8187443: Forest Consolidation: Move files to unified layout

Reviewed-by: darcy, ihse

src/hotspot/share/runtime/biasedLocking.cpp

@@ -0,0 +1,809 @@
+/*
+ * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "logging/log.hpp"
+#include "memory/resourceArea.hpp"
+#include "oops/klass.inline.hpp"
+#include "oops/markOop.hpp"
+#include "oops/oop.inline.hpp"
+#include "runtime/atomic.hpp"
+#include "runtime/basicLock.hpp"
+#include "runtime/biasedLocking.hpp"
+#include "runtime/task.hpp"
+#include "runtime/vframe.hpp"
+#include "runtime/vmThread.hpp"
+#include "runtime/vm_operations.hpp"
+
+static bool _biased_locking_enabled = false;
+BiasedLockingCounters BiasedLocking::_counters;
+
+static GrowableArray<Handle>*  _preserved_oop_stack  = NULL;
+static GrowableArray<markOop>* _preserved_mark_stack = NULL;
+
+static void enable_biased_locking(InstanceKlass* k) {
+  k->set_prototype_header(markOopDesc::biased_locking_prototype());
+}
+
+class VM_EnableBiasedLocking: public VM_Operation {
+ private:
+  bool _is_cheap_allocated;
+ public:
+  VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
+  VMOp_Type type() const          { return VMOp_EnableBiasedLocking; }
+  Mode evaluation_mode() const    { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
+  bool is_cheap_allocated() const { return _is_cheap_allocated; }
+
+  void doit() {
+    // Iterate the class loader data dictionaries enabling biased locking for all
+    // currently loaded classes.
+    ClassLoaderDataGraph::dictionary_classes_do(enable_biased_locking);
+    // Indicate that future instances should enable it as well
+    _biased_locking_enabled = true;
+
+    log_info(biasedlocking)("Biased locking enabled");
+  }
+
+  bool allow_nested_vm_operations() const        { return false; }
+};
+
+
+// One-shot PeriodicTask subclass for enabling biased locking
+class EnableBiasedLockingTask : public PeriodicTask {
+ public:
+  EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {}
+
+  virtual void task() {
+    // Use async VM operation to avoid blocking the Watcher thread.
+    // VM Thread will free C heap storage.
+    VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true);
+    VMThread::execute(op);
+
+    // Reclaim our storage and disenroll ourself
+    delete this;
+  }
+};
+
+
+void BiasedLocking::init() {
+  // If biased locking is enabled, schedule a task to fire a few
+  // seconds into the run which turns on biased locking for all
+  // currently loaded classes as well as future ones. This is a
+  // workaround for startup time regressions due to a large number of
+  // safepoints being taken during VM startup for bias revocation.
+  // Ideally we would have a lower cost for individual bias revocation
+  // and not need a mechanism like this.
+  if (UseBiasedLocking) {
+    if (BiasedLockingStartupDelay > 0) {
+      EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
+      task->enroll();
+    } else {
+      VM_EnableBiasedLocking op(false);
+      VMThread::execute(&op);
+    }
+  }
+}
+
+
+bool BiasedLocking::enabled() {
+  return _biased_locking_enabled;
+}
+
+// Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
+static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
+  GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
+  if (info != NULL) {
+    return info;
+  }
+
+  info = new GrowableArray<MonitorInfo*>();
+
+  // It's possible for the thread to not have any Java frames on it,
+  // i.e., if it's the main thread and it's already returned from main()
+  if (thread->has_last_Java_frame()) {
+    RegisterMap rm(thread);
+    for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
+      GrowableArray<MonitorInfo*> *monitors = vf->monitors();
+      if (monitors != NULL) {
+        int len = monitors->length();
+        // Walk monitors youngest to oldest
+        for (int i = len - 1; i >= 0; i--) {
+          MonitorInfo* mon_info = monitors->at(i);
+          if (mon_info->eliminated()) continue;
+          oop owner = mon_info->owner();
+          if (owner != NULL) {
+            info->append(mon_info);
+          }
+        }
+      }
+    }
+  }
+
+  thread->set_cached_monitor_info(info);
+  return info;
+}
+
+static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
+  markOop mark = obj->mark();
+  if (!mark->has_bias_pattern()) {
+    if (log_is_enabled(Info, biasedlocking)) {
+      ResourceMark rm;
+      log_info(biasedlocking)("  (Skipping revocation of object " INTPTR_FORMAT
+                              ", mark " INTPTR_FORMAT ", type %s"
+                              ", requesting thread " INTPTR_FORMAT
+                              " because it's no longer biased)",
+                              p2i((void *)obj), (intptr_t) mark,
+                              obj->klass()->external_name(),
+                              (intptr_t) requesting_thread);
+    }
+    return BiasedLocking::NOT_BIASED;
+  }
+
+  uint age = mark->age();
+  markOop   biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
+  markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
+
+  // Log at "info" level if not bulk, else "trace" level
+  if (!is_bulk) {
+    ResourceMark rm;
+    log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
+                            INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
+                            ", allow rebias %d, requesting thread " INTPTR_FORMAT,
+                            p2i((void *)obj),
+                            (intptr_t) mark,
+                            obj->klass()->external_name(),
+                            (intptr_t) obj->klass()->prototype_header(),
+                            (allow_rebias ? 1 : 0),
+                            (intptr_t) requesting_thread);
+  } else {
+    ResourceMark rm;
+    log_trace(biasedlocking)("Revoking bias of object " INTPTR_FORMAT " , mark "
+                             INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT
+                             " , allow rebias %d , requesting thread " INTPTR_FORMAT,
+                             p2i((void *)obj),
+                             (intptr_t) mark,
+                             obj->klass()->external_name(),
+                             (intptr_t) obj->klass()->prototype_header(),
+                             (allow_rebias ? 1 : 0),
+                             (intptr_t) requesting_thread);
+  }
+
+  JavaThread* biased_thread = mark->biased_locker();
+  if (biased_thread == NULL) {
+    // Object is anonymously biased. We can get here if, for
+    // example, we revoke the bias due to an identity hash code
+    // being computed for an object.
+    if (!allow_rebias) {
+      obj->set_mark(unbiased_prototype);
+    }
+    // Log at "info" level if not bulk, else "trace" level
+    if (!is_bulk) {
+      log_info(biasedlocking)("  Revoked bias of anonymously-biased object");
+    } else {
+      log_trace(biasedlocking)("  Revoked bias of anonymously-biased object");
+    }
+    return BiasedLocking::BIAS_REVOKED;
+  }
+
+  // Handle case where the thread toward which the object was biased has exited
+  bool thread_is_alive = false;
+  if (requesting_thread == biased_thread) {
+    thread_is_alive = true;
+  } else {
+    for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) {
+      if (cur_thread == biased_thread) {
+        thread_is_alive = true;
+        break;
+      }
+    }
+  }
+  if (!thread_is_alive) {
+    if (allow_rebias) {
+      obj->set_mark(biased_prototype);
+    } else {
+      obj->set_mark(unbiased_prototype);
+    }
+    // Log at "info" level if not bulk, else "trace" level
+    if (!is_bulk) {
+      log_info(biasedlocking)("  Revoked bias of object biased toward dead thread ("
+                              PTR_FORMAT ")", p2i(biased_thread));
+    } else {
+      log_trace(biasedlocking)("  Revoked bias of object biased toward dead thread ("
+                               PTR_FORMAT ")", p2i(biased_thread));
+    }
+    return BiasedLocking::BIAS_REVOKED;
+  }
+
+  // Log at "info" level if not bulk, else "trace" level
+  if (!is_bulk) {
+    log_info(biasedlocking)("  Revoked bias of object biased toward live thread ("
+                            PTR_FORMAT ")", p2i(biased_thread));
+  } else {
+    log_trace(biasedlocking)("  Revoked bias of object biased toward live thread ("
+                               PTR_FORMAT ")", p2i(biased_thread));
+  }
+
+  // Thread owning bias is alive.
+  // Check to see whether it currently owns the lock and, if so,
+  // write down the needed displaced headers to the thread's stack.
+  // Otherwise, restore the object's header either to the unlocked
+  // or unbiased state.
+  GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
+  BasicLock* highest_lock = NULL;
+  for (int i = 0; i < cached_monitor_info->length(); i++) {
+    MonitorInfo* mon_info = cached_monitor_info->at(i);
+    if (mon_info->owner() == obj) {
+      log_trace(biasedlocking)("   mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
+                               p2i((void *) mon_info->owner()),
+                               p2i((void *) obj));
+      // Assume recursive case and fix up highest lock later
+      markOop mark = markOopDesc::encode((BasicLock*) NULL);
+      highest_lock = mon_info->lock();
+      highest_lock->set_displaced_header(mark);
+    } else {
+      log_trace(biasedlocking)("   mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
+                               p2i((void *) mon_info->owner()),
+                               p2i((void *) obj));
+    }
+  }
+  if (highest_lock != NULL) {
+    // Fix up highest lock to contain displaced header and point
+    // object at it
+    highest_lock->set_displaced_header(unbiased_prototype);
+    // Reset object header to point to displaced mark.
+    // Must release storing the lock address for platforms without TSO
+    // ordering (e.g. ppc).
+    obj->release_set_mark(markOopDesc::encode(highest_lock));
+    assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
+    // Log at "info" level if not bulk, else "trace" level
+    if (!is_bulk) {
+      log_info(biasedlocking)("  Revoked bias of currently-locked object");
+    } else {
+      log_trace(biasedlocking)("  Revoked bias of currently-locked object");
+    }
+  } else {
+    // Log at "info" level if not bulk, else "trace" level
+    if (!is_bulk) {
+      log_info(biasedlocking)("  Revoked bias of currently-unlocked object");
+    } else {
+      log_trace(biasedlocking)("  Revoked bias of currently-unlocked object");
+    }
+    if (allow_rebias) {
+      obj->set_mark(biased_prototype);
+    } else {
+      // Store the unlocked value into the object's header.
+      obj->set_mark(unbiased_prototype);
+    }
+  }
+
+  return BiasedLocking::BIAS_REVOKED;
+}
+
+
+enum HeuristicsResult {
+  HR_NOT_BIASED    = 1,
+  HR_SINGLE_REVOKE = 2,
+  HR_BULK_REBIAS   = 3,
+  HR_BULK_REVOKE   = 4
+};
+
+
+static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
+  markOop mark = o->mark();
+  if (!mark->has_bias_pattern()) {
+    return HR_NOT_BIASED;
+  }
+
+  // Heuristics to attempt to throttle the number of revocations.
+  // Stages:
+  // 1. Revoke the biases of all objects in the heap of this type,
+  //    but allow rebiasing of those objects if unlocked.
+  // 2. Revoke the biases of all objects in the heap of this type
+  //    and don't allow rebiasing of these objects. Disable
+  //    allocation of objects of that type with the bias bit set.
+  Klass* k = o->klass();
+  jlong cur_time = os::javaTimeMillis();
+  jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
+  int revocation_count = k->biased_lock_revocation_count();
+  if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
+      (revocation_count <  BiasedLockingBulkRevokeThreshold) &&
+      (last_bulk_revocation_time != 0) &&
+      (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
+    // This is the first revocation we've seen in a while of an
+    // object of this type since the last time we performed a bulk
+    // rebiasing operation. The application is allocating objects in
+    // bulk which are biased toward a thread and then handing them
+    // off to another thread. We can cope with this allocation
+    // pattern via the bulk rebiasing mechanism so we reset the
+    // klass's revocation count rather than allow it to increase
+    // monotonically. If we see the need to perform another bulk
+    // rebias operation later, we will, and if subsequently we see
+    // many more revocation operations in a short period of time we
+    // will completely disable biasing for this type.
+    k->set_biased_lock_revocation_count(0);
+    revocation_count = 0;
+  }
+
+  // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
+  if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
+    revocation_count = k->atomic_incr_biased_lock_revocation_count();
+  }
+
+  if (revocation_count == BiasedLockingBulkRevokeThreshold) {
+    return HR_BULK_REVOKE;
+  }
+
+  if (revocation_count == BiasedLockingBulkRebiasThreshold) {
+    return HR_BULK_REBIAS;
+  }
+
+  return HR_SINGLE_REVOKE;
+}
+
+
+static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
+                                                                   bool bulk_rebias,
+                                                                   bool attempt_rebias_of_object,
+                                                                   JavaThread* requesting_thread) {
+  assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
+
+  log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
+                          INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
+                          (bulk_rebias ? "rebias" : "revoke"),
+                          p2i((void *) o),
+                          (intptr_t) o->mark(),
+                          o->klass()->external_name());
+
+  jlong cur_time = os::javaTimeMillis();
+  o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
+
+
+  Klass* k_o = o->klass();
+  Klass* klass = k_o;
+
+  if (bulk_rebias) {
+    // Use the epoch in the klass of the object to implicitly revoke
+    // all biases of objects of this data type and force them to be
+    // reacquired. However, we also need to walk the stacks of all
+    // threads and update the headers of lightweight locked objects
+    // with biases to have the current epoch.
+
+    // If the prototype header doesn't have the bias pattern, don't
+    // try to update the epoch -- assume another VM operation came in
+    // and reset the header to the unbiased state, which will
+    // implicitly cause all existing biases to be revoked
+    if (klass->prototype_header()->has_bias_pattern()) {
+      int prev_epoch = klass->prototype_header()->bias_epoch();
+      klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
+      int cur_epoch = klass->prototype_header()->bias_epoch();
+
+      // Now walk all threads' stacks and adjust epochs of any biased
+      // and locked objects of this data type we encounter
+      for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
+        GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
+        for (int i = 0; i < cached_monitor_info->length(); i++) {
+          MonitorInfo* mon_info = cached_monitor_info->at(i);
+          oop owner = mon_info->owner();
+          markOop mark = owner->mark();
+          if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
+            // We might have encountered this object already in the case of recursive locking
+            assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
+            owner->set_mark(mark->set_bias_epoch(cur_epoch));
+          }
+        }
+      }
+    }
+
+    // At this point we're done. All we have to do is potentially
+    // adjust the header of the given object to revoke its bias.
+    revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
+  } else {
+    if (log_is_enabled(Info, biasedlocking)) {
+      ResourceMark rm;
+      log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
+    }
+
+    // Disable biased locking for this data type. Not only will this
+    // cause future instances to not be biased, but existing biased
+    // instances will notice that this implicitly caused their biases
+    // to be revoked.
+    klass->set_prototype_header(markOopDesc::prototype());
+
+    // Now walk all threads' stacks and forcibly revoke the biases of
+    // any locked and biased objects of this data type we encounter.
+    for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
+      GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
+      for (int i = 0; i < cached_monitor_info->length(); i++) {
+        MonitorInfo* mon_info = cached_monitor_info->at(i);
+        oop owner = mon_info->owner();
+        markOop mark = owner->mark();
+        if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
+          revoke_bias(owner, false, true, requesting_thread);
+        }
+      }
+    }
+
+    // Must force the bias of the passed object to be forcibly revoked
+    // as well to ensure guarantees to callers
+    revoke_bias(o, false, true, requesting_thread);
+  }
+
+  log_info(biasedlocking)("* Ending bulk revocation");
+
+  BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
+
+  if (attempt_rebias_of_object &&
+      o->mark()->has_bias_pattern() &&
+      klass->prototype_header()->has_bias_pattern()) {
+    markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
+                                           klass->prototype_header()->bias_epoch());
+    o->set_mark(new_mark);
+    status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
+    log_info(biasedlocking)("  Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
+  }
+
+  assert(!o->mark()->has_bias_pattern() ||
+         (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
+         "bug in bulk bias revocation");
+
+  return status_code;
+}
+
+
+static void clean_up_cached_monitor_info() {
+  // Walk the thread list clearing out the cached monitors
+  for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
+    thr->set_cached_monitor_info(NULL);
+  }
+}
+
+
+class VM_RevokeBias : public VM_Operation {
+protected:
+  Handle* _obj;
+  GrowableArray<Handle>* _objs;
+  JavaThread* _requesting_thread;
+  BiasedLocking::Condition _status_code;
+
+public:
+  VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
+    : _obj(obj)
+    , _objs(NULL)
+    , _requesting_thread(requesting_thread)
+    , _status_code(BiasedLocking::NOT_BIASED) {}
+
+  VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
+    : _obj(NULL)
+    , _objs(objs)
+    , _requesting_thread(requesting_thread)
+    , _status_code(BiasedLocking::NOT_BIASED) {}
+
+  virtual VMOp_Type type() const { return VMOp_RevokeBias; }
+
+  virtual bool doit_prologue() {
+    // Verify that there is actual work to do since the callers just
+    // give us locked object(s). If we don't find any biased objects
+    // there is nothing to do and we avoid a safepoint.
+    if (_obj != NULL) {
+      markOop mark = (*_obj)()->mark();
+      if (mark->has_bias_pattern()) {
+        return true;
+      }
+    } else {
+      for ( int i = 0 ; i < _objs->length(); i++ ) {
+        markOop mark = (_objs->at(i))()->mark();
+        if (mark->has_bias_pattern()) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  virtual void doit() {
+    if (_obj != NULL) {
+      log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
+      _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
+      clean_up_cached_monitor_info();
+      return;
+    } else {
+      log_info(biasedlocking)("Revoking bias with global safepoint:");
+      BiasedLocking::revoke_at_safepoint(_objs);
+    }
+  }
+
+  BiasedLocking::Condition status_code() const {
+    return _status_code;
+  }
+};
+
+
+class VM_BulkRevokeBias : public VM_RevokeBias {
+private:
+  bool _bulk_rebias;
+  bool _attempt_rebias_of_object;
+
+public:
+  VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
+                    bool bulk_rebias,
+                    bool attempt_rebias_of_object)
+    : VM_RevokeBias(obj, requesting_thread)
+    , _bulk_rebias(bulk_rebias)
+    , _attempt_rebias_of_object(attempt_rebias_of_object) {}
+
+  virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
+  virtual bool doit_prologue()   { return true; }
+
+  virtual void doit() {
+    _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
+    clean_up_cached_monitor_info();
+  }
+};
+
+
+BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
+  assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
+
+  // We can revoke the biases of anonymously-biased objects
+  // efficiently enough that we should not cause these revocations to
+  // update the heuristics because doing so may cause unwanted bulk
+  // revocations (which are expensive) to occur.
+  markOop mark = obj->mark();
+  if (mark->is_biased_anonymously() && !attempt_rebias) {
+    // We are probably trying to revoke the bias of this object due to
+    // an identity hash code computation. Try to revoke the bias
+    // without a safepoint. This is possible if we can successfully
+    // compare-and-exchange an unbiased header into the mark word of
+    // the object, meaning that no other thread has raced to acquire
+    // the bias of the object.
+    markOop biased_value       = mark;
+    markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
+    markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
+    if (res_mark == biased_value) {
+      return BIAS_REVOKED;
+    }
+  } else if (mark->has_bias_pattern()) {
+    Klass* k = obj->klass();
+    markOop prototype_header = k->prototype_header();
+    if (!prototype_header->has_bias_pattern()) {
+      // This object has a stale bias from before the bulk revocation
+      // for this data type occurred. It's pointless to update the
+      // heuristics at this point so simply update the header with a
+      // CAS. If we fail this race, the object's bias has been revoked
+      // by another thread so we simply return and let the caller deal
+      // with it.
+      markOop biased_value       = mark;
+      markOop res_mark = obj->cas_set_mark(prototype_header, mark);
+      assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked");
+      return BIAS_REVOKED;
+    } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
+      // The epoch of this biasing has expired indicating that the
+      // object is effectively unbiased. Depending on whether we need
+      // to rebias or revoke the bias of this object we can do it
+      // efficiently enough with a CAS that we shouldn't update the
+      // heuristics. This is normally done in the assembly code but we
+      // can reach this point due to various points in the runtime
+      // needing to revoke biases.
+      if (attempt_rebias) {
+        assert(THREAD->is_Java_thread(), "");
+        markOop biased_value       = mark;
+        markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
+        markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
+        if (res_mark == biased_value) {
+          return BIAS_REVOKED_AND_REBIASED;
+        }
+      } else {
+        markOop biased_value       = mark;
+        markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
+        markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
+        if (res_mark == biased_value) {
+          return BIAS_REVOKED;
+        }
+      }
+    }
+  }
+
+  HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
+  if (heuristics == HR_NOT_BIASED) {
+    return NOT_BIASED;
+  } else if (heuristics == HR_SINGLE_REVOKE) {
+    Klass *k = obj->klass();
+    markOop prototype_header = k->prototype_header();
+    if (mark->biased_locker() == THREAD &&
+        prototype_header->bias_epoch() == mark->bias_epoch()) {
+      // A thread is trying to revoke the bias of an object biased
+      // toward it, again likely due to an identity hash code
+      // computation. We can again avoid a safepoint in this case
+      // since we are only going to walk our own stack. There are no
+      // races with revocations occurring in other threads because we
+      // reach no safepoints in the revocation path.
+      // Also check the epoch because even if threads match, another thread
+      // can come in with a CAS to steal the bias of an object that has a
+      // stale epoch.
+      ResourceMark rm;
+      log_info(biasedlocking)("Revoking bias by walking my own stack:");
+      BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
+      ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
+      assert(cond == BIAS_REVOKED, "why not?");
+      return cond;
+    } else {
+      VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
+      VMThread::execute(&revoke);
+      return revoke.status_code();
+    }
+  }
+
+  assert((heuristics == HR_BULK_REVOKE) ||
+         (heuristics == HR_BULK_REBIAS), "?");
+  VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
+                                (heuristics == HR_BULK_REBIAS),
+                                attempt_rebias);
+  VMThread::execute(&bulk_revoke);
+  return bulk_revoke.status_code();
+}
+
+
+void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
+  assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
+  if (objs->length() == 0) {
+    return;
+  }
+  VM_RevokeBias revoke(objs, JavaThread::current());
+  VMThread::execute(&revoke);
+}
+
+
+void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
+  assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
+  oop obj = h_obj();
+  HeuristicsResult heuristics = update_heuristics(obj, false);
+  if (heuristics == HR_SINGLE_REVOKE) {
+    revoke_bias(obj, false, false, NULL);
+  } else if ((heuristics == HR_BULK_REBIAS) ||
+             (heuristics == HR_BULK_REVOKE)) {
+    bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
+  }
+  clean_up_cached_monitor_info();
+}
+
+
+void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
+  assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
+  int len = objs->length();
+  for (int i = 0; i < len; i++) {
+    oop obj = (objs->at(i))();
+    HeuristicsResult heuristics = update_heuristics(obj, false);
+    if (heuristics == HR_SINGLE_REVOKE) {
+      revoke_bias(obj, false, false, NULL);
+    } else if ((heuristics == HR_BULK_REBIAS) ||
+               (heuristics == HR_BULK_REVOKE)) {
+      bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
+    }
+  }
+  clean_up_cached_monitor_info();
+}
+
+
+void BiasedLocking::preserve_marks() {
+  if (!UseBiasedLocking)
+    return;
+
+  assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
+
+  assert(_preserved_oop_stack  == NULL, "double initialization");
+  assert(_preserved_mark_stack == NULL, "double initialization");
+
+  // In order to reduce the number of mark words preserved during GC
+  // due to the presence of biased locking, we reinitialize most mark
+  // words to the class's prototype during GC -- even those which have
+  // a currently valid bias owner. One important situation where we
+  // must not clobber a bias is when a biased object is currently
+  // locked. To handle this case we iterate over the currently-locked
+  // monitors in a prepass and, if they are biased, preserve their
+  // mark words here. This should be a relatively small set of objects
+  // especially compared to the number of objects in the heap.
+  _preserved_mark_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<markOop>(10, true);
+  _preserved_oop_stack = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<Handle>(10, true);
+
+  ResourceMark rm;
+  Thread* cur = Thread::current();
+  for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
+    if (thread->has_last_Java_frame()) {
+      RegisterMap rm(thread);
+      for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
+        GrowableArray<MonitorInfo*> *monitors = vf->monitors();
+        if (monitors != NULL) {
+          int len = monitors->length();
+          // Walk monitors youngest to oldest
+          for (int i = len - 1; i >= 0; i--) {
+            MonitorInfo* mon_info = monitors->at(i);
+            if (mon_info->owner_is_scalar_replaced()) continue;
+            oop owner = mon_info->owner();
+            if (owner != NULL) {
+              markOop mark = owner->mark();
+              if (mark->has_bias_pattern()) {
+                _preserved_oop_stack->push(Handle(cur, owner));
+                _preserved_mark_stack->push(mark);
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+
+
+void BiasedLocking::restore_marks() {
+  if (!UseBiasedLocking)
+    return;
+
+  assert(_preserved_oop_stack  != NULL, "double free");
+  assert(_preserved_mark_stack != NULL, "double free");
+
+  int len = _preserved_oop_stack->length();
+  for (int i = 0; i < len; i++) {
+    Handle owner = _preserved_oop_stack->at(i);
+    markOop mark = _preserved_mark_stack->at(i);
+    owner->set_mark(mark);
+  }
+
+  delete _preserved_oop_stack;
+  _preserved_oop_stack = NULL;
+  delete _preserved_mark_stack;
+  _preserved_mark_stack = NULL;
+}
+
+
+int* BiasedLocking::total_entry_count_addr()                   { return _counters.total_entry_count_addr(); }
+int* BiasedLocking::biased_lock_entry_count_addr()             { return _counters.biased_lock_entry_count_addr(); }
+int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
+int* BiasedLocking::rebiased_lock_entry_count_addr()           { return _counters.rebiased_lock_entry_count_addr(); }
+int* BiasedLocking::revoked_lock_entry_count_addr()            { return _counters.revoked_lock_entry_count_addr(); }
+int* BiasedLocking::fast_path_entry_count_addr()               { return _counters.fast_path_entry_count_addr(); }
+int* BiasedLocking::slow_path_entry_count_addr()               { return _counters.slow_path_entry_count_addr(); }
+
+
+// BiasedLockingCounters
+
+int BiasedLockingCounters::slow_path_entry_count() {
+  if (_slow_path_entry_count != 0) {
+    return _slow_path_entry_count;
+  }
+  int sum = _biased_lock_entry_count   + _anonymously_biased_lock_entry_count +
+            _rebiased_lock_entry_count + _revoked_lock_entry_count +
+            _fast_path_entry_count;
+
+  return _total_entry_count - sum;
+}
+
+void BiasedLockingCounters::print_on(outputStream* st) {
+  tty->print_cr("# total entries: %d", _total_entry_count);
+  tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
+  tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
+  tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
+  tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
+  tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
+  tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
+}