webrtc/base/criticalsection.h

/*
 *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#ifndef WEBRTC_BASE_CRITICALSECTION_H__
#define WEBRTC_BASE_CRITICALSECTION_H__

#include "webrtc/base/constructormagic.h"
#include "webrtc/base/thread_annotations.h"

#if defined(WEBRTC_WIN)
// Include winsock2.h before including <windows.h> to maintain consistency with
// win32.h.  We can't include win32.h directly here since it pulls in
// headers such as basictypes.h which causes problems in Chromium where webrtc
// exists as two separate projects, webrtc and libjingle.
#include <winsock2.h>
#include <windows.h>
#include <sal.h>  // must come after windows headers.
#endif  // defined(WEBRTC_WIN)

#if defined(WEBRTC_POSIX)
#include <pthread.h>
#endif

#if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
#define CS_DEBUG_CHECKS 1
#endif

#if CS_DEBUG_CHECKS
#define CS_DEBUG_CODE(x) x
#else  // !CS_DEBUG_CHECKS
#define CS_DEBUG_CODE(x)
#endif  // !CS_DEBUG_CHECKS

namespace rtc {

class LOCKABLE CriticalSection {
 public:
  CriticalSection();
  ~CriticalSection();

  void Enter() EXCLUSIVE_LOCK_FUNCTION();
  bool TryEnter() EXCLUSIVE_TRYLOCK_FUNCTION(true);
  void Leave() UNLOCK_FUNCTION();

  // Use only for DCHECKing.
  bool CurrentThreadIsOwner() const;
  // Use only for DCHECKing.
  bool IsLocked() const;

 private:
#if defined(WEBRTC_WIN)
  CRITICAL_SECTION crit_;
#elif defined(WEBRTC_POSIX)
  pthread_mutex_t mutex_;
  CS_DEBUG_CODE(pthread_t thread_);
  CS_DEBUG_CODE(int recursion_count_);
#endif
};

// CritScope, for serializing execution through a scope.
class SCOPED_LOCKABLE CritScope {
 public:
  explicit CritScope(CriticalSection* cs) EXCLUSIVE_LOCK_FUNCTION(cs);
  ~CritScope() UNLOCK_FUNCTION();
 private:
  CriticalSection* const cs_;
  DISALLOW_COPY_AND_ASSIGN(CritScope);
};

// Tries to lock a critical section on construction via
// CriticalSection::TryEnter, and unlocks on destruction if the
// lock was taken. Never blocks.
//
// IMPORTANT: Unlike CritScope, the lock may not be owned by this thread in
// subsequent code. Users *must* check locked() to determine if the
// lock was taken. If you're not calling locked(), you're doing it wrong!
class TryCritScope {
 public:
  explicit TryCritScope(CriticalSection* cs);
  ~TryCritScope();
#if defined(WEBRTC_WIN)
  _Check_return_ bool locked() const;
#else
  bool locked() const __attribute__((warn_unused_result));
#endif
 private:
  CriticalSection* const cs_;
  const bool locked_;
  CS_DEBUG_CODE(mutable bool lock_was_called_);
  DISALLOW_COPY_AND_ASSIGN(TryCritScope);
};

// TODO: Move this to atomicops.h, which can't be done easily because of
// complex compile rules.
class AtomicOps {
 public:
#if defined(WEBRTC_WIN)
  // Assumes sizeof(int) == sizeof(LONG), which it is on Win32 and Win64.
  static int Increment(volatile int* i) {
    return ::InterlockedIncrement(reinterpret_cast<volatile LONG*>(i));
  }
  static int Decrement(volatile int* i) {
    return ::InterlockedDecrement(reinterpret_cast<volatile LONG*>(i));
  }
  static int Load(volatile const int* i) {
    return *i;
  }
  static void Store(volatile int* i, int value) {
    *i = value;
  }
  static int CompareAndSwap(volatile int* i, int old_value, int new_value) {
    return ::InterlockedCompareExchange(reinterpret_cast<volatile LONG*>(i),
                                        new_value,
                                        old_value);
  }
#else
  static int Increment(volatile int* i) {
    return __sync_add_and_fetch(i, 1);
  }
  static int Decrement(volatile int* i) {
    return __sync_sub_and_fetch(i, 1);
  }
  static int Load(volatile const int* i) {
    // Adding 0 is a no-op, so const_cast is fine.
    return __sync_add_and_fetch(const_cast<volatile int*>(i), 0);
  }
  static void Store(volatile int* i, int value) {
    __sync_synchronize();
    *i = value;
  }
  static int CompareAndSwap(volatile int* i, int old_value, int new_value) {
    return __sync_val_compare_and_swap(i, old_value, new_value);
  }
#endif
};


// A POD lock used to protect global variables. Do NOT use for other purposes.
// No custom constructor or private data member should be added.
class LOCKABLE GlobalLockPod {
 public:
  void Lock() EXCLUSIVE_LOCK_FUNCTION();

  void Unlock() UNLOCK_FUNCTION();

  volatile int lock_acquired;
};

class GlobalLock : public GlobalLockPod {
 public:
  GlobalLock();
};

} // namespace rtc

#endif // WEBRTC_BASE_CRITICALSECTION_H__