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 Mode evaluation_mode() const { return _async_safepoint; } 65 bool is_cheap_allocated() const { return true; } 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 // Use async VM operation to avoid blocking the Watcher thread. 86 // VM Thread will free C heap storage. 87 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(); 88 VMThread::execute(op); 89 90 // Reclaim our storage and disenroll ourself 91 delete this; 92 } 93 }; 94 95 96 void BiasedLocking::init() { 97 // If biased locking is enabled and BiasedLockingStartupDelay is set, 98 // schedule a task to fire after the specified delay which turns on 99 // biased locking for all currently loaded classes as well as future 100 // ones. This could be a workaround for startup time regressions 101 // due to large number of safepoints being taken during VM startup for 102 // bias revocation. 103 if (UseBiasedLocking) { 104 if (BiasedLockingStartupDelay > 0) { 105 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 106 task->enroll(); 107 } else { 108 enable_biased_locking(); 109 } 110 } 111 } 112 113 114 bool BiasedLocking::enabled() { 115 assert(UseBiasedLocking, "precondition"); 116 // We check "BiasedLockingStartupDelay == 0" here to cover the 117 // possibility of calls to BiasedLocking::enabled() before 118 // BiasedLocking::init(). 119 return _biased_locking_enabled || BiasedLockingStartupDelay == 0; 120 } 121 122 123 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 124 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 125 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 126 if (info != NULL) { 127 return info; 128 } 129 130 info = new GrowableArray<MonitorInfo*>(); 131 132 // It's possible for the thread to not have any Java frames on it, 133 // i.e., if it's the main thread and it's already returned from main() 134 if (thread->has_last_Java_frame()) { 135 RegisterMap rm(thread); 136 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 137 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 138 if (monitors != NULL) { 139 int len = monitors->length(); 140 // Walk monitors youngest to oldest 141 for (int i = len - 1; i >= 0; i--) { 142 MonitorInfo* mon_info = monitors->at(i); 143 if (mon_info->eliminated()) continue; 144 oop owner = mon_info->owner(); 145 if (owner != NULL) { 146 info->append(mon_info); 147 } 148 } 149 } 150 } 151 } 152 153 thread->set_cached_monitor_info(info); 154 return info; 155 } 156 157 158 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL, 159 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization). 160 BiasedLocking::Condition BiasedLocking::single_revoke_at_safepoint(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) { 161 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 162 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 163 164 markWord mark = obj->mark(); 165 if (!mark.has_bias_pattern()) { 166 if (log_is_enabled(Info, biasedlocking)) { 167 ResourceMark rm; 168 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT 169 ", mark " INTPTR_FORMAT ", type %s" 170 ", requesting thread " INTPTR_FORMAT 171 " because it's no longer biased)", 172 p2i((void *)obj), mark.value(), 173 obj->klass()->external_name(), 174 (intptr_t) requesting_thread); 175 } 176 return NOT_BIASED; 177 } 178 179 uint age = mark.age(); 180 markWord biased_prototype = markWord::biased_locking_prototype().set_age(age); 181 markWord unbiased_prototype = markWord::prototype().set_age(age); 182 183 // Log at "info" level if not bulk, else "trace" level 184 if (!is_bulk) { 185 ResourceMark rm; 186 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark " 187 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 188 ", allow rebias %d, requesting thread " INTPTR_FORMAT, 189 p2i((void *)obj), 190 mark.value(), 191 obj->klass()->external_name(), 192 obj->klass()->prototype_header().value(), 193 (allow_rebias ? 1 : 0), 194 (intptr_t) requesting_thread); 195 } else { 196 ResourceMark rm; 197 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark " 198 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT 199 " , allow rebias %d , requesting thread " INTPTR_FORMAT, 200 p2i((void *)obj), 201 mark.value(), 202 obj->klass()->external_name(), 203 obj->klass()->prototype_header().value(), 204 (allow_rebias ? 1 : 0), 205 (intptr_t) requesting_thread); 206 } 207 208 JavaThread* biased_thread = mark.biased_locker(); 209 if (biased_thread == NULL) { 210 // Object is anonymously biased. We can get here if, for 211 // example, we revoke the bias due to an identity hash code 212 // being computed for an object. 213 if (!allow_rebias) { 214 obj->set_mark(unbiased_prototype); 215 } 216 // Log at "info" level if not bulk, else "trace" level 217 if (!is_bulk) { 218 log_info(biasedlocking)(" Revoked bias of anonymously-biased object"); 219 } else { 220 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object"); 221 } 222 return BIAS_REVOKED; 223 } 224 225 // Handle case where the thread toward which the object was biased has exited 226 bool thread_is_alive = false; 227 if (requesting_thread == biased_thread) { 228 thread_is_alive = true; 229 } else { 230 ThreadsListHandle tlh; 231 thread_is_alive = tlh.includes(biased_thread); 232 } 233 if (!thread_is_alive) { 234 if (allow_rebias) { 235 obj->set_mark(biased_prototype); 236 } else { 237 obj->set_mark(unbiased_prototype); 238 } 239 // Log at "info" level if not bulk, else "trace" level 240 if (!is_bulk) { 241 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread (" 242 PTR_FORMAT ")", p2i(biased_thread)); 243 } else { 244 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread (" 245 PTR_FORMAT ")", p2i(biased_thread)); 246 } 247 return BIAS_REVOKED; 248 } 249 250 // Log at "info" level if not bulk, else "trace" level 251 if (!is_bulk) { 252 log_info(biasedlocking)(" Revoked bias of object biased toward live thread (" 253 PTR_FORMAT ")", p2i(biased_thread)); 254 } else { 255 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread (" 256 PTR_FORMAT ")", p2i(biased_thread)); 257 } 258 259 // Thread owning bias is alive. 260 // Check to see whether it currently owns the lock and, if so, 261 // write down the needed displaced headers to the thread's stack. 262 // Otherwise, restore the object's header either to the unlocked 263 // or unbiased state. 264 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); 265 BasicLock* highest_lock = NULL; 266 for (int i = 0; i < cached_monitor_info->length(); i++) { 267 MonitorInfo* mon_info = cached_monitor_info->at(i); 268 if (oopDesc::equals(mon_info->owner(), obj)) { 269 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 270 p2i((void *) mon_info->owner()), 271 p2i((void *) obj)); 272 // Assume recursive case and fix up highest lock below 273 markWord mark = markWord::encode((BasicLock*) NULL); 274 highest_lock = mon_info->lock(); 275 highest_lock->set_displaced_header(mark); 276 } else { 277 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 278 p2i((void *) mon_info->owner()), 279 p2i((void *) obj)); 280 } 281 } 282 if (highest_lock != NULL) { 283 // Fix up highest lock to contain displaced header and point 284 // object at it 285 highest_lock->set_displaced_header(unbiased_prototype); 286 // Reset object header to point to displaced mark. 287 // Must release store the lock address for platforms without TSO 288 // ordering (e.g. ppc). 289 obj->release_set_mark(markWord::encode(highest_lock)); 290 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 291 // Log at "info" level if not bulk, else "trace" level 292 if (!is_bulk) { 293 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 294 } else { 295 log_trace(biasedlocking)(" Revoked bias of currently-locked object"); 296 } 297 } else { 298 // Log at "info" level if not bulk, else "trace" level 299 if (!is_bulk) { 300 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 301 } else { 302 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object"); 303 } 304 if (allow_rebias) { 305 obj->set_mark(biased_prototype); 306 } else { 307 // Store the unlocked value into the object's header. 308 obj->set_mark(unbiased_prototype); 309 } 310 } 311 312 // If requested, return information on which thread held the bias 313 if (biased_locker != NULL) { 314 *biased_locker = biased_thread; 315 } 316 317 return BIAS_REVOKED; 318 } 319 320 321 enum HeuristicsResult { 322 HR_NOT_BIASED = 1, 323 HR_SINGLE_REVOKE = 2, 324 HR_BULK_REBIAS = 3, 325 HR_BULK_REVOKE = 4 326 }; 327 328 329 static HeuristicsResult update_heuristics(oop o) { 330 markWord mark = o->mark(); 331 if (!mark.has_bias_pattern()) { 332 return HR_NOT_BIASED; 333 } 334 335 // Heuristics to attempt to throttle the number of revocations. 336 // Stages: 337 // 1. Revoke the biases of all objects in the heap of this type, 338 // but allow rebiasing of those objects if unlocked. 339 // 2. Revoke the biases of all objects in the heap of this type 340 // and don't allow rebiasing of these objects. Disable 341 // allocation of objects of that type with the bias bit set. 342 Klass* k = o->klass(); 343 jlong cur_time = os::javaTimeMillis(); 344 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 345 int revocation_count = k->biased_lock_revocation_count(); 346 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 347 (revocation_count < BiasedLockingBulkRevokeThreshold) && 348 (last_bulk_revocation_time != 0) && 349 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 350 // This is the first revocation we've seen in a while of an 351 // object of this type since the last time we performed a bulk 352 // rebiasing operation. The application is allocating objects in 353 // bulk which are biased toward a thread and then handing them 354 // off to another thread. We can cope with this allocation 355 // pattern via the bulk rebiasing mechanism so we reset the 356 // klass's revocation count rather than allow it to increase 357 // monotonically. If we see the need to perform another bulk 358 // rebias operation later, we will, and if subsequently we see 359 // many more revocation operations in a short period of time we 360 // will completely disable biasing for this type. 361 k->set_biased_lock_revocation_count(0); 362 revocation_count = 0; 363 } 364 365 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 366 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 367 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 368 } 369 370 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 371 return HR_BULK_REVOKE; 372 } 373 374 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 375 return HR_BULK_REBIAS; 376 } 377 378 return HR_SINGLE_REVOKE; 379 } 380 381 382 BiasedLocking::Condition BiasedLocking::bulk_revoke_or_rebias_at_safepoint(oop o, 383 bool bulk_rebias, 384 bool attempt_rebias_of_object, 385 JavaThread* requesting_thread) { 386 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 387 assert(Thread::current()->is_VM_thread(), "must be VMThread"); 388 389 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object " 390 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 391 (bulk_rebias ? "rebias" : "revoke"), 392 p2i((void *) o), 393 o->mark().value(), 394 o->klass()->external_name()); 395 396 jlong cur_time = os::javaTimeMillis(); 397 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 398 399 Klass* k_o = o->klass(); 400 Klass* klass = k_o; 401 402 { 403 JavaThreadIteratorWithHandle jtiwh; 404 405 if (bulk_rebias) { 406 // Use the epoch in the klass of the object to implicitly revoke 407 // all biases of objects of this data type and force them to be 408 // reacquired. However, we also need to walk the stacks of all 409 // threads and update the headers of lightweight locked objects 410 // with biases to have the current epoch. 411 412 // If the prototype header doesn't have the bias pattern, don't 413 // try to update the epoch -- assume another VM operation came in 414 // and reset the header to the unbiased state, which will 415 // implicitly cause all existing biases to be revoked 416 if (klass->prototype_header().has_bias_pattern()) { 417 int prev_epoch = klass->prototype_header().bias_epoch(); 418 klass->set_prototype_header(klass->prototype_header().incr_bias_epoch()); 419 int cur_epoch = klass->prototype_header().bias_epoch(); 420 421 // Now walk all threads' stacks and adjust epochs of any biased 422 // and locked objects of this data type we encounter 423 for (; JavaThread *thr = jtiwh.next(); ) { 424 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 425 for (int i = 0; i < cached_monitor_info->length(); i++) { 426 MonitorInfo* mon_info = cached_monitor_info->at(i); 427 oop owner = mon_info->owner(); 428 markWord mark = owner->mark(); 429 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 430 // We might have encountered this object already in the case of recursive locking 431 assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 432 owner->set_mark(mark.set_bias_epoch(cur_epoch)); 433 } 434 } 435 } 436 } 437 438 // At this point we're done. All we have to do is potentially 439 // adjust the header of the given object to revoke its bias. 440 single_revoke_at_safepoint(o, attempt_rebias_of_object && klass->prototype_header().has_bias_pattern(), true, requesting_thread, NULL); 441 } else { 442 if (log_is_enabled(Info, biasedlocking)) { 443 ResourceMark rm; 444 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name()); 445 } 446 447 // Disable biased locking for this data type. Not only will this 448 // cause future instances to not be biased, but existing biased 449 // instances will notice that this implicitly caused their biases 450 // to be revoked. 451 klass->set_prototype_header(markWord::prototype()); 452 453 // Now walk all threads' stacks and forcibly revoke the biases of 454 // any locked and biased objects of this data type we encounter. 455 for (; JavaThread *thr = jtiwh.next(); ) { 456 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 457 for (int i = 0; i < cached_monitor_info->length(); i++) { 458 MonitorInfo* mon_info = cached_monitor_info->at(i); 459 oop owner = mon_info->owner(); 460 markWord mark = owner->mark(); 461 if ((owner->klass() == k_o) && mark.has_bias_pattern()) { 462 single_revoke_at_safepoint(owner, false, true, requesting_thread, NULL); 463 } 464 } 465 } 466 467 // Must force the bias of the passed object to be forcibly revoked 468 // as well to ensure guarantees to callers 469 single_revoke_at_safepoint(o, false, true, requesting_thread, NULL); 470 } 471 } // ThreadsListHandle is destroyed here. 472 473 log_info(biasedlocking)("* Ending bulk revocation"); 474 475 BiasedLocking::Condition status_code = BIAS_REVOKED; 476 477 if (attempt_rebias_of_object && 478 o->mark().has_bias_pattern() && 479 klass->prototype_header().has_bias_pattern()) { 480 markWord new_mark = markWord::encode(requesting_thread, o->mark().age(), 481 klass->prototype_header().bias_epoch()); 482 o->set_mark(new_mark); 483 status_code = BIAS_REVOKED_AND_REBIASED; 484 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 485 } 486 487 assert(!o->mark().has_bias_pattern() || 488 (attempt_rebias_of_object && (o->mark().biased_locker() == requesting_thread)), 489 "bug in bulk bias revocation"); 490 491 return status_code; 492 } 493 494 495 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) { 496 if (thread != NULL) { 497 thread->set_cached_monitor_info(NULL); 498 } else { 499 // Walk the thread list clearing out the cached monitors 500 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) { 501 thr->set_cached_monitor_info(NULL); 502 } 503 } 504 } 505 506 507 class VM_BulkRevokeBias : public VM_Operation { 508 private: 509 Handle* _obj; 510 JavaThread* _requesting_thread; 511 bool _bulk_rebias; 512 bool _attempt_rebias_of_object; 513 BiasedLocking::Condition _status_code; 514 uint64_t _safepoint_id; 515 516 public: 517 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 518 bool bulk_rebias, 519 bool attempt_rebias_of_object) 520 : _obj(obj) 521 , _requesting_thread(requesting_thread) 522 , _bulk_rebias(bulk_rebias) 523 , _attempt_rebias_of_object(attempt_rebias_of_object) 524 , _status_code(BiasedLocking::NOT_BIASED) 525 , _safepoint_id(0) {} 526 527 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 528 529 virtual void doit() { 530 _status_code = BiasedLocking::bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 531 _safepoint_id = SafepointSynchronize::safepoint_id(); 532 clean_up_cached_monitor_info(); 533 } 534 535 bool is_bulk_rebias() const { 536 return _bulk_rebias; 537 } 538 539 BiasedLocking::Condition status_code() const { 540 return _status_code; 541 } 542 543 uint64_t safepoint_id() const { 544 return _safepoint_id; 545 } 546 }; 547 548 549 class RevokeOneBias : public ThreadClosure { 550 protected: 551 Handle _obj; 552 JavaThread* _requesting_thread; 553 JavaThread* _biased_locker; 554 BiasedLocking::Condition _status_code; 555 traceid _biased_locker_id; 556 557 public: 558 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker) 559 : _obj(obj) 560 , _requesting_thread(requesting_thread) 561 , _biased_locker(biased_locker) 562 , _status_code(BiasedLocking::NOT_BIASED) 563 , _biased_locker_id(0) {} 564 565 void do_thread(Thread* target) { 566 assert(target == _biased_locker, "Wrong thread"); 567 568 oop o = _obj(); 569 markWord mark = o->mark(); 570 571 if (!mark.has_bias_pattern()) { 572 return; 573 } 574 575 markWord prototype = o->klass()->prototype_header(); 576 if (!prototype.has_bias_pattern()) { 577 // This object has a stale bias from before the handshake 578 // was requested. If we fail this race, the object's bias 579 // has been revoked by another thread so we simply return. 580 markWord biased_value = mark; 581 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 582 assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 583 if (biased_value == mark) { 584 _status_code = BiasedLocking::BIAS_REVOKED; 585 } 586 return; 587 } 588 589 if (_biased_locker == mark.biased_locker()) { 590 if (mark.bias_epoch() == prototype.bias_epoch()) { 591 // Epoch is still valid. This means biaser could be currently 592 // synchronized on this object. We must walk its stack looking 593 // for monitor records associated with this object and change 594 // them to be stack locks if any are found. 595 ResourceMark rm; 596 BiasedLocking::walk_stack_and_revoke(o, _biased_locker); 597 _biased_locker->set_cached_monitor_info(NULL); 598 assert(!o->mark().has_bias_pattern(), "invariant"); 599 _biased_locker_id = JFR_THREAD_ID(_biased_locker); 600 _status_code = BiasedLocking::BIAS_REVOKED; 601 return; 602 } else { 603 markWord biased_value = mark; 604 mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 605 if (mark == biased_value || !mark.has_bias_pattern()) { 606 assert(!o->mark().has_bias_pattern(), "should be revoked"); 607 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED; 608 return; 609 } 610 } 611 } 612 613 _status_code = BiasedLocking::NOT_REVOKED; 614 } 615 616 BiasedLocking::Condition status_code() const { 617 return _status_code; 618 } 619 620 traceid biased_locker() const { 621 return _biased_locker_id; 622 } 623 }; 624 625 626 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) { 627 assert(event != NULL, "invariant"); 628 assert(k != NULL, "invariant"); 629 assert(event->should_commit(), "invariant"); 630 event->set_lockClass(k); 631 event->commit(); 632 } 633 634 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) { 635 assert(event != NULL, "invariant"); 636 assert(k != NULL, "invariant"); 637 assert(op != NULL, "invariant"); 638 assert(event->should_commit(), "invariant"); 639 event->set_lockClass(k); 640 event->set_safepointId(0); 641 event->set_previousOwner(op->biased_locker()); 642 event->commit(); 643 } 644 645 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) { 646 assert(event != NULL, "invariant"); 647 assert(k != NULL, "invariant"); 648 assert(op != NULL, "invariant"); 649 assert(event->should_commit(), "invariant"); 650 event->set_revokedClass(k); 651 event->set_disableBiasing(!op->is_bulk_rebias()); 652 event->set_safepointId(op->safepoint_id()); 653 event->commit(); 654 } 655 656 657 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) { 658 659 EventBiasedLockRevocation event; 660 if (PrintBiasedLockingStatistics) { 661 Atomic::inc(handshakes_count_addr()); 662 } 663 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread " 664 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester), 665 p2i(biaser), p2i(obj())); 666 667 RevokeOneBias revoke(obj, requester, biaser); 668 bool executed = Handshake::execute(&revoke, biaser); 669 if (revoke.status_code() == NOT_REVOKED) { 670 return NOT_REVOKED; 671 } 672 if (executed) { 673 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked", 674 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already ")); 675 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) { 676 post_revocation_event(&event, obj->klass(), &revoke); 677 } 678 assert(!obj->mark().has_bias_pattern(), "invariant"); 679 return revoke.status_code(); 680 } else { 681 // Thread was not alive. 682 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly 683 // created JavaThread (that happens to get the same memory address as biaser) synchronizing 684 // on this object. 685 { 686 MutexLocker ml(Threads_lock); 687 markWord mark = obj->mark(); 688 // Check if somebody else was able to revoke it before biased thread exited. 689 if (!mark.has_bias_pattern()) { 690 return NOT_BIASED; 691 } 692 ThreadsListHandle tlh; 693 markWord prototype = obj->klass()->prototype_header(); 694 if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() && 695 prototype.bias_epoch() == mark.bias_epoch())) { 696 obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark); 697 if (event.should_commit()) { 698 post_revocation_event(&event, obj->klass(), &revoke); 699 } 700 assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now"); 701 return BIAS_REVOKED; 702 } 703 } 704 } 705 706 return NOT_REVOKED; 707 } 708 709 710 // Caller should have instantiated a ResourceMark object before calling this method 711 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) { 712 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes, 713 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints"); 714 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread"); 715 716 markWord mark = obj->mark(); 717 assert(mark.biased_locker() == biased_locker && 718 obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant"); 719 720 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark " 721 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 722 ", biaser " INTPTR_FORMAT " %s", 723 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread", 724 p2i(Thread::current()), 725 p2i(obj), 726 mark.value(), 727 obj->klass()->external_name(), 728 obj->klass()->prototype_header().value(), 729 p2i(biased_locker), 730 Thread::current()->is_VM_thread() ? "" : "(walking own stack)"); 731 732 markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age()); 733 734 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker); 735 BasicLock* highest_lock = NULL; 736 for (int i = 0; i < cached_monitor_info->length(); i++) { 737 MonitorInfo* mon_info = cached_monitor_info->at(i); 738 if (oopDesc::equals(mon_info->owner(), obj)) { 739 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", 740 p2i(mon_info->owner()), 741 p2i(obj)); 742 // Assume recursive case and fix up highest lock below 743 markWord mark = markWord::encode((BasicLock*) NULL); 744 highest_lock = mon_info->lock(); 745 highest_lock->set_displaced_header(mark); 746 } else { 747 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", 748 p2i(mon_info->owner()), 749 p2i(obj)); 750 } 751 } 752 if (highest_lock != NULL) { 753 // Fix up highest lock to contain displaced header and point 754 // object at it 755 highest_lock->set_displaced_header(unbiased_prototype); 756 // Reset object header to point to displaced mark. 757 // Must release store the lock address for platforms without TSO 758 // ordering (e.g. ppc). 759 obj->release_set_mark(markWord::encode(highest_lock)); 760 assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit"); 761 log_info(biasedlocking)(" Revoked bias of currently-locked object"); 762 } else { 763 log_info(biasedlocking)(" Revoked bias of currently-unlocked object"); 764 // Store the unlocked value into the object's header. 765 obj->set_mark(unbiased_prototype); 766 } 767 768 assert(!obj->mark().has_bias_pattern(), "must not be biased"); 769 } 770 771 772 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 773 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 774 775 while (true) { 776 // We can revoke the biases of anonymously-biased objects 777 // efficiently enough that we should not cause these revocations to 778 // update the heuristics because doing so may cause unwanted bulk 779 // revocations (which are expensive) to occur. 780 markWord mark = obj->mark(); 781 if (mark.is_biased_anonymously() && !attempt_rebias) { 782 // We are probably trying to revoke the bias of this object due to 783 // an identity hash code computation. Try to revoke the bias 784 // without a safepoint. This is possible if we can successfully 785 // compare-and-exchange an unbiased header into the mark word of 786 // the object, meaning that no other thread has raced to acquire 787 // the bias of the object. 788 markWord biased_value = mark; 789 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 790 markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark); 791 if (res_mark == biased_value) { 792 return BIAS_REVOKED; 793 } 794 mark = res_mark; // Refresh mark with the latest value. 795 } else if (mark.has_bias_pattern()) { 796 Klass* k = obj->klass(); 797 markWord prototype_header = k->prototype_header(); 798 if (!prototype_header.has_bias_pattern()) { 799 // This object has a stale bias from before the bulk revocation 800 // for this data type occurred. It's pointless to update the 801 // heuristics at this point so simply update the header with a 802 // CAS. If we fail this race, the object's bias has been revoked 803 // by another thread so we simply return and let the caller deal 804 // with it. 805 obj->cas_set_mark(prototype_header.set_age(mark.age()), mark); 806 assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked"); 807 return BIAS_REVOKED; 808 } else if (prototype_header.bias_epoch() != mark.bias_epoch()) { 809 // The epoch of this biasing has expired indicating that the 810 // object is effectively unbiased. Depending on whether we need 811 // to rebias or revoke the bias of this object we can do it 812 // efficiently enough with a CAS that we shouldn't update the 813 // heuristics. This is normally done in the assembly code but we 814 // can reach this point due to various points in the runtime 815 // needing to revoke biases. 816 markWord res_mark; 817 if (attempt_rebias) { 818 assert(THREAD->is_Java_thread(), ""); 819 markWord biased_value = mark; 820 markWord rebiased_prototype = markWord::encode((JavaThread*) THREAD, mark.age(), prototype_header.bias_epoch()); 821 res_mark = obj->cas_set_mark(rebiased_prototype, mark); 822 if (res_mark == biased_value) { 823 return BIAS_REVOKED_AND_REBIASED; 824 } 825 } else { 826 markWord biased_value = mark; 827 markWord unbiased_prototype = markWord::prototype().set_age(mark.age()); 828 res_mark = obj->cas_set_mark(unbiased_prototype, mark); 829 if (res_mark == biased_value) { 830 return BIAS_REVOKED; 831 } 832 } 833 mark = res_mark; // Refresh mark with the latest value. 834 } 835 } 836 837 HeuristicsResult heuristics = update_heuristics(obj()); 838 if (heuristics == HR_NOT_BIASED) { 839 return NOT_BIASED; 840 } else if (heuristics == HR_SINGLE_REVOKE) { 841 JavaThread *blt = mark.biased_locker(); 842 assert(blt != NULL, "invariant"); 843 if (blt == THREAD) { 844 // A thread is trying to revoke the bias of an object biased 845 // toward it, again likely due to an identity hash code 846 // computation. We can again avoid a safepoint/handshake in this case 847 // since we are only going to walk our own stack. There are no 848 // races with revocations occurring in other threads because we 849 // reach no safepoints in the revocation path. 850 EventBiasedLockSelfRevocation event; 851 ResourceMark rm; 852 walk_stack_and_revoke(obj(), blt); 853 blt->set_cached_monitor_info(NULL); 854 assert(!obj->mark().has_bias_pattern(), "invariant"); 855 if (event.should_commit()) { 856 post_self_revocation_event(&event, obj->klass()); 857 } 858 return BIAS_REVOKED; 859 } else { 860 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt); 861 if (cond != NOT_REVOKED) { 862 return cond; 863 } 864 } 865 } else { 866 assert((heuristics == HR_BULK_REVOKE) || 867 (heuristics == HR_BULK_REBIAS), "?"); 868 EventBiasedLockClassRevocation event; 869 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD, 870 (heuristics == HR_BULK_REBIAS), 871 attempt_rebias); 872 VMThread::execute(&bulk_revoke); 873 if (event.should_commit()) { 874 post_class_revocation_event(&event, obj->klass(), &bulk_revoke); 875 } 876 return bulk_revoke.status_code(); 877 } 878 } 879 } 880 881 // All objects in objs should be locked by biaser 882 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) { 883 bool clean_my_cache = false; 884 for (int i = 0; i < objs->length(); i++) { 885 oop obj = (objs->at(i))(); 886 markWord mark = obj->mark(); 887 if (mark.has_bias_pattern()) { 888 walk_stack_and_revoke(obj, biaser); 889 clean_my_cache = true; 890 } 891 } 892 if (clean_my_cache) { 893 clean_up_cached_monitor_info(biaser); 894 } 895 } 896 897 898 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 899 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 900 oop obj = h_obj(); 901 HeuristicsResult heuristics = update_heuristics(obj); 902 if (heuristics == HR_SINGLE_REVOKE) { 903 JavaThread* biased_locker = NULL; 904 single_revoke_at_safepoint(obj, false, false, NULL, &biased_locker); 905 if (biased_locker) { 906 clean_up_cached_monitor_info(biased_locker); 907 } 908 } else if ((heuristics == HR_BULK_REBIAS) || 909 (heuristics == HR_BULK_REVOKE)) { 910 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 911 clean_up_cached_monitor_info(); 912 } 913 } 914 915 916 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 917 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 918 int len = objs->length(); 919 for (int i = 0; i < len; i++) { 920 oop obj = (objs->at(i))(); 921 HeuristicsResult heuristics = update_heuristics(obj); 922 if (heuristics == HR_SINGLE_REVOKE) { 923 single_revoke_at_safepoint(obj, false, false, NULL, NULL); 924 } else if ((heuristics == HR_BULK_REBIAS) || 925 (heuristics == HR_BULK_REVOKE)) { 926 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 927 } 928 } 929 clean_up_cached_monitor_info(); 930 } 931 932 933 void BiasedLocking::preserve_marks() { 934 if (!UseBiasedLocking) 935 return; 936 937 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 938 939 assert(_preserved_oop_stack == NULL, "double initialization"); 940 assert(_preserved_mark_stack == NULL, "double initialization"); 941 942 // In order to reduce the number of mark words preserved during GC 943 // due to the presence of biased locking, we reinitialize most mark 944 // words to the class's prototype during GC -- even those which have 945 // a currently valid bias owner. One important situation where we 946 // must not clobber a bias is when a biased object is currently 947 // locked. To handle this case we iterate over the currently-locked 948 // monitors in a prepass and, if they are biased, preserve their 949 // mark words here. This should be a relatively small set of objects 950 // especially compared to the number of objects in the heap. 951 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true); 952 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 953 954 ResourceMark rm; 955 Thread* cur = Thread::current(); 956 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) { 957 if (thread->has_last_Java_frame()) { 958 RegisterMap rm(thread); 959 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 960 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 961 if (monitors != NULL) { 962 int len = monitors->length(); 963 // Walk monitors youngest to oldest 964 for (int i = len - 1; i >= 0; i--) { 965 MonitorInfo* mon_info = monitors->at(i); 966 if (mon_info->owner_is_scalar_replaced()) continue; 967 oop owner = mon_info->owner(); 968 if (owner != NULL) { 969 markWord mark = owner->mark(); 970 if (mark.has_bias_pattern()) { 971 _preserved_oop_stack->push(Handle(cur, owner)); 972 _preserved_mark_stack->push(mark); 973 } 974 } 975 } 976 } 977 } 978 } 979 } 980 } 981 982 983 void BiasedLocking::restore_marks() { 984 if (!UseBiasedLocking) 985 return; 986 987 assert(_preserved_oop_stack != NULL, "double free"); 988 assert(_preserved_mark_stack != NULL, "double free"); 989 990 int len = _preserved_oop_stack->length(); 991 for (int i = 0; i < len; i++) { 992 Handle owner = _preserved_oop_stack->at(i); 993 markWord mark = _preserved_mark_stack->at(i); 994 owner->set_mark(mark); 995 } 996 997 delete _preserved_oop_stack; 998 _preserved_oop_stack = NULL; 999 delete _preserved_mark_stack; 1000 _preserved_mark_stack = NULL; 1001 } 1002 1003 1004 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 1005 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 1006 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 1007 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 1008 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 1009 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); } 1010 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 1011 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 1012 1013 1014 // BiasedLockingCounters 1015 1016 int BiasedLockingCounters::slow_path_entry_count() const { 1017 if (_slow_path_entry_count != 0) { 1018 return _slow_path_entry_count; 1019 } 1020 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 1021 _rebiased_lock_entry_count + _revoked_lock_entry_count + 1022 _fast_path_entry_count; 1023 1024 return _total_entry_count - sum; 1025 } 1026 1027 void BiasedLockingCounters::print_on(outputStream* st) const { 1028 tty->print_cr("# total entries: %d", _total_entry_count); 1029 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 1030 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 1031 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 1032 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 1033 tty->print_cr("# handshakes entries: %d", _handshakes_count); 1034 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 1035 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 1036 } 1037 1038 void BiasedLockingCounters::print() const { print_on(tty); }