/*

 * Copyright 2005-2009 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 *

 */

# include "incls/_precompiled.incl"

# include "incls/_biasedLocking.cpp.incl"

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(klassOop k) {

  Klass::cast(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 system dictionary enabling biased locking for all

    // currently loaded classes

    SystemDictionary::classes_do(enable_biased_locking);

    // Indicate that future instances should enable it as well

    _biased_locking_enabled = true;

    if (TraceBiasedLocking) {

      tty->print_cr("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->owner_is_scalar_replaced()) 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 (TraceBiasedLocking) {

      ResourceMark rm;

      tty->print_cr("  (Skipping revocation of object of type %s because it's no longer biased)",

                    Klass::cast(obj->klass())->external_name());

    }

    return BiasedLocking::NOT_BIASED;

  }

  int age = mark->age();

  markOop   biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);

  markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);

  if (TraceBiasedLocking && (Verbose || !is_bulk)) {

    ResourceMark rm;

    tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT,

                  (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(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);

    }

    if (TraceBiasedLocking && (Verbose || !is_bulk)) {

      tty->print_cr("  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);

    }

    if (TraceBiasedLocking && (Verbose || !is_bulk)) {

      tty->print_cr("  Revoked bias of object biased toward dead thread");

    }

    return BiasedLocking::BIAS_REVOKED;

  }

  // 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) {

      if (TraceBiasedLocking && Verbose) {

        tty->print_cr("   mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",

                      (intptr_t) mon_info->owner(),

                      (intptr_t) 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 {

      if (TraceBiasedLocking && Verbose) {

        tty->print_cr("   mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",

                      (intptr_t) mon_info->owner(),

                      (intptr_t) 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

    obj->set_mark(markOopDesc::encode(highest_lock));

    assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");

    if (TraceBiasedLocking && (Verbose || !is_bulk)) {

      tty->print_cr("  Revoked bias of currently-locked object");

    }

  } else {

    if (TraceBiasedLocking && (Verbose || !is_bulk)) {

      tty->print_cr("  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->blueprint();

  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");

  if (TraceBiasedLocking) {

    tty->print_cr("* Beginning bulk revocation (kind == %s) because of object "

                  INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",

                  (bulk_rebias ? "rebias" : "revoke"),

                  (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name());

  }

  jlong cur_time = os::javaTimeMillis();

  o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time);

  klassOop k_o = o->klass();

  Klass* klass = Klass::cast(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 (TraceBiasedLocking) {

      ResourceMark rm;

      tty->print_cr("* 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);

  }

  if (TraceBiasedLocking) {

    tty->print_cr("* 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;

    if (TraceBiasedLocking) {

      tty->print_cr("  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) {

      if (TraceBiasedLocking) {

        tty->print_cr("Revoking bias with potentially per-thread safepoint:");

      }

      _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);

      clean_up_cached_monitor_info();

      return;

    } else {

      if (TraceBiasedLocking) {

        tty->print_cr("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.