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

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

#ifndef BASE_SYNCHRONIZATION_LOCK_H_

#define BASE_SYNCHRONIZATION_LOCK_H_

#include "base/base_export.h"

#include "base/logging.h"

#include "base/macros.h"

#include "base/synchronization/lock_impl.h"

#include "base/threading/platform_thread.h"

#include "build/build_config.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_EXPORT Lock {

 public:

#if !DCHECK_IS_ON()

   // 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: We do not permit recursive locks and 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  // DCHECK_IS_ON()

  // Whether Lock mitigates priority inversion when used from different thread

  // priorities.

  static bool HandlesMultipleThreadPriorities() {

#if defined(OS_POSIX)

    // POSIX mitigates priority inversion by setting the priority of a thread

    // holding a Lock to the maximum priority of any other thread waiting on it.

    return internal::LockImpl::PriorityInheritanceAvailable();

#elif defined(OS_WIN)

    // Windows mitigates priority inversion by randomly boosting the priority of

    // ready threads.

    // https://msdn.microsoft.com/library/windows/desktop/ms684831.aspx

    return true;

#else

#error Unsupported platform

#endif

  }

#if defined(OS_POSIX) || defined(OS_WIN)

  // Both Windows and POSIX implementations of ConditionVariable need to be

  // able to see our lock and tweak our debugging counters, as they release and

  // acquire locks inside of their condition variable APIs.

  friend class ConditionVariable;

#endif

 private:

#if DCHECK_IS_ON()

  // 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.

  base::PlatformThreadRef owning_thread_ref_;

#endif  // DCHECK_IS_ON()

  // 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:

  struct AlreadyAcquired {};

  explicit AutoLock(Lock& lock) : lock_(lock) {

    lock_.Acquire();

  }

  AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {

    lock_.AssertAcquired();

  }

  ~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  // BASE_SYNCHRONIZATION_LOCK_H_