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