src/starboard/common/recursive_mutex.h

// Copyright 2018 The Cobalt Authors. All Rights Reserved.
//
// 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 STARBOARD_COMMON_RECURSIVE_MUTEX_H_
#define STARBOARD_COMMON_RECURSIVE_MUTEX_H_

#include "starboard/condition_variable.h"
#include "starboard/configuration.h"
#include "starboard/mutex.h"
#include "starboard/thread.h"
#include "starboard/time.h"

namespace starboard {

// A cross platform RecursiveMutex implementation. It is intended to replace
// std::recursive_mutex.
class RecursiveMutex {
 public:
  RecursiveMutex();
  ~RecursiveMutex();

  // The caller is blocked only if the mutex is being held by another thread.
  // If the caller already have the RecursiveMutex, Release() will succeed.
  // Otherwise Acquire() will block the caller until mutex is released.
  void Acquire();

  // The caller releases the mutex only when it calls Release() as many times
  // as Release().
  void Release();

  // Non-blocking function.
  // Acquires the RecursiveMutex if the mutex is free and returns true.
  // Only returns false if mutex is being held by another thread.
  bool AcquireTry();

 private:
  Mutex mutex_;
  SbThreadId owner_id_;
  // Only the owner is able to modify recurse_count_.
  size_t recurse_count_;

  SB_DISALLOW_COPY_AND_ASSIGN(RecursiveMutex);
};

////////////////////////// Implementation /////////////////////////////////////

inline RecursiveMutex::RecursiveMutex()
    : owner_id_(kSbThreadInvalidId), recurse_count_(0) {}

inline RecursiveMutex::~RecursiveMutex() {}

inline void RecursiveMutex::Acquire() {
  SbThreadId current_thread = SbThreadGetId();
  if (owner_id_ == current_thread) {
    recurse_count_++;
    SB_DCHECK(recurse_count_ > 0);
    return;
  }
  mutex_.Acquire();
  owner_id_ = current_thread;
  recurse_count_ = 1;
}

inline void RecursiveMutex::Release() {
  SB_DCHECK(owner_id_ == SbThreadGetId());
  if (owner_id_ == SbThreadGetId()) {
    SB_DCHECK(0 < recurse_count_);
    recurse_count_--;
    if (recurse_count_ == 0) {
      owner_id_ = kSbThreadInvalidId;
      mutex_.Release();
    }
  }
}

inline bool RecursiveMutex::AcquireTry() {
  SbThreadId current_thread = SbThreadGetId();
  if (owner_id_ == current_thread) {
    recurse_count_++;
    SB_DCHECK(recurse_count_ > 0);
    return true;
  }
  if (!mutex_.AcquireTry()) {
    return false;
  }
  owner_id_ = current_thread;
  recurse_count_ = 1;
  return true;
}

class ScopedRecursiveLock {
 public:
  explicit ScopedRecursiveLock(RecursiveMutex& mutex) : mutex_(mutex) {
    mutex_.Acquire();
  }

  ~ScopedRecursiveLock() { mutex_.Release(); }

 private:
  RecursiveMutex& mutex_;
  SB_DISALLOW_COPY_AND_ASSIGN(ScopedRecursiveLock);
};

}  // namespace starboard.

#endif  // STARBOARD_COMMON_RECURSIVE_MUTEX_H_