ART_Lock

ObjectLock<mirror::Class> lock(self, klass);

template <typename T>
ObjectLock<T>::ObjectLock(Thread* self, Handle<T> object) : self_(self), obj_(object) {
  CHECK(object != nullptr);
  obj_->MonitorEnter(self_);
}

template <typename T>
ObjectLock<T>::~ObjectLock() {
  obj_->MonitorExit(self_);
}

inline mirror::Object* Object::MonitorEnter(Thread* self) {
  return Monitor::MonitorEnter(self, this, /*trylock*/false);
}

mirror::Object* Monitor::MonitorEnter(Thread* self, mirror::Object* obj, bool trylock) {
    StackHandleScope<1> hs(self);
  Handle<mirror::Object> h_obj(hs.NewHandle(obj));
  while (true) {
    // We initially read the lockword with ordinary Java/relaxed semantics. When stronger
    // semantics are needed, we address it below. Since GetLockWord bottoms out to a relaxed load,
    // we can fix it later, in an infrequently executed case, with a fence.
    LockWord lock_word = h_obj->GetLockWord(false);
    switch (lock_word.GetState()) {
      case LockWord::kUnlocked: {
        // No ordering required for preceding lockword read, since we retest.
        LockWord thin_locked(LockWord::FromThinLockId(thread_id, 0, lock_word.GCState()));
        if (h_obj->CasLockWordWeakAcquire(lock_word, thin_locked)) {
          AtraceMonitorLock(self, h_obj.Get(), false /* is_wait */);
          return h_obj.Get();  // Success!
        }
        continue;  // Go again.
      }
      case LockWord::kThinLocked: {
      case LockWord::kFatLocked: {

enum LockState {
  kUnlocked,    // No lock owners.
  kThinLocked,  // Single uncontended owner.
  kFatLocked,   // See associated monitor.
  kHashCode,    // Lock word contains an identity hash.
  kForwardingAddress,  // Lock word contains the forwarding address of an object.
};

  /// @brief  Scoped lock idiom.
  // Acquire the mutex here with a constructor call, then release with
  // the destructor call in accordance with RAII style.
  template<typename _Mutex>
    class lock_guard
    {
    public:
      typedef _Mutex mutex_type;

      explicit lock_guard(mutex_type& __m) : _M_device(__m)
      { _M_device.lock(); }

      lock_guard(mutex_type& __m, adopt_lock_t) : _M_device(__m)
      { } // calling thread owns mutex

      ~lock_guard()
      { _M_device.unlock(); }

      lock_guard(const lock_guard&) = delete;
      lock_guard& operator=(const lock_guard&) = delete;

    private:
      mutex_type&  _M_device;
    };