1 /*
   2  * Copyright (c) 2005, 2018, 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/vm_operations.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 
 503 public:
 504   VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
 505     : _obj(obj)
 506     , _objs(NULL)
 507     , _requesting_thread(requesting_thread)
 508     , _status_code(BiasedLocking::NOT_BIASED)
 509     , _biased_locker_id(0) {}
 510 
 511   VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
 512     : _obj(NULL)
 513     , _objs(objs)
 514     , _requesting_thread(requesting_thread)
 515     , _status_code(BiasedLocking::NOT_BIASED)
 516     , _biased_locker_id(0) {}
 517 
 518   virtual VMOp_Type type() const { return VMOp_RevokeBias; }
 519 
 520   virtual bool doit_prologue() {
 521     // Verify that there is actual work to do since the callers just
 522     // give us locked object(s). If we don't find any biased objects
 523     // there is nothing to do and we avoid a safepoint.
 524     if (_obj != NULL) {
 525       markOop mark = (*_obj)()->mark();
 526       if (mark->has_bias_pattern()) {
 527         return true;
 528       }
 529     } else {
 530       for ( int i = 0 ; i < _objs->length(); i++ ) {
 531         markOop mark = (_objs->at(i))()->mark();
 532         if (mark->has_bias_pattern()) {
 533           return true;
 534         }
 535       }
 536     }
 537     return false;
 538   }
 539 
 540   virtual void doit() {
 541     if (_obj != NULL) {
 542       log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
 543       JavaThread* biased_locker = NULL;
 544       _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
 545       if (biased_locker != NULL) {
 546         _biased_locker_id = JFR_THREAD_ID(biased_locker);
 547       }
 548       clean_up_cached_monitor_info();
 549       return;
 550     } else {
 551       log_info(biasedlocking)("Revoking bias with global safepoint:");
 552       BiasedLocking::revoke_at_safepoint(_objs);
 553     }
 554   }
 555 
 556   BiasedLocking::Condition status_code() const {
 557     return _status_code;
 558   }
 559 
 560   traceid biased_locker() const {
 561     return _biased_locker_id;
 562   }
 563 };
 564 
 565 
 566 class VM_BulkRevokeBias : public VM_RevokeBias {
 567 private:
 568   bool _bulk_rebias;
 569   bool _attempt_rebias_of_object;
 570 
 571 public:
 572   VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
 573                     bool bulk_rebias,
 574                     bool attempt_rebias_of_object)
 575     : VM_RevokeBias(obj, requesting_thread)
 576     , _bulk_rebias(bulk_rebias)
 577     , _attempt_rebias_of_object(attempt_rebias_of_object) {}
 578 
 579   virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
 580   virtual bool doit_prologue()   { return true; }
 581 
 582   virtual void doit() {
 583     _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
 584     clean_up_cached_monitor_info();
 585   }
 586 };
 587 
 588 template <typename E>
 589 static void set_safepoint_id(E* event) {
 590   assert(event != NULL, "invariant");
 591   // Subtract 1 to match the id of events committed inside the safepoint
 592   event->set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
 593 }
 594 
 595 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
 596   assert(event != NULL, "invariant");
 597   assert(k != NULL, "invariant");
 598   assert(event->should_commit(), "invariant");
 599   event->set_lockClass(k);
 600   event->commit();
 601 }
 602 
 603 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, VM_RevokeBias* revoke) {
 604   assert(event != NULL, "invariant");
 605   assert(k != NULL, "invariant");
 606   assert(revoke != NULL, "invariant");
 607   assert(event->should_commit(), "invariant");
 608   event->set_lockClass(k);
 609   set_safepoint_id(event);
 610   event->set_previousOwner(revoke->biased_locker());
 611   event->commit();
 612 }
 613 
 614 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, bool disabled_bias) {
 615   assert(event != NULL, "invariant");
 616   assert(k != NULL, "invariant");
 617   assert(event->should_commit(), "invariant");
 618   event->set_revokedClass(k);
 619   event->set_disableBiasing(disabled_bias);
 620   set_safepoint_id(event);
 621   event->commit();
 622 }
 623 
 624 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
 625   assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
 626 
 627   // We can revoke the biases of anonymously-biased objects
 628   // efficiently enough that we should not cause these revocations to
 629   // update the heuristics because doing so may cause unwanted bulk
 630   // revocations (which are expensive) to occur.
 631   markOop mark = obj->mark();
 632   if (mark->is_biased_anonymously() && !attempt_rebias) {
 633     // We are probably trying to revoke the bias of this object due to
 634     // an identity hash code computation. Try to revoke the bias
 635     // without a safepoint. This is possible if we can successfully
 636     // compare-and-exchange an unbiased header into the mark word of
 637     // the object, meaning that no other thread has raced to acquire
 638     // the bias of the object.
 639     markOop biased_value       = mark;
 640     markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
 641     markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
 642     if (res_mark == biased_value) {
 643       return BIAS_REVOKED;
 644     }
 645   } else if (mark->has_bias_pattern()) {
 646     Klass* k = obj->klass();
 647     markOop prototype_header = k->prototype_header();
 648     if (!prototype_header->has_bias_pattern()) {
 649       // This object has a stale bias from before the bulk revocation
 650       // for this data type occurred. It's pointless to update the
 651       // heuristics at this point so simply update the header with a
 652       // CAS. If we fail this race, the object's bias has been revoked
 653       // by another thread so we simply return and let the caller deal
 654       // with it.
 655       markOop biased_value       = mark;
 656       markOop res_mark = obj->cas_set_mark(prototype_header, mark);
 657       assert(!obj->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
 658       return BIAS_REVOKED;
 659     } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
 660       // The epoch of this biasing has expired indicating that the
 661       // object is effectively unbiased. Depending on whether we need
 662       // to rebias or revoke the bias of this object we can do it
 663       // efficiently enough with a CAS that we shouldn't update the
 664       // heuristics. This is normally done in the assembly code but we
 665       // can reach this point due to various points in the runtime
 666       // needing to revoke biases.
 667       if (attempt_rebias) {
 668         assert(THREAD->is_Java_thread(), "");
 669         markOop biased_value       = mark;
 670         markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
 671         markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
 672         if (res_mark == biased_value) {
 673           return BIAS_REVOKED_AND_REBIASED;
 674         }
 675       } else {
 676         markOop biased_value       = mark;
 677         markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
 678         markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
 679         if (res_mark == biased_value) {
 680           return BIAS_REVOKED;
 681         }
 682       }
 683     }
 684   }
 685 
 686   HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
 687   if (heuristics == HR_NOT_BIASED) {
 688     return NOT_BIASED;
 689   } else if (heuristics == HR_SINGLE_REVOKE) {
 690     Klass *k = obj->klass();
 691     markOop prototype_header = k->prototype_header();
 692     if (mark->biased_locker() == THREAD &&
 693         prototype_header->bias_epoch() == mark->bias_epoch()) {
 694       // A thread is trying to revoke the bias of an object biased
 695       // toward it, again likely due to an identity hash code
 696       // computation. We can again avoid a safepoint in this case
 697       // since we are only going to walk our own stack. There are no
 698       // races with revocations occurring in other threads because we
 699       // reach no safepoints in the revocation path.
 700       // Also check the epoch because even if threads match, another thread
 701       // can come in with a CAS to steal the bias of an object that has a
 702       // stale epoch.
 703       ResourceMark rm;
 704       log_info(biasedlocking)("Revoking bias by walking my own stack:");
 705       EventBiasedLockSelfRevocation event;
 706       BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
 707       ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
 708       assert(cond == BIAS_REVOKED, "why not?");
 709       if (event.should_commit()) {
 710         post_self_revocation_event(&event, k);
 711       }
 712       return cond;
 713     } else {
 714       EventBiasedLockRevocation event;
 715       VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
 716       VMThread::execute(&revoke);
 717       if (event.should_commit() && revoke.status_code() != NOT_BIASED) {
 718         post_revocation_event(&event, k, &revoke);
 719       }
 720       return revoke.status_code();
 721     }
 722   }
 723 
 724   assert((heuristics == HR_BULK_REVOKE) ||
 725          (heuristics == HR_BULK_REBIAS), "?");
 726   EventBiasedLockClassRevocation event;
 727   VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
 728                                 (heuristics == HR_BULK_REBIAS),
 729                                 attempt_rebias);
 730   VMThread::execute(&bulk_revoke);
 731   if (event.should_commit()) {
 732     post_class_revocation_event(&event, obj->klass(), heuristics != HR_BULK_REBIAS);
 733   }
 734   return bulk_revoke.status_code();
 735 }
 736 
 737 
 738 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
 739   assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
 740   if (objs->length() == 0) {
 741     return;
 742   }
 743   VM_RevokeBias revoke(objs, JavaThread::current());
 744   VMThread::execute(&revoke);
 745 }
 746 
 747 
 748 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
 749   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
 750   oop obj = h_obj();
 751   HeuristicsResult heuristics = update_heuristics(obj, false);
 752   if (heuristics == HR_SINGLE_REVOKE) {
 753     revoke_bias(obj, false, false, NULL, NULL);
 754   } else if ((heuristics == HR_BULK_REBIAS) ||
 755              (heuristics == HR_BULK_REVOKE)) {
 756     bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
 757   }
 758   clean_up_cached_monitor_info();
 759 }
 760 
 761 
 762 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
 763   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
 764   int len = objs->length();
 765   for (int i = 0; i < len; i++) {
 766     oop obj = (objs->at(i))();
 767     HeuristicsResult heuristics = update_heuristics(obj, false);
 768     if (heuristics == HR_SINGLE_REVOKE) {
 769       revoke_bias(obj, false, false, NULL, NULL);
 770     } else if ((heuristics == HR_BULK_REBIAS) ||
 771                (heuristics == HR_BULK_REVOKE)) {
 772       bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
 773     }
 774   }
 775   clean_up_cached_monitor_info();
 776 }
 777 
 778 
 779 void BiasedLocking::preserve_marks() {
 780   if (!UseBiasedLocking)
 781     return;
 782 
 783   assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
 784 
 785   assert(_preserved_oop_stack  == NULL, "double initialization");
 786   assert(_preserved_mark_stack == NULL, "double initialization");
 787 
 788   // In order to reduce the number of mark words preserved during GC
 789   // due to the presence of biased locking, we reinitialize most mark
 790   // words to the class's prototype during GC -- even those which have
 791   // a currently valid bias owner. One important situation where we
 792   // must not clobber a bias is when a biased object is currently
 793   // locked. To handle this case we iterate over the currently-locked
 794   // monitors in a prepass and, if they are biased, preserve their
 795   // mark words here. This should be a relatively small set of objects
 796   // especially compared to the number of objects in the heap.
 797   _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
 798   _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
 799 
 800   ResourceMark rm;
 801   Thread* cur = Thread::current();
 802   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
 803     if (thread->has_last_Java_frame()) {
 804       RegisterMap rm(thread);
 805       for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
 806         GrowableArray<MonitorInfo*> *monitors = vf->monitors();
 807         if (monitors != NULL) {
 808           int len = monitors->length();
 809           // Walk monitors youngest to oldest
 810           for (int i = len - 1; i >= 0; i--) {
 811             MonitorInfo* mon_info = monitors->at(i);
 812             if (mon_info->owner_is_scalar_replaced()) continue;
 813             oop owner = mon_info->owner();
 814             if (owner != NULL) {
 815               markOop mark = owner->mark();
 816               if (mark->has_bias_pattern()) {
 817                 _preserved_oop_stack->push(Handle(cur, owner));
 818                 _preserved_mark_stack->push(mark);
 819               }
 820             }
 821           }
 822         }
 823       }
 824     }
 825   }
 826 }
 827 
 828 
 829 void BiasedLocking::restore_marks() {
 830   if (!UseBiasedLocking)
 831     return;
 832 
 833   assert(_preserved_oop_stack  != NULL, "double free");
 834   assert(_preserved_mark_stack != NULL, "double free");
 835 
 836   int len = _preserved_oop_stack->length();
 837   for (int i = 0; i < len; i++) {
 838     Handle owner = _preserved_oop_stack->at(i);
 839     markOop mark = _preserved_mark_stack->at(i);
 840     owner->set_mark(mark);
 841   }
 842 
 843   delete _preserved_oop_stack;
 844   _preserved_oop_stack = NULL;
 845   delete _preserved_mark_stack;
 846   _preserved_mark_stack = NULL;
 847 }
 848 
 849 
 850 int* BiasedLocking::total_entry_count_addr()                   { return _counters.total_entry_count_addr(); }
 851 int* BiasedLocking::biased_lock_entry_count_addr()             { return _counters.biased_lock_entry_count_addr(); }
 852 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
 853 int* BiasedLocking::rebiased_lock_entry_count_addr()           { return _counters.rebiased_lock_entry_count_addr(); }
 854 int* BiasedLocking::revoked_lock_entry_count_addr()            { return _counters.revoked_lock_entry_count_addr(); }
 855 int* BiasedLocking::fast_path_entry_count_addr()               { return _counters.fast_path_entry_count_addr(); }
 856 int* BiasedLocking::slow_path_entry_count_addr()               { return _counters.slow_path_entry_count_addr(); }
 857 
 858 
 859 // BiasedLockingCounters
 860 
 861 int BiasedLockingCounters::slow_path_entry_count() {
 862   if (_slow_path_entry_count != 0) {
 863     return _slow_path_entry_count;
 864   }
 865   int sum = _biased_lock_entry_count   + _anonymously_biased_lock_entry_count +
 866             _rebiased_lock_entry_count + _revoked_lock_entry_count +
 867             _fast_path_entry_count;
 868 
 869   return _total_entry_count - sum;
 870 }
 871 
 872 void BiasedLockingCounters::print_on(outputStream* st) {
 873   tty->print_cr("# total entries: %d", _total_entry_count);
 874   tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
 875   tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
 876   tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
 877   tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
 878   tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
 879   tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
 880 }