src/pagespeed/kernel/base/abstract_mutex.h

/*
 * Copyright 2010 Google Inc.
 *
 * 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.
 */

// Author: jmarantz@google.com (Joshua Marantz)

#ifndef PAGESPEED_KERNEL_BASE_ABSTRACT_MUTEX_H_
#define PAGESPEED_KERNEL_BASE_ABSTRACT_MUTEX_H_

#include "pagespeed/kernel/base/basictypes.h"
#include "pagespeed/kernel/base/thread_annotations.h"

namespace net_instaweb {

// Abstract interface for implementing a mutex.
class LOCKABLE AbstractMutex {
 public:
  virtual ~AbstractMutex();
  // Attempt to take mutex, true on success, false if held by another thread.
  virtual bool TryLock() EXCLUSIVE_TRYLOCK_FUNCTION(true) = 0;
  // Block until mutex is available, then take the mutex.
  virtual void Lock() EXCLUSIVE_LOCK_FUNCTION() = 0;
  // Release the mutex, permitting a blocked lock operation (if any) to proceed.
  virtual void Unlock() UNLOCK_FUNCTION() = 0;
  // Optionally checks that lock is held (for invariant checking purposes).
  // Default implementation does no checking.
  virtual void DCheckLocked();
  // Optionally checks that lock is not held (for invariant checking purposes).
  // Default implementation does no checking.
  virtual void DCheckUnlocked();
};

// Helper class for lexically scoped mutexing.
class SCOPED_LOCKABLE ScopedMutex {
 public:
  explicit ScopedMutex(AbstractMutex* mutex) EXCLUSIVE_LOCK_FUNCTION(mutex)
      : mutex_(mutex) {
    mutex_->Lock();
  }

  void Release() UNLOCK_FUNCTION() {
    if (mutex_ != NULL) {
      mutex_->Unlock();
      mutex_ = NULL;
    }
  }

  ~ScopedMutex() UNLOCK_FUNCTION() { Release(); }

 private:
  AbstractMutex* mutex_;

  DISALLOW_COPY_AND_ASSIGN(ScopedMutex);
};
// Catch bug where variable name is omitted with ScopedMutex, e.g.
// ScopedMutex(&mu);
#define ScopedMutex(x) COMPILE_ASSERT(0, mutex_lock_decl_missing_var_name)

}  // namespace net_instaweb

#endif  // PAGESPEED_KERNEL_BASE_ABSTRACT_MUTEX_H_