1 /* 2 * Copyright (c) 2005, 2016, 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 "logging/log.hpp" 27 #include "memory/resourceArea.hpp" 28 #include "oops/klass.inline.hpp" 29 #include "oops/markOop.hpp" 30 #include "oops/oop.inline.hpp" 31 #include "runtime/atomic.hpp" 32 #include "runtime/basicLock.hpp" 33 #include "runtime/biasedLocking.hpp" 34 #include "runtime/task.hpp" 35 #include "runtime/vframe.hpp" 36 #include "runtime/vmThread.hpp" 37 #include "runtime/vm_operations.hpp" 38 39 static bool _biased_locking_enabled = false; 40 BiasedLockingCounters BiasedLocking::_counters; 41 42 static GrowableArray<Handle>* _preserved_oop_stack = NULL; 43 static GrowableArray<markOop>* _preserved_mark_stack = NULL; 44 45 static void enable_biased_locking(Klass* k) { 46 k->set_prototype_header(markOopDesc::biased_locking_prototype()); 47 } 48 49 class VM_EnableBiasedLocking: public VM_Operation { 50 private: 51 bool _is_cheap_allocated; 52 public: 53 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } 54 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } 55 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } 56 bool is_cheap_allocated() const { return _is_cheap_allocated; } 57 58 void doit() { 59 // Iterate the system dictionary enabling biased locking for all 60 // currently loaded classes 61 SystemDictionary::classes_do(enable_biased_locking); 62 // Indicate that future instances should enable it as well 63 _biased_locking_enabled = true; 64 65 log_info(biasedlocking)("Biased locking enabled"); 66 } 67 68 bool allow_nested_vm_operations() const { return false; } 69 }; 70 71 72 // One-shot PeriodicTask subclass for enabling biased locking 73 class EnableBiasedLockingTask : public PeriodicTask { 74 public: 75 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} 76 77 virtual void task() { 78 // Use async VM operation to avoid blocking the Watcher thread. 79 // VM Thread will free C heap storage. 80 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); 81 VMThread::execute(op); 82 83 // Reclaim our storage and disenroll ourself 84 delete this; 85 } 86 }; 87 88 89 void BiasedLocking::init() { 90 // If biased locking is enabled, schedule a task to fire a few 91 // seconds into the run which turns on biased locking for all 92 // currently loaded classes as well as future ones. This is a 93 // workaround for startup time regressions due to a large number of 94 // safepoints being taken during VM startup for bias revocation. 95 // Ideally we would have a lower cost for individual bias revocation 96 // and not need a mechanism like this. 97 if (UseBiasedLocking) { 98 if (BiasedLockingStartupDelay > 0) { 99 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); 100 task->enroll(); 101 } else { 102 VM_EnableBiasedLocking op(false); 103 VMThread::execute(&op); 104 } 105 } 106 } 107 108 109 bool BiasedLocking::enabled() { 110 return _biased_locking_enabled; 111 } 112 113 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order 114 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { 115 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); 116 if (info != NULL) { 117 return info; 118 } 119 120 info = new GrowableArray<MonitorInfo*>(); 121 122 // It's possible for the thread to not have any Java frames on it, 123 // i.e., if it's the main thread and it's already returned from main() 124 if (thread->has_last_Java_frame()) { 125 RegisterMap rm(thread); 126 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 127 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 128 if (monitors != NULL) { 129 int len = monitors->length(); 130 // Walk monitors youngest to oldest 131 for (int i = len - 1; i >= 0; i--) { 132 MonitorInfo* mon_info = monitors->at(i); 133 if (mon_info->eliminated()) continue; 134 oop owner = mon_info->owner(); 135 if (owner != NULL) { 136 info->append(mon_info); 137 } 138 } 139 } 140 } 141 } 142 143 thread->set_cached_monitor_info(info); 144 return info; 145 } 146 147 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { 148 markOop mark = obj->mark(); 149 if (!mark->has_bias_pattern()) { 150 if (log_is_enabled(Info, biasedlocking)) { 151 ResourceMark rm; 152 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT 153 ", mark " INTPTR_FORMAT ", type %s" 154 ", requesting thread " INTPTR_FORMAT 155 " because it's no longer biased)", 156 p2i((void *)obj), (intptr_t) mark, 157 obj->klass()->external_name(), 158 (intptr_t) requesting_thread); 159 } 160 return BiasedLocking::NOT_BIASED; 161 } 162 163 uint age = mark->age(); 164 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); 165 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); 166 167 // Log at "info" level if not bulk, else "trace" level 168 if (!is_bulk) { 169 ResourceMark rm; 170 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark " 171 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT 172 ", allow rebias %d, requesting thread " INTPTR_FORMAT, 173 p2i((void *)obj), 174 (intptr_t) mark, 175 obj->klass()->external_name(), 176 (intptr_t) obj->klass()->prototype_header(), 177 (allow_rebias ? 1 : 0), 178 (intptr_t) requesting_thread); 179 } else { 180 ResourceMark rm; 181 log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark " 182 INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT 183 " , allow rebias %d , requesting thread " INTPTR_FORMAT, 184 p2i((void *)obj), 185 (intptr_t) mark, 186 obj->klass()->external_name(), 187 (intptr_t) obj->klass()->prototype_header(), 188 (allow_rebias ? 1 : 0), 189 (intptr_t) requesting_thread); 190 } 191 192 JavaThread* biased_thread = mark->biased_locker(); 193 if (biased_thread == NULL) { 194 // Object is anonymously biased. We can get here if, for 195 // example, we revoke the bias due to an identity hash code 196 // being computed for an object. 197 if (!allow_rebias) { 198 obj->set_mark(unbiased_prototype); 199 } 200 // Log at "info" level if not bulk, else "trace" level 201 if (!is_bulk) { 202 log_info(biasedlocking)(" Revoked bias of anonymously-biased object"); 203 } else { 204 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object"); 205 } 206 return BiasedLocking::BIAS_REVOKED; 207 } 208 209 // Handle case where the thread toward which the object was biased has exited 210 bool thread_is_alive = false; 211 if (requesting_thread == biased_thread) { 212 thread_is_alive = true; 213 } else { 214 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { 215 if (cur_thread == biased_thread) { 216 thread_is_alive = true; 217 break; 218 } 219 } 220 } 221 if (!thread_is_alive) { 222 if (allow_rebias) { 223 obj->set_mark(biased_prototype); 224 } else { 225 obj->set_mark(unbiased_prototype); 226 } 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 BiasedLocking::BIAS_REVOKED; 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 later 261 markOop mark = markOopDesc::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 storing the lock address for platforms without TSO 276 // ordering (e.g. ppc). 277 obj->release_set_mark(markOopDesc::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 if (allow_rebias) { 293 obj->set_mark(biased_prototype); 294 } else { 295 // Store the unlocked value into the object's header. 296 obj->set_mark(unbiased_prototype); 297 } 298 } 299 300 return BiasedLocking::BIAS_REVOKED; 301 } 302 303 304 enum HeuristicsResult { 305 HR_NOT_BIASED = 1, 306 HR_SINGLE_REVOKE = 2, 307 HR_BULK_REBIAS = 3, 308 HR_BULK_REVOKE = 4 309 }; 310 311 312 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { 313 markOop mark = o->mark(); 314 if (!mark->has_bias_pattern()) { 315 return HR_NOT_BIASED; 316 } 317 318 // Heuristics to attempt to throttle the number of revocations. 319 // Stages: 320 // 1. Revoke the biases of all objects in the heap of this type, 321 // but allow rebiasing of those objects if unlocked. 322 // 2. Revoke the biases of all objects in the heap of this type 323 // and don't allow rebiasing of these objects. Disable 324 // allocation of objects of that type with the bias bit set. 325 Klass* k = o->klass(); 326 jlong cur_time = os::javaTimeMillis(); 327 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); 328 int revocation_count = k->biased_lock_revocation_count(); 329 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && 330 (revocation_count < BiasedLockingBulkRevokeThreshold) && 331 (last_bulk_revocation_time != 0) && 332 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { 333 // This is the first revocation we've seen in a while of an 334 // object of this type since the last time we performed a bulk 335 // rebiasing operation. The application is allocating objects in 336 // bulk which are biased toward a thread and then handing them 337 // off to another thread. We can cope with this allocation 338 // pattern via the bulk rebiasing mechanism so we reset the 339 // klass's revocation count rather than allow it to increase 340 // monotonically. If we see the need to perform another bulk 341 // rebias operation later, we will, and if subsequently we see 342 // many more revocation operations in a short period of time we 343 // will completely disable biasing for this type. 344 k->set_biased_lock_revocation_count(0); 345 revocation_count = 0; 346 } 347 348 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold 349 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { 350 revocation_count = k->atomic_incr_biased_lock_revocation_count(); 351 } 352 353 if (revocation_count == BiasedLockingBulkRevokeThreshold) { 354 return HR_BULK_REVOKE; 355 } 356 357 if (revocation_count == BiasedLockingBulkRebiasThreshold) { 358 return HR_BULK_REBIAS; 359 } 360 361 return HR_SINGLE_REVOKE; 362 } 363 364 365 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, 366 bool bulk_rebias, 367 bool attempt_rebias_of_object, 368 JavaThread* requesting_thread) { 369 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); 370 371 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object " 372 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", 373 (bulk_rebias ? "rebias" : "revoke"), 374 p2i((void *) o), 375 (intptr_t) o->mark(), 376 o->klass()->external_name()); 377 378 jlong cur_time = os::javaTimeMillis(); 379 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time); 380 381 382 Klass* k_o = o->klass(); 383 Klass* klass = k_o; 384 385 if (bulk_rebias) { 386 // Use the epoch in the klass of the object to implicitly revoke 387 // all biases of objects of this data type and force them to be 388 // reacquired. However, we also need to walk the stacks of all 389 // threads and update the headers of lightweight locked objects 390 // with biases to have the current epoch. 391 392 // If the prototype header doesn't have the bias pattern, don't 393 // try to update the epoch -- assume another VM operation came in 394 // and reset the header to the unbiased state, which will 395 // implicitly cause all existing biases to be revoked 396 if (klass->prototype_header()->has_bias_pattern()) { 397 int prev_epoch = klass->prototype_header()->bias_epoch(); 398 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); 399 int cur_epoch = klass->prototype_header()->bias_epoch(); 400 401 // Now walk all threads' stacks and adjust epochs of any biased 402 // and locked objects of this data type we encounter 403 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 404 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 405 for (int i = 0; i < cached_monitor_info->length(); i++) { 406 MonitorInfo* mon_info = cached_monitor_info->at(i); 407 oop owner = mon_info->owner(); 408 markOop mark = owner->mark(); 409 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 410 // We might have encountered this object already in the case of recursive locking 411 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); 412 owner->set_mark(mark->set_bias_epoch(cur_epoch)); 413 } 414 } 415 } 416 } 417 418 // At this point we're done. All we have to do is potentially 419 // adjust the header of the given object to revoke its bias. 420 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); 421 } else { 422 if (log_is_enabled(Info, biasedlocking)) { 423 ResourceMark rm; 424 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name()); 425 } 426 427 // Disable biased locking for this data type. Not only will this 428 // cause future instances to not be biased, but existing biased 429 // instances will notice that this implicitly caused their biases 430 // to be revoked. 431 klass->set_prototype_header(markOopDesc::prototype()); 432 433 // Now walk all threads' stacks and forcibly revoke the biases of 434 // any locked and biased objects of this data type we encounter. 435 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 436 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); 437 for (int i = 0; i < cached_monitor_info->length(); i++) { 438 MonitorInfo* mon_info = cached_monitor_info->at(i); 439 oop owner = mon_info->owner(); 440 markOop mark = owner->mark(); 441 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { 442 revoke_bias(owner, false, true, requesting_thread); 443 } 444 } 445 } 446 447 // Must force the bias of the passed object to be forcibly revoked 448 // as well to ensure guarantees to callers 449 revoke_bias(o, false, true, requesting_thread); 450 } 451 452 log_info(biasedlocking)("* Ending bulk revocation"); 453 454 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; 455 456 if (attempt_rebias_of_object && 457 o->mark()->has_bias_pattern() && 458 klass->prototype_header()->has_bias_pattern()) { 459 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), 460 klass->prototype_header()->bias_epoch()); 461 o->set_mark(new_mark); 462 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; 463 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); 464 } 465 466 assert(!o->mark()->has_bias_pattern() || 467 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), 468 "bug in bulk bias revocation"); 469 470 return status_code; 471 } 472 473 474 static void clean_up_cached_monitor_info() { 475 // Walk the thread list clearing out the cached monitors 476 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { 477 thr->set_cached_monitor_info(NULL); 478 } 479 } 480 481 482 class VM_RevokeBias : public VM_Operation { 483 protected: 484 Handle* _obj; 485 GrowableArray<Handle>* _objs; 486 JavaThread* _requesting_thread; 487 BiasedLocking::Condition _status_code; 488 489 public: 490 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) 491 : _obj(obj) 492 , _objs(NULL) 493 , _requesting_thread(requesting_thread) 494 , _status_code(BiasedLocking::NOT_BIASED) {} 495 496 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) 497 : _obj(NULL) 498 , _objs(objs) 499 , _requesting_thread(requesting_thread) 500 , _status_code(BiasedLocking::NOT_BIASED) {} 501 502 virtual VMOp_Type type() const { return VMOp_RevokeBias; } 503 504 virtual bool doit_prologue() { 505 // Verify that there is actual work to do since the callers just 506 // give us locked object(s). If we don't find any biased objects 507 // there is nothing to do and we avoid a safepoint. 508 if (_obj != NULL) { 509 markOop mark = (*_obj)()->mark(); 510 if (mark->has_bias_pattern()) { 511 return true; 512 } 513 } else { 514 for ( int i = 0 ; i < _objs->length(); i++ ) { 515 markOop mark = (_objs->at(i))()->mark(); 516 if (mark->has_bias_pattern()) { 517 return true; 518 } 519 } 520 } 521 return false; 522 } 523 524 virtual void doit() { 525 if (_obj != NULL) { 526 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:"); 527 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); 528 clean_up_cached_monitor_info(); 529 return; 530 } else { 531 log_info(biasedlocking)("Revoking bias with global safepoint:"); 532 BiasedLocking::revoke_at_safepoint(_objs); 533 } 534 } 535 536 BiasedLocking::Condition status_code() const { 537 return _status_code; 538 } 539 }; 540 541 542 class VM_BulkRevokeBias : public VM_RevokeBias { 543 private: 544 bool _bulk_rebias; 545 bool _attempt_rebias_of_object; 546 547 public: 548 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, 549 bool bulk_rebias, 550 bool attempt_rebias_of_object) 551 : VM_RevokeBias(obj, requesting_thread) 552 , _bulk_rebias(bulk_rebias) 553 , _attempt_rebias_of_object(attempt_rebias_of_object) {} 554 555 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } 556 virtual bool doit_prologue() { return true; } 557 558 virtual void doit() { 559 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); 560 clean_up_cached_monitor_info(); 561 } 562 }; 563 564 565 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { 566 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 567 568 // We can revoke the biases of anonymously-biased objects 569 // efficiently enough that we should not cause these revocations to 570 // update the heuristics because doing so may cause unwanted bulk 571 // revocations (which are expensive) to occur. 572 markOop mark = obj->mark(); 573 if (mark->is_biased_anonymously() && !attempt_rebias) { 574 // We are probably trying to revoke the bias of this object due to 575 // an identity hash code computation. Try to revoke the bias 576 // without a safepoint. This is possible if we can successfully 577 // compare-and-exchange an unbiased header into the mark word of 578 // the object, meaning that no other thread has raced to acquire 579 // the bias of the object. 580 markOop biased_value = mark; 581 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 582 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark); 583 if (res_mark == biased_value) { 584 return BIAS_REVOKED; 585 } 586 } else if (mark->has_bias_pattern()) { 587 Klass* k = obj->klass(); 588 markOop prototype_header = k->prototype_header(); 589 if (!prototype_header->has_bias_pattern()) { 590 // This object has a stale bias from before the bulk revocation 591 // for this data type occurred. It's pointless to update the 592 // heuristics at this point so simply update the header with a 593 // CAS. If we fail this race, the object's bias has been revoked 594 // by another thread so we simply return and let the caller deal 595 // with it. 596 markOop biased_value = mark; 597 markOop res_mark = obj->cas_set_mark(prototype_header, mark); 598 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); 599 return BIAS_REVOKED; 600 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { 601 // The epoch of this biasing has expired indicating that the 602 // object is effectively unbiased. Depending on whether we need 603 // to rebias or revoke the bias of this object we can do it 604 // efficiently enough with a CAS that we shouldn't update the 605 // heuristics. This is normally done in the assembly code but we 606 // can reach this point due to various points in the runtime 607 // needing to revoke biases. 608 if (attempt_rebias) { 609 assert(THREAD->is_Java_thread(), ""); 610 markOop biased_value = mark; 611 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); 612 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark); 613 if (res_mark == biased_value) { 614 return BIAS_REVOKED_AND_REBIASED; 615 } 616 } else { 617 markOop biased_value = mark; 618 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); 619 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark); 620 if (res_mark == biased_value) { 621 return BIAS_REVOKED; 622 } 623 } 624 } 625 } 626 627 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); 628 if (heuristics == HR_NOT_BIASED) { 629 return NOT_BIASED; 630 } else if (heuristics == HR_SINGLE_REVOKE) { 631 Klass *k = obj->klass(); 632 markOop prototype_header = k->prototype_header(); 633 if (mark->biased_locker() == THREAD && 634 prototype_header->bias_epoch() == mark->bias_epoch()) { 635 // A thread is trying to revoke the bias of an object biased 636 // toward it, again likely due to an identity hash code 637 // computation. We can again avoid a safepoint in this case 638 // since we are only going to walk our own stack. There are no 639 // races with revocations occurring in other threads because we 640 // reach no safepoints in the revocation path. 641 // Also check the epoch because even if threads match, another thread 642 // can come in with a CAS to steal the bias of an object that has a 643 // stale epoch. 644 ResourceMark rm; 645 log_info(biasedlocking)("Revoking bias by walking my own stack:"); 646 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); 647 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); 648 assert(cond == BIAS_REVOKED, "why not?"); 649 return cond; 650 } else { 651 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); 652 VMThread::execute(&revoke); 653 return revoke.status_code(); 654 } 655 } 656 657 assert((heuristics == HR_BULK_REVOKE) || 658 (heuristics == HR_BULK_REBIAS), "?"); 659 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, 660 (heuristics == HR_BULK_REBIAS), 661 attempt_rebias); 662 VMThread::execute(&bulk_revoke); 663 return bulk_revoke.status_code(); 664 } 665 666 667 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { 668 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); 669 if (objs->length() == 0) { 670 return; 671 } 672 VM_RevokeBias revoke(objs, JavaThread::current()); 673 VMThread::execute(&revoke); 674 } 675 676 677 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { 678 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 679 oop obj = h_obj(); 680 HeuristicsResult heuristics = update_heuristics(obj, false); 681 if (heuristics == HR_SINGLE_REVOKE) { 682 revoke_bias(obj, false, false, NULL); 683 } else if ((heuristics == HR_BULK_REBIAS) || 684 (heuristics == HR_BULK_REVOKE)) { 685 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 686 } 687 clean_up_cached_monitor_info(); 688 } 689 690 691 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { 692 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 693 int len = objs->length(); 694 for (int i = 0; i < len; i++) { 695 oop obj = (objs->at(i))(); 696 HeuristicsResult heuristics = update_heuristics(obj, false); 697 if (heuristics == HR_SINGLE_REVOKE) { 698 revoke_bias(obj, false, false, NULL); 699 } else if ((heuristics == HR_BULK_REBIAS) || 700 (heuristics == HR_BULK_REVOKE)) { 701 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); 702 } 703 } 704 clean_up_cached_monitor_info(); 705 } 706 707 708 void BiasedLocking::preserve_marks() { 709 if (!UseBiasedLocking) 710 return; 711 712 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); 713 714 assert(_preserved_oop_stack == NULL, "double initialization"); 715 assert(_preserved_mark_stack == NULL, "double initialization"); 716 717 // In order to reduce the number of mark words preserved during GC 718 // due to the presence of biased locking, we reinitialize most mark 719 // words to the class's prototype during GC -- even those which have 720 // a currently valid bias owner. One important situation where we 721 // must not clobber a bias is when a biased object is currently 722 // locked. To handle this case we iterate over the currently-locked 723 // monitors in a prepass and, if they are biased, preserve their 724 // mark words here. This should be a relatively small set of objects 725 // especially compared to the number of objects in the heap. 726 _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true); 727 _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true); 728 729 ResourceMark rm; 730 Thread* cur = Thread::current(); 731 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { 732 if (thread->has_last_Java_frame()) { 733 RegisterMap rm(thread); 734 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { 735 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); 736 if (monitors != NULL) { 737 int len = monitors->length(); 738 // Walk monitors youngest to oldest 739 for (int i = len - 1; i >= 0; i--) { 740 MonitorInfo* mon_info = monitors->at(i); 741 if (mon_info->owner_is_scalar_replaced()) continue; 742 oop owner = mon_info->owner(); 743 if (owner != NULL) { 744 markOop mark = owner->mark(); 745 if (mark->has_bias_pattern()) { 746 _preserved_oop_stack->push(Handle(cur, owner)); 747 _preserved_mark_stack->push(mark); 748 } 749 } 750 } 751 } 752 } 753 } 754 } 755 } 756 757 758 void BiasedLocking::restore_marks() { 759 if (!UseBiasedLocking) 760 return; 761 762 assert(_preserved_oop_stack != NULL, "double free"); 763 assert(_preserved_mark_stack != NULL, "double free"); 764 765 int len = _preserved_oop_stack->length(); 766 for (int i = 0; i < len; i++) { 767 Handle owner = _preserved_oop_stack->at(i); 768 markOop mark = _preserved_mark_stack->at(i); 769 owner->set_mark(mark); 770 } 771 772 delete _preserved_oop_stack; 773 _preserved_oop_stack = NULL; 774 delete _preserved_mark_stack; 775 _preserved_mark_stack = NULL; 776 } 777 778 779 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } 780 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } 781 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } 782 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } 783 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } 784 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } 785 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } 786 787 788 // BiasedLockingCounters 789 790 int BiasedLockingCounters::slow_path_entry_count() { 791 if (_slow_path_entry_count != 0) { 792 return _slow_path_entry_count; 793 } 794 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + 795 _rebiased_lock_entry_count + _revoked_lock_entry_count + 796 _fast_path_entry_count; 797 798 return _total_entry_count - sum; 799 } 800 801 void BiasedLockingCounters::print_on(outputStream* st) { 802 tty->print_cr("# total entries: %d", _total_entry_count); 803 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); 804 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); 805 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); 806 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); 807 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); 808 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); 809 }