark); 948 } 949 950 delete _preserved_oop_stack; 951 _preserved_oop_stack = NULL; 952 delete _preserved_mark_stack; 953 _preserved_mark_stack = NULL; 954 } 955 956 957 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 958 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 959 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 960 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 961 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 962 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); } 963 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 964 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 965 966 967 // BiasedLockingCounters 968 969 int BiasedLockingCounters::slow_path_entry_count() const { 970 if (_slow_path_entry_count != 0) { 971 return _slow_path_entry_count; 972 } 973 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 974 _rebiased_lock_entry_count + _revoked_lock_entry_count + 975 _fast_path_entry_count; 976 977 return _total_entry_count - sum; 978 } 979 980 void BiasedLockingCounters::print_on(outputStream* st) const { 981 tty->print_cr("# total entries: %d", _total_entry_count); 982 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 983 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 984 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 985 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 986 tty->print_cr("# handshakes entries: %d", _handshakes_count); 987 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 988 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 989 } 990 991 void BiasedLockingCounters::print() const { print_on(tty); } --- EOF ---