rev 57079 : imported patch 8234796

   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 void BiasedLocking::single_revoke_at_safepoint(oop obj, 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;
 177   }
 178 
 179   uint age = mark.age();
 180   markWord unbiased_prototype = markWord::prototype().set_age(age);
 181 
 182   // Log at "info" level if not bulk, else "trace" level
 183   if (!is_bulk) {
 184     ResourceMark rm;
 185     log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
 186                             INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
 187                             ", requesting thread " INTPTR_FORMAT,
 188                             p2i((void *)obj),
 189                             mark.value(),
 190                             obj->klass()->external_name(),
 191                             obj->klass()->prototype_header().value(),
 192                             (intptr_t) requesting_thread);
 193   } else {
 194     ResourceMark rm;
 195     log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
 196                              INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
 197                              " , requesting thread " INTPTR_FORMAT,
 198                              p2i((void *)obj),
 199                              mark.value(),
 200                              obj->klass()->external_name(),
 201                              obj->klass()->prototype_header().value(),
 202                              (intptr_t) requesting_thread);
 203   }
 204 
 205   JavaThread* biased_thread = mark.biased_locker();
 206   if (biased_thread == NULL) {
 207     // Object is anonymously biased. We can get here if, for
 208     // example, we revoke the bias due to an identity hash code
 209     // being computed for an object.
 210     obj->set_mark(unbiased_prototype);
 211 
 212     // Log at "info" level if not bulk, else "trace" level
 213     if (!is_bulk) {
 214       log_info(biasedlocking)("  Revoked bias of anonymously-biased object");
 215     } else {
 216       log_trace(biasedlocking)("  Revoked bias of anonymously-biased object");
 217     }
 218     return;
 219   }
 220 
 221   // Handle case where the thread toward which the object was biased has exited
 222   bool thread_is_alive = false;
 223   if (requesting_thread == biased_thread) {
 224     thread_is_alive = true;
 225   } else {
 226     ThreadsListHandle tlh;
 227     thread_is_alive = tlh.includes(biased_thread);
 228   }
 229   if (!thread_is_alive) {
 230     obj->set_mark(unbiased_prototype);
 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;
 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 (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 below
 265       markWord mark = markWord::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 store the lock address for platforms without TSO
 280     // ordering (e.g. ppc).
 281     obj->release_set_mark(markWord::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     // Store the unlocked value into the object's header.
 297     obj->set_mark(unbiased_prototype);
 298   }
 299 
 300   // If requested, return information on which thread held the bias
 301   if (biased_locker != NULL) {
 302     *biased_locker = biased_thread;
 303   }
 304 }
 305 
 306 
 307 enum HeuristicsResult {
 308   HR_NOT_BIASED    = 1,
 309   HR_SINGLE_REVOKE = 2,
 310   HR_BULK_REBIAS   = 3,
 311   HR_BULK_REVOKE   = 4
 312 };
 313 
 314 
 315 static HeuristicsResult update_heuristics(oop o) {
 316   markWord mark = o->mark();
 317   if (!mark.has_bias_pattern()) {
 318     return HR_NOT_BIASED;
 319   }
 320 
 321   // Heuristics to attempt to throttle the number of revocations.
 322   // Stages:
 323   // 1. Revoke the biases of all objects in the heap of this type,
 324   //    but allow rebiasing of those objects if unlocked.
 325   // 2. Revoke the biases of all objects in the heap of this type
 326   //    and don't allow rebiasing of these objects. Disable
 327   //    allocation of objects of that type with the bias bit set.
 328   Klass* k = o->klass();
 329   jlong cur_time = os::javaTimeMillis();
 330   jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
 331   int revocation_count = k->biased_lock_revocation_count();
 332   if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
 333       (revocation_count <  BiasedLockingBulkRevokeThreshold) &&
 334       (last_bulk_revocation_time != 0) &&
 335       (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
 336     // This is the first revocation we've seen in a while of an
 337     // object of this type since the last time we performed a bulk
 338     // rebiasing operation. The application is allocating objects in
 339     // bulk which are biased toward a thread and then handing them
 340     // off to another thread. We can cope with this allocation
 341     // pattern via the bulk rebiasing mechanism so we reset the
 342     // klass's revocation count rather than allow it to increase
 343     // monotonically. If we see the need to perform another bulk
 344     // rebias operation later, we will, and if subsequently we see
 345     // many more revocation operations in a short period of time we
 346     // will completely disable biasing for this type.
 347     k->set_biased_lock_revocation_count(0);
 348     revocation_count = 0;
 349   }
 350 
 351   // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
 352   if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
 353     revocation_count = k->atomic_incr_biased_lock_revocation_count();
 354   }
 355 
 356   if (revocation_count == BiasedLockingBulkRevokeThreshold) {
 357     return HR_BULK_REVOKE;
 358   }
 359 
 360   if (revocation_count == BiasedLockingBulkRebiasThreshold) {
 361     return HR_BULK_REBIAS;
 362   }
 363 
 364   return HR_SINGLE_REVOKE;
 365 }
 366 
 367 
 368 void BiasedLocking::bulk_revoke_at_safepoint(oop o, bool bulk_rebias, JavaThread* requesting_thread) {
 369   assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
 370   assert(Thread::current()->is_VM_thread(), "must be VMThread");
 371 
 372   log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
 373                           INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
 374                           (bulk_rebias ? "rebias" : "revoke"),
 375                           p2i((void *) o),
 376                           o->mark().value(),
 377                           o->klass()->external_name());
 378 
 379   jlong cur_time = os::javaTimeMillis();
 380   o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
 381 
 382   Klass* k_o = o->klass();
 383   Klass* klass = k_o;
 384 
 385   {
 386     JavaThreadIteratorWithHandle jtiwh;
 387 
 388     if (bulk_rebias) {
 389       // Use the epoch in the klass of the object to implicitly revoke
 390       // all biases of objects of this data type and force them to be
 391       // reacquired. However, we also need to walk the stacks of all
 392       // threads and update the headers of lightweight locked objects
 393       // with biases to have the current epoch.
 394 
 395       // If the prototype header doesn't have the bias pattern, don't
 396       // try to update the epoch -- assume another VM operation came in
 397       // and reset the header to the unbiased state, which will
 398       // implicitly cause all existing biases to be revoked
 399       if (klass->prototype_header().has_bias_pattern()) {
 400         int prev_epoch = klass->prototype_header().bias_epoch();
 401         klass->set_prototype_header(klass->prototype_header().incr_bias_epoch());
 402         int cur_epoch = klass->prototype_header().bias_epoch();
 403 
 404         // Now walk all threads' stacks and adjust epochs of any biased
 405         // and locked objects of this data type we encounter
 406         for (; JavaThread *thr = jtiwh.next(); ) {
 407           GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
 408           for (int i = 0; i < cached_monitor_info->length(); i++) {
 409             MonitorInfo* mon_info = cached_monitor_info->at(i);
 410             oop owner = mon_info->owner();
 411             markWord mark = owner->mark();
 412             if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
 413               // We might have encountered this object already in the case of recursive locking
 414               assert(mark.bias_epoch() == prev_epoch || mark.bias_epoch() == cur_epoch, "error in bias epoch adjustment");
 415               owner->set_mark(mark.set_bias_epoch(cur_epoch));
 416             }
 417           }
 418         }
 419       }
 420 
 421       // At this point we're done. All we have to do is potentially
 422       // adjust the header of the given object to revoke its bias.
 423       single_revoke_at_safepoint(o, true, requesting_thread, NULL);
 424     } else {
 425       if (log_is_enabled(Info, biasedlocking)) {
 426         ResourceMark rm;
 427         log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
 428       }
 429 
 430       // Disable biased locking for this data type. Not only will this
 431       // cause future instances to not be biased, but existing biased
 432       // instances will notice that this implicitly caused their biases
 433       // to be revoked.
 434       klass->set_prototype_header(markWord::prototype());
 435 
 436       // Now walk all threads' stacks and forcibly revoke the biases of
 437       // any locked and biased objects of this data type we encounter.
 438       for (; JavaThread *thr = jtiwh.next(); ) {
 439         GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
 440         for (int i = 0; i < cached_monitor_info->length(); i++) {
 441           MonitorInfo* mon_info = cached_monitor_info->at(i);
 442           oop owner = mon_info->owner();
 443           markWord mark = owner->mark();
 444           if ((owner->klass() == k_o) && mark.has_bias_pattern()) {
 445             single_revoke_at_safepoint(owner, true, requesting_thread, NULL);
 446           }
 447         }
 448       }
 449 
 450       // Must force the bias of the passed object to be forcibly revoked
 451       // as well to ensure guarantees to callers
 452       single_revoke_at_safepoint(o, true, requesting_thread, NULL);
 453     }
 454   } // ThreadsListHandle is destroyed here.
 455 
 456   log_info(biasedlocking)("* Ending bulk revocation");
 457 
 458   assert(!o->mark().has_bias_pattern(), "bug in bulk bias revocation");
 459 }
 460 
 461 
 462 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
 463   if (thread != NULL) {
 464     thread->set_cached_monitor_info(NULL);
 465   } else {
 466     // Walk the thread list clearing out the cached monitors
 467     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
 468       thr->set_cached_monitor_info(NULL);
 469     }
 470   }
 471 }
 472 
 473 
 474 class VM_BulkRevokeBias : public VM_Operation {
 475 private:
 476   Handle* _obj;
 477   JavaThread* _requesting_thread;
 478   bool _bulk_rebias;
 479   uint64_t _safepoint_id;
 480 
 481 public:
 482   VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
 483                     bool bulk_rebias)
 484     : _obj(obj)
 485     , _requesting_thread(requesting_thread)
 486     , _bulk_rebias(bulk_rebias)
 487     , _safepoint_id(0) {}
 488 
 489   virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
 490 
 491   virtual void doit() {
 492     BiasedLocking::bulk_revoke_at_safepoint((*_obj)(), _bulk_rebias, _requesting_thread);
 493     _safepoint_id = SafepointSynchronize::safepoint_id();
 494     clean_up_cached_monitor_info();
 495   }
 496 
 497   bool is_bulk_rebias() const {
 498     return _bulk_rebias;
 499   }
 500 
 501   uint64_t safepoint_id() const {
 502     return _safepoint_id;
 503   }
 504 };
 505 
 506 
 507 class RevokeOneBias : public ThreadClosure {
 508 protected:
 509   Handle _obj;
 510   JavaThread* _requesting_thread;
 511   JavaThread* _biased_locker;
 512   BiasedLocking::Condition _status_code;
 513   traceid _biased_locker_id;
 514 
 515 public:
 516   RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
 517     : _obj(obj)

 518     , _requesting_thread(requesting_thread)
 519     , _biased_locker(biased_locker)
 520     , _status_code(BiasedLocking::NOT_BIASED)
 521     , _biased_locker_id(0) {}
 522 
 523   void do_thread(Thread* target) {
 524     assert(target == _biased_locker, "Wrong thread");
 525 
 526     oop o = _obj();
 527     markWord mark = o->mark();
 528 
 529     if (!mark.has_bias_pattern()) {
 530       return;
 531     }
 532 
 533     markWord prototype = o->klass()->prototype_header();
 534     if (!prototype.has_bias_pattern()) {
 535       // This object has a stale bias from before the handshake
 536       // was requested. If we fail this race, the object's bias
 537       // has been revoked by another thread so we simply return.
 538       markWord biased_value = mark;
 539       mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
 540       assert(!o->mark().has_bias_pattern(), "even if we raced, should still be revoked");
 541       if (biased_value == mark) {
 542         _status_code = BiasedLocking::BIAS_REVOKED;
 543       }
 544       return;
 545     }
 546 
 547     if (_biased_locker == mark.biased_locker()) {
 548       if (mark.bias_epoch() == prototype.bias_epoch()) {
 549         // Epoch is still valid. This means biaser could be currently
 550         // synchronized on this object. We must walk its stack looking
 551         // for monitor records associated with this object and change
 552         // them to be stack locks if any are found.
 553         ResourceMark rm;
 554         BiasedLocking::walk_stack_and_revoke(o, _biased_locker);
 555         _biased_locker->set_cached_monitor_info(NULL);
 556         assert(!o->mark().has_bias_pattern(), "invariant");
 557         _biased_locker_id = JFR_THREAD_ID(_biased_locker);
 558         _status_code = BiasedLocking::BIAS_REVOKED;
 559         return;
 560       } else {
 561         markWord biased_value = mark;
 562         mark = o->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
 563         if (mark == biased_value || !mark.has_bias_pattern()) {
 564           assert(!o->mark().has_bias_pattern(), "should be revoked");
 565           _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED;
 566           return;
 567         }
 568       }
 569     }
 570 
 571     _status_code = BiasedLocking::NOT_REVOKED;
 572   }
 573 
 574   BiasedLocking::Condition status_code() const {
 575     return _status_code;
 576   }
 577 
 578   traceid biased_locker() const {
 579     return _biased_locker_id;
 580   }
 581 };
 582 
 583 
 584 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
 585   assert(event != NULL, "invariant");
 586   assert(k != NULL, "invariant");
 587   assert(event->should_commit(), "invariant");
 588   event->set_lockClass(k);
 589   event->commit();
 590 }
 591 
 592 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) {
 593   assert(event != NULL, "invariant");
 594   assert(k != NULL, "invariant");
 595   assert(op != NULL, "invariant");
 596   assert(event->should_commit(), "invariant");
 597   event->set_lockClass(k);
 598   event->set_safepointId(0);
 599   event->set_previousOwner(op->biased_locker());
 600   event->commit();
 601 }
 602 
 603 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
 604   assert(event != NULL, "invariant");
 605   assert(k != NULL, "invariant");
 606   assert(op != NULL, "invariant");
 607   assert(event->should_commit(), "invariant");
 608   event->set_revokedClass(k);
 609   event->set_disableBiasing(!op->is_bulk_rebias());
 610   event->set_safepointId(op->safepoint_id());
 611   event->commit();
 612 }
 613 
 614 
 615 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) {
 616 
 617   EventBiasedLockRevocation event;
 618   if (PrintBiasedLockingStatistics) {
 619     Atomic::inc(handshakes_count_addr());
 620   }
 621   log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread "
 622                                      INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester),
 623                                      p2i(biaser), p2i(obj()));
 624 
 625   RevokeOneBias revoke(obj, requester, biaser);
 626   bool executed = Handshake::execute(&revoke, biaser);
 627   if (revoke.status_code() == NOT_REVOKED) {
 628     return NOT_REVOKED;
 629   }
 630   if (executed) {
 631     log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked",
 632                                        p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already "));
 633     if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) {
 634       post_revocation_event(&event, obj->klass(), &revoke);
 635     }
 636     assert(!obj->mark().has_bias_pattern(), "invariant");
 637     return revoke.status_code();
 638   } else {
 639     // Thread was not alive.
 640     // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly
 641     // created JavaThread (that happens to get the same memory address as biaser) synchronizing
 642     // on this object.
 643     {
 644       MutexLocker ml(Threads_lock);
 645       markWord mark = obj->mark();
 646       // Check if somebody else was able to revoke it before biased thread exited.
 647       if (!mark.has_bias_pattern()) {
 648         return NOT_BIASED;
 649       }
 650       ThreadsListHandle tlh;
 651       markWord prototype = obj->klass()->prototype_header();
 652       if (!prototype.has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark.biased_locker() &&
 653                                             prototype.bias_epoch() == mark.bias_epoch())) {
 654         obj->cas_set_mark(markWord::prototype().set_age(mark.age()), mark);
 655         if (event.should_commit()) {
 656           post_revocation_event(&event, obj->klass(), &revoke);
 657         }
 658         assert(!obj->mark().has_bias_pattern(), "bias should be revoked by now");
 659         return BIAS_REVOKED;
 660       }
 661     }
 662   }
 663 
 664   return NOT_REVOKED;
 665 }
 666 
 667 
 668 // Caller should have instantiated a ResourceMark object before calling this method
 669 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) {
 670   assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes,
 671          "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints");
 672   assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
 673 
 674   markWord mark = obj->mark();
 675   assert(mark.biased_locker() == biased_locker &&
 676          obj->klass()->prototype_header().bias_epoch() == mark.bias_epoch(), "invariant");
 677 
 678   log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
 679                            INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
 680                            ", biaser " INTPTR_FORMAT " %s",
 681                            Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread",
 682                            p2i(Thread::current()),
 683                            p2i(obj),
 684                            mark.value(),
 685                            obj->klass()->external_name(),
 686                            obj->klass()->prototype_header().value(),
 687                            p2i(biased_locker),
 688                            Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
 689 
 690   markWord unbiased_prototype = markWord::prototype().set_age(obj->mark().age());
 691 
 692   GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
 693   BasicLock* highest_lock = NULL;
 694   for (int i = 0; i < cached_monitor_info->length(); i++) {
 695     MonitorInfo* mon_info = cached_monitor_info->at(i);
 696     if (mon_info->owner() == obj) {
 697       log_trace(biasedlocking)("   mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
 698                                p2i(mon_info->owner()),
 699                                p2i(obj));
 700       // Assume recursive case and fix up highest lock below
 701       markWord mark = markWord::encode((BasicLock*) NULL);
 702       highest_lock = mon_info->lock();
 703       highest_lock->set_displaced_header(mark);
 704     } else {
 705       log_trace(biasedlocking)("   mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
 706                                p2i(mon_info->owner()),
 707                                p2i(obj));
 708     }
 709   }
 710   if (highest_lock != NULL) {
 711     // Fix up highest lock to contain displaced header and point
 712     // object at it
 713     highest_lock->set_displaced_header(unbiased_prototype);
 714     // Reset object header to point to displaced mark.
 715     // Must release store the lock address for platforms without TSO
 716     // ordering (e.g. ppc).
 717     obj->release_set_mark(markWord::encode(highest_lock));
 718     assert(!obj->mark().has_bias_pattern(), "illegal mark state: stack lock used bias bit");
 719     log_info(biasedlocking)("  Revoked bias of currently-locked object");
 720   } else {
 721     log_info(biasedlocking)("  Revoked bias of currently-unlocked object");
 722     // Store the unlocked value into the object's header.
 723     obj->set_mark(unbiased_prototype);
 724   }
 725 
 726   assert(!obj->mark().has_bias_pattern(), "must not be biased");
 727 }
 728 
 729 void BiasedLocking::revoke_own_lock(Handle obj, TRAPS) {
 730   assert(THREAD->is_Java_thread(), "must be called by a JavaThread");
 731   JavaThread* thread = (JavaThread*)THREAD;
 732 
 733   markWord mark = obj->mark();
 734 
 735   if (!mark.has_bias_pattern()) {
 736     return;
 737   }
 738 
 739   Klass *k = obj->klass();
 740   assert(mark.biased_locker() == thread &&
 741          k->prototype_header().bias_epoch() == mark.bias_epoch(), "Revoke failed, unhandled biased lock state");
 742   ResourceMark rm;
 743   log_info(biasedlocking)("Revoking bias by walking my own stack:");
 744   EventBiasedLockSelfRevocation event;
 745   BiasedLocking::walk_stack_and_revoke(obj(), (JavaThread*) thread);
 746   thread->set_cached_monitor_info(NULL);
 747   assert(!obj->mark().has_bias_pattern(), "invariant");
 748   if (event.should_commit()) {
 749     post_self_revocation_event(&event, k);
 750   }
 751 }
 752 
 753 void BiasedLocking::revoke(Handle obj, TRAPS) {
 754   assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
 755 
 756   while (true) {
 757     // We can revoke the biases of anonymously-biased objects
 758     // efficiently enough that we should not cause these revocations to
 759     // update the heuristics because doing so may cause unwanted bulk
 760     // revocations (which are expensive) to occur.
 761     markWord mark = obj->mark();
 762 
 763     if (!mark.has_bias_pattern()) {
 764       return;
 765     }
 766 
 767     if (mark.is_biased_anonymously()) {
 768       // We are probably trying to revoke the bias of this object due to
 769       // an identity hash code computation. Try to revoke the bias
 770       // without a safepoint. This is possible if we can successfully
 771       // compare-and-exchange an unbiased header into the mark word of
 772       // the object, meaning that no other thread has raced to acquire
 773       // the bias of the object.
 774       markWord biased_value       = mark;
 775       markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
 776       markWord res_mark = obj->cas_set_mark(unbiased_prototype, mark);
 777       if (res_mark == biased_value) {
 778         return;
 779       }
 780       mark = res_mark;  // Refresh mark with the latest value.
 781     } else {
 782       Klass* k = obj->klass();
 783       markWord prototype_header = k->prototype_header();
 784       if (!prototype_header.has_bias_pattern()) {
 785         // This object has a stale bias from before the bulk revocation
 786         // for this data type occurred. It's pointless to update the
 787         // heuristics at this point so simply update the header with a
 788         // CAS. If we fail this race, the object's bias has been revoked
 789         // by another thread so we simply return and let the caller deal
 790         // with it.
 791         obj->cas_set_mark(prototype_header.set_age(mark.age()), mark);
 792         assert(!obj->mark().has_bias_pattern(), "even if we raced, should still be revoked");
 793         return;
 794       } else if (prototype_header.bias_epoch() != mark.bias_epoch()) {
 795         // The epoch of this biasing has expired indicating that the
 796         // object is effectively unbiased. We can revoke the bias of this
 797         // object efficiently enough with a CAS that we shouldn't update the
 798         // heuristics. This is normally done in the assembly code but we
 799         // can reach this point due to various points in the runtime
 800         // needing to revoke biases.
 801         markWord res_mark;
 802         markWord biased_value       = mark;
 803         markWord unbiased_prototype = markWord::prototype().set_age(mark.age());
 804         res_mark = obj->cas_set_mark(unbiased_prototype, mark);
 805         if (res_mark == biased_value) {
 806           return;
 807         }
 808         mark = res_mark;  // Refresh mark with the latest value.
 809       }
 810     }
 811 
 812     HeuristicsResult heuristics = update_heuristics(obj());
 813     if (heuristics == HR_NOT_BIASED) {
 814       return;
 815     } else if (heuristics == HR_SINGLE_REVOKE) {
 816       JavaThread *blt = mark.biased_locker();
 817       assert(blt != NULL, "invariant");
 818       if (blt == THREAD) {
 819         // A thread is trying to revoke the bias of an object biased
 820         // toward it, again likely due to an identity hash code
 821         // computation. We can again avoid a safepoint/handshake in this case
 822         // since we are only going to walk our own stack. There are no
 823         // races with revocations occurring in other threads because we
 824         // reach no safepoints in the revocation path.
 825         EventBiasedLockSelfRevocation event;
 826         ResourceMark rm;
 827         walk_stack_and_revoke(obj(), blt);
 828         blt->set_cached_monitor_info(NULL);
 829         assert(!obj->mark().has_bias_pattern(), "invariant");
 830         if (event.should_commit()) {
 831           post_self_revocation_event(&event, obj->klass());
 832         }
 833         return;
 834       } else {
 835         BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
 836         if (cond != NOT_REVOKED) {
 837           return;
 838         }
 839       }
 840     } else {
 841       assert((heuristics == HR_BULK_REVOKE) ||
 842          (heuristics == HR_BULK_REBIAS), "?");
 843       EventBiasedLockClassRevocation event;
 844       VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
 845                                     (heuristics == HR_BULK_REBIAS));
 846       VMThread::execute(&bulk_revoke);
 847       if (event.should_commit()) {
 848         post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
 849       }
 850       return;
 851     }
 852   }
 853 }
 854 
 855 // All objects in objs should be locked by biaser
 856 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
 857   bool clean_my_cache = false;
 858   for (int i = 0; i < objs->length(); i++) {
 859     oop obj = (objs->at(i))();
 860     markWord mark = obj->mark();
 861     if (mark.has_bias_pattern()) {
 862       walk_stack_and_revoke(obj, biaser);
 863       clean_my_cache = true;
 864     }
 865   }
 866   if (clean_my_cache) {
 867     clean_up_cached_monitor_info(biaser);
 868   }
 869 }
 870 
 871 
 872 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
 873   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
 874   oop obj = h_obj();
 875   HeuristicsResult heuristics = update_heuristics(obj);
 876   if (heuristics == HR_SINGLE_REVOKE) {
 877     JavaThread* biased_locker = NULL;
 878     single_revoke_at_safepoint(obj, false, NULL, &biased_locker);
 879     if (biased_locker) {
 880       clean_up_cached_monitor_info(biased_locker);
 881     }
 882   } else if ((heuristics == HR_BULK_REBIAS) ||
 883              (heuristics == HR_BULK_REVOKE)) {
 884     bulk_revoke_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), NULL);
 885     clean_up_cached_monitor_info();
 886   }
 887 }
 888 
 889 
 890 void BiasedLocking::preserve_marks() {
 891   if (!UseBiasedLocking)
 892     return;
 893 
 894   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
 895 
 896   assert(_preserved_oop_stack  == NULL, "double initialization");
 897   assert(_preserved_mark_stack == NULL, "double initialization");
 898 
 899   // In order to reduce the number of mark words preserved during GC
 900   // due to the presence of biased locking, we reinitialize most mark
 901   // words to the class's prototype during GC -- even those which have
 902   // a currently valid bias owner. One important situation where we
 903   // must not clobber a bias is when a biased object is currently
 904   // locked. To handle this case we iterate over the currently-locked
 905   // monitors in a prepass and, if they are biased, preserve their
 906   // mark words here. This should be a relatively small set of objects
 907   // especially compared to the number of objects in the heap.
 908   _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markWord>(10, true);
 909   _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
 910 
 911   ResourceMark rm;
 912   Thread* cur = Thread::current();
 913   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
 914     if (thread->has_last_Java_frame()) {
 915       RegisterMap rm(thread);
 916       for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
 917         GrowableArray<MonitorInfo*> *monitors = vf->monitors();
 918         if (monitors != NULL) {
 919           int len = monitors->length();
 920           // Walk monitors youngest to oldest
 921           for (int i = len - 1; i >= 0; i--) {
 922             MonitorInfo* mon_info = monitors->at(i);
 923             if (mon_info->owner_is_scalar_replaced()) continue;
 924             oop owner = mon_info->owner();
 925             if (owner != NULL) {
 926               markWord mark = owner->mark();
 927               if (mark.has_bias_pattern()) {
 928                 _preserved_oop_stack->push(Handle(cur, owner));
 929                 _preserved_mark_stack->push(mark);
 930               }
 931             }
 932           }
 933         }
 934       }
 935     }
 936   }
 937 }
 938 
 939 
 940 void BiasedLocking::restore_marks() {
 941   if (!UseBiasedLocking)
 942     return;
 943 
 944   assert(_preserved_oop_stack  != NULL, "double free");
 945   assert(_preserved_mark_stack != NULL, "double free");
 946 
 947   int len = _preserved_oop_stack->length();
 948   for (int i = 0; i < len; i++) {
 949     Handle owner = _preserved_oop_stack->at(i);
 950     markWord mark = _preserved_mark_stack->at(i);
 951     owner->set_mark(mark);
 952   }
 953 
 954   delete _preserved_oop_stack;
 955   _preserved_oop_stack = NULL;
 956   delete _preserved_mark_stack;
 957   _preserved_mark_stack = NULL;
 958 }
 959 
 960 
 961 int* BiasedLocking::total_entry_count_addr()                   { return _counters.total_entry_count_addr(); }
 962 int* BiasedLocking::biased_lock_entry_count_addr()             { return _counters.biased_lock_entry_count_addr(); }
 963 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
 964 int* BiasedLocking::rebiased_lock_entry_count_addr()           { return _counters.rebiased_lock_entry_count_addr(); }
 965 int* BiasedLocking::revoked_lock_entry_count_addr()            { return _counters.revoked_lock_entry_count_addr(); }
 966 int* BiasedLocking::handshakes_count_addr()                    { return _counters.handshakes_count_addr(); }
 967 int* BiasedLocking::fast_path_entry_count_addr()               { return _counters.fast_path_entry_count_addr(); }
 968 int* BiasedLocking::slow_path_entry_count_addr()               { return _counters.slow_path_entry_count_addr(); }
 969 
 970 
 971 // BiasedLockingCounters
 972 
 973 int BiasedLockingCounters::slow_path_entry_count() const {
 974   if (_slow_path_entry_count != 0) {
 975     return _slow_path_entry_count;
 976   }
 977   int sum = _biased_lock_entry_count   + _anonymously_biased_lock_entry_count +
 978             _rebiased_lock_entry_count + _revoked_lock_entry_count +
 979             _fast_path_entry_count;
 980 
 981   return _total_entry_count - sum;
 982 }
 983 
 984 void BiasedLockingCounters::print_on(outputStream* st) const {
 985   tty->print_cr("# total entries: %d", _total_entry_count);
 986   tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
 987   tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
 988   tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
 989   tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
 990   tty->print_cr("# handshakes entries: %d", _handshakes_count);
 991   tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
 992   tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
 993 }
 994 
 995 void BiasedLockingCounters::print() const { print_on(tty); }
--- EOF ---