src/thread-inl.h

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_SRC_THREAD_INL_H_
#define ART_SRC_THREAD_INL_H_

#include "thread.h"

#include "base/mutex-inl.h"
#include "cutils/atomic-inline.h"

namespace art {

inline ThreadState Thread::SetState(ThreadState new_state) {
  // Cannot use this code to change into Runnable as changing to Runnable should fail if
  // old_state_and_flags.suspend_request is true.
  DCHECK_NE(new_state, kRunnable);
  DCHECK_EQ(this, Thread::Current());
  union StateAndFlags old_state_and_flags = state_and_flags_;
  state_and_flags_.as_struct.state = new_state;
  return static_cast<ThreadState>(old_state_and_flags.as_struct.state);
}

inline void Thread::AssertThreadSuspensionIsAllowable(bool check_locks) const {
#ifdef NDEBUG
  UNUSED(check_locks);  // Keep GCC happy about unused parameters.
#else
  CHECK_EQ(0u, no_thread_suspension_) << last_no_thread_suspension_cause_;
  if (check_locks) {
    bool bad_mutexes_held = false;
    for (int i = kLockLevelCount - 1; i >= 0; --i) {
      // We expect no locks except the mutator_lock_.
      if (i != kMutatorLock) {
        BaseMutex* held_mutex = GetHeldMutex(static_cast<LockLevel>(i));
        if (held_mutex != NULL) {
          LOG(ERROR) << "holding \"" << held_mutex->GetName()
                  << "\" at point where thread suspension is expected";
          bad_mutexes_held = true;
        }
      }
    }
    CHECK(!bad_mutexes_held);
  }
#endif
}

inline void Thread::TransitionFromRunnableToSuspended(ThreadState new_state) {
  AssertThreadSuspensionIsAllowable();
  DCHECK_NE(new_state, kRunnable);
  DCHECK_EQ(this, Thread::Current());
  // Change to non-runnable state, thereby appearing suspended to the system.
  DCHECK_EQ(GetState(), kRunnable);
  union StateAndFlags old_state_and_flags;
  union StateAndFlags new_state_and_flags;
  do {
    old_state_and_flags = state_and_flags_;
    // Copy over flags and try to clear the checkpoint bit if it is set.
    new_state_and_flags.as_struct.flags = old_state_and_flags.as_struct.flags & ~kCheckpointRequest;
    new_state_and_flags.as_struct.state = new_state;
    // CAS the value without a memory barrier, that will occur in the unlock below.
  } while (UNLIKELY(android_atomic_cas(old_state_and_flags.as_int, new_state_and_flags.as_int,
                                       &state_and_flags_.as_int) != 0));
  // If we toggled the checkpoint flag we must have cleared it.
  uint16_t flag_change = new_state_and_flags.as_struct.flags ^ old_state_and_flags.as_struct.flags;
  if (UNLIKELY((flag_change & kCheckpointRequest) != 0)) {
    RunCheckpointFunction();
  }
  // Release share on mutator_lock_.
  Locks::mutator_lock_->SharedUnlock(this);
}

inline ThreadState Thread::TransitionFromSuspendedToRunnable() {
  bool done = false;
  union StateAndFlags old_state_and_flags = state_and_flags_;
  int16_t old_state = old_state_and_flags.as_struct.state;
  DCHECK_NE(static_cast<ThreadState>(old_state), kRunnable);
  do {
    Locks::mutator_lock_->AssertNotHeld(this);  // Otherwise we starve GC..
    old_state_and_flags = state_and_flags_;
    DCHECK_EQ(old_state_and_flags.as_struct.state, old_state);
    if (UNLIKELY((old_state_and_flags.as_struct.flags & kSuspendRequest) != 0)) {
      // Wait while our suspend count is non-zero.
      MutexLock mu(this, *Locks::thread_suspend_count_lock_);
      old_state_and_flags = state_and_flags_;
      DCHECK_EQ(old_state_and_flags.as_struct.state, old_state);
      while ((old_state_and_flags.as_struct.flags & kSuspendRequest) != 0) {
        // Re-check when Thread::resume_cond_ is notified.
        Thread::resume_cond_->Wait(this);
        old_state_and_flags = state_and_flags_;
        DCHECK_EQ(old_state_and_flags.as_struct.state, old_state);
      }
      DCHECK_EQ(GetSuspendCount(), 0);
    }
    // Re-acquire shared mutator_lock_ access.
    Locks::mutator_lock_->SharedLock(this);
    // Atomically change from suspended to runnable if no suspend request pending.
    old_state_and_flags = state_and_flags_;
    DCHECK_EQ(old_state_and_flags.as_struct.state, old_state);
    if (LIKELY((old_state_and_flags.as_struct.flags & kSuspendRequest) == 0)) {
      union StateAndFlags new_state_and_flags = old_state_and_flags;
      new_state_and_flags.as_struct.state = kRunnable;
      // CAS the value without a memory barrier, that occurred in the lock above.
      done = android_atomic_cas(old_state_and_flags.as_int, new_state_and_flags.as_int,
                                &state_and_flags_.as_int) == 0;
    }
    if (UNLIKELY(!done)) {
      // Failed to transition to Runnable. Release shared mutator_lock_ access and try again.
      Locks::mutator_lock_->SharedUnlock(this);
    }
  } while (UNLIKELY(!done));
  return static_cast<ThreadState>(old_state);
}

}  // namespace art

#endif  // ART_SRC_THREAD_INL_H_