client/base/synchronization/lock.h

/*
  Copyright 2014 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.
*/

#ifndef GOOPY_BASE_SYNCHRONIZATION_LOCK_H_
#define GOOPY_BASE_SYNCHRONIZATION_LOCK_H_
#pragma once

#include "base/base_api.h"
#include "base/synchronization/lock_impl.h"
#include "base/threading/platform_thread.h"

namespace base {

// A convenient wrapper for an OS specific critical section.  The only real
// intelligence in this class is in debug mode for the support for the
// AssertAcquired() method.
class BASE_API Lock {
 public:
#if defined(NDEBUG)             // Optimized wrapper implementation
  Lock() : lock_() {}
  ~Lock() {}
  void Acquire() { lock_.Lock(); }
  void Release() { lock_.Unlock(); }

  // If the lock is not held, take it and return true. If the lock is already
  // held by another thread, immediately return false. This must not be called
  // by a thread already holding the lock (what happens is undefined and an
  // assertion may fail).
  bool Try() { return lock_.Try(); }

  // Null implementation if not debug.
  void AssertAcquired() const {}
#else
  Lock();
  ~Lock() {}

  // NOTE: Although windows critical sections support recursive locks, we do not
  // allow this, and we will commonly fire a DCHECK() if a thread attempts to
  // acquire the lock a second time (while already holding it).
  void Acquire() {
    lock_.Lock();
    CheckUnheldAndMark();
  }
  void Release() {
    CheckHeldAndUnmark();
    lock_.Unlock();
  }

  bool Try() {
    bool rv = lock_.Try();
    if (rv) {
      CheckUnheldAndMark();
    }
    return rv;
  }

  void AssertAcquired() const;
#endif                          // NDEBUG

#if defined(OS_POSIX)
  // The posix implementation of ConditionVariable needs to be able
  // to see our lock and tweak our debugging counters, as it releases
  // and acquires locks inside of pthread_cond_{timed,}wait.
  // Windows doesn't need to do this as it calls the Lock::* methods.
  friend class ConditionVariable;
#endif

 private:
#if !defined(NDEBUG)
  // Members and routines taking care of locks assertions.
  // Note that this checks for recursive locks and allows them
  // if the variable is set.  This is allowed by the underlying implementation
  // on windows but not on Posix, so we're doing unneeded checks on Posix.
  // It's worth it to share the code.
  void CheckHeldAndUnmark();
  void CheckUnheldAndMark();

  // All private data is implicitly protected by lock_.
  // Be VERY careful to only access members under that lock.

  // Determines validity of owning_thread_id_.  Needed as we don't have
  // a null owning_thread_id_ value.
  bool owned_by_thread_;
  base::PlatformThreadId owning_thread_id_;
#endif  // NDEBUG

  // Platform specific underlying lock implementation.
  internal::LockImpl lock_;

  DISALLOW_COPY_AND_ASSIGN(Lock);
};

// A helper class that acquires the given Lock while the AutoLock is in scope.
class AutoLock {
 public:
  explicit AutoLock(Lock& lock) : lock_(lock) {
    lock_.Acquire();
  }

  ~AutoLock() {
    lock_.AssertAcquired();
    lock_.Release();
  }

 private:
  Lock& lock_;
  DISALLOW_COPY_AND_ASSIGN(AutoLock);
};

// AutoUnlock is a helper that will Release() the |lock| argument in the
// constructor, and re-Acquire() it in the destructor.
class AutoUnlock {
 public:
  explicit AutoUnlock(Lock& lock) : lock_(lock) {
    // We require our caller to have the lock.
    lock_.AssertAcquired();
    lock_.Release();
  }

  ~AutoUnlock() {
    lock_.Acquire();
  }

 private:
  Lock& lock_;
  DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
};

}  // namespace base

#endif  // GOOPY_BASE_SYNCHRONIZATION_LOCK_H_// Copyright (c) 2011 The Chromium Authors. All rights reserved.