src/base/mutex-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_BASE_MUTEX_INL_H_
#define ART_SRC_BASE_MUTEX_INL_H_

#include "mutex.h"

#include "cutils/atomic-inline.h"
#include "runtime.h"
#include "thread.h"

namespace art {

#define CHECK_MUTEX_CALL(call, args) CHECK_PTHREAD_CALL(call, args, name_)

#if ART_USE_FUTEXES
#include "linux/futex.h"
#include "sys/syscall.h"
#ifndef SYS_futex
#define SYS_futex __NR_futex
#endif
static inline int futex(volatile int *uaddr, int op, int val, const struct timespec *timeout, volatile int *uaddr2, int val3) {
  return syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3);
}
#endif  // ART_USE_FUTEXES

class ScopedContentionRecorder {
 public:
  ScopedContentionRecorder(BaseMutex* mutex, uint64_t blocked_tid, uint64_t owner_tid) :
      mutex_(mutex), blocked_tid_(blocked_tid), owner_tid_(owner_tid),
      start_milli_time_(MilliTime()) {
  }

  ~ScopedContentionRecorder() {
    uint64_t end_milli_time = MilliTime();
    mutex_->RecordContention(blocked_tid_, owner_tid_, end_milli_time - start_milli_time_);
  }

 private:
  BaseMutex* const mutex_;
  uint64_t blocked_tid_;
  uint64_t owner_tid_;
  const uint64_t start_milli_time_;
};

static inline uint64_t SafeGetTid(const Thread* self) {
  if (self != NULL) {
    return static_cast<uint64_t>(self->GetTid());
  } else {
    return static_cast<uint64_t>(GetTid());
  }
}

static inline void CheckUnattachedThread(LockLevel level) NO_THREAD_SAFETY_ANALYSIS {
  // The check below enumerates the cases where we expect not to be able to sanity check locks
  // on a thread. Lock checking is disabled to avoid deadlock when checking shutdown lock.
  // TODO: tighten this check.
  if (kDebugLocking) {
    Runtime* runtime = Runtime::Current();
    CHECK(runtime == NULL || !runtime->IsStarted() || runtime->IsShuttingDown() ||
          level == kDefaultMutexLevel  || level == kRuntimeShutdownLock ||
          level == kThreadListLock || level == kLoggingLock || level == kAbortLock);
  }
}

inline void BaseMutex::RegisterAsUnlocked(Thread* self) {
  if (UNLIKELY(self == NULL)) {
    CheckUnattachedThread(level_);
    return;
  }
  if (level_ != kMonitorLock) {
    if (kDebugLocking && !gAborting) {
      CHECK(self->GetHeldMutex(level_) == this) << "Unlocking on unacquired mutex: " << name_;
    }
    self->SetHeldMutex(level_, NULL);
  }
}

inline void ReaderWriterMutex::SharedLock(Thread* self) {
  DCHECK(self == NULL || self == Thread::Current());
#if ART_USE_FUTEXES
  bool done = false;
  do {
    int32_t cur_state = state_;
    if (cur_state >= 0) {
      // Add as an extra reader.
      done = android_atomic_acquire_cas(cur_state, cur_state + 1, &state_) == 0;
    } else {
      // Owner holds it exclusively, hang up.
      ScopedContentionRecorder scr(this, GetExclusiveOwnerTid(), SafeGetTid(self));
      android_atomic_inc(&num_pending_readers_);
      if (futex(&state_, FUTEX_WAIT, cur_state, NULL, NULL, 0) != 0) {
        if (errno != EAGAIN) {
          PLOG(FATAL) << "futex wait failed for " << name_;
        }
      }
      android_atomic_dec(&num_pending_readers_);
    }
  } while(!done);
#else
  CHECK_MUTEX_CALL(pthread_rwlock_rdlock, (&rwlock_));
#endif
  RegisterAsLocked(self);
  AssertSharedHeld(self);
}

inline void ReaderWriterMutex::SharedUnlock(Thread* self) {
  DCHECK(self == NULL || self == Thread::Current());
  AssertSharedHeld(self);
  RegisterAsUnlocked(self);
#if ART_USE_FUTEXES
  bool done = false;
  do {
    int32_t cur_state = state_;
    if (LIKELY(cur_state > 0)) {
      // Reduce state by 1.
      done = android_atomic_release_cas(cur_state, cur_state - 1, &state_) == 0;
      if (done && (cur_state - 1) == 0) { // cas may fail due to noise?
        if (num_pending_writers_ > 0 || num_pending_readers_ > 0) {
          // Wake any exclusive waiters as there are now no readers.
          futex(&state_, FUTEX_WAKE, -1, NULL, NULL, 0);
        }
      }
    } else {
      LOG(FATAL) << "Unexpected state_:" << cur_state << " for " << name_;
    }
  } while(!done);
#else
  CHECK_MUTEX_CALL(pthread_rwlock_unlock, (&rwlock_));
#endif
}

}  // namespace art

#endif  // ART_SRC_BASE_MUTEX_INL_H_