gecko-dev/xpcom/glue/Mutex.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_Mutex_h
#define mozilla_Mutex_h

#include "prlock.h"

#include "mozilla/BlockingResourceBase.h"
#include "mozilla/GuardObjects.h"

//
// Provides:
//
//  - Mutex, a non-recursive mutex
//  - MutexAutoLock, an RAII class for ensuring that Mutexes are properly
//    locked and unlocked
//  - MutexAutoUnlock, complementary sibling to MutexAutoLock
//
//  - OffTheBooksMutex, a non-recursive mutex that doesn't do leak checking
//  - OffTheBooksMutexAuto{Lock,Unlock} - Like MutexAuto{Lock,Unlock}, but for
//    an OffTheBooksMutex.
//
// Using MutexAutoLock/MutexAutoUnlock etc. is MUCH preferred to making bare
// calls to Lock and Unlock.
//
namespace mozilla {

/**
 * OffTheBooksMutex is identical to Mutex, except that OffTheBooksMutex doesn't
 * include leak checking.  Sometimes you want to intentionally "leak" a mutex
 * until shutdown; in these cases, OffTheBooksMutex is for you.
 */
class OffTheBooksMutex : BlockingResourceBase
{
public:
  /**
   * @param aName A name which can reference this lock
   * @returns If failure, nullptr
   *          If success, a valid Mutex* which must be destroyed
   *          by Mutex::DestroyMutex()
   **/
  explicit OffTheBooksMutex(const char* aName)
    : BlockingResourceBase(aName, eMutex)
  {
    mLock = PR_NewLock();
    if (!mLock) {
      NS_RUNTIMEABORT("Can't allocate mozilla::Mutex");
    }
  }

  ~OffTheBooksMutex()
  {
    NS_ASSERTION(mLock,
                 "improperly constructed Lock or double free");
    // NSPR does consistency checks for us
    PR_DestroyLock(mLock);
    mLock = 0;
  }

#ifndef DEBUG
  /**
   * Lock
   * @see prlock.h
   **/
  void Lock() { PR_Lock(mLock); }

  /**
   * Unlock
   * @see prlock.h
   **/
  void Unlock() { PR_Unlock(mLock); }

  /**
   * AssertCurrentThreadOwns
   * @see prlock.h
   **/
  void AssertCurrentThreadOwns() const {}

  /**
   * AssertNotCurrentThreadOwns
   * @see prlock.h
   **/
  void AssertNotCurrentThreadOwns() const {}

#else
  void Lock();
  void Unlock();

  void AssertCurrentThreadOwns() const
  {
    PR_ASSERT_CURRENT_THREAD_OWNS_LOCK(mLock);
  }

  void AssertNotCurrentThreadOwns() const
  {
    // FIXME bug 476536
  }

#endif  // ifndef DEBUG

private:
  OffTheBooksMutex();
  OffTheBooksMutex(const OffTheBooksMutex&);
  OffTheBooksMutex& operator=(const OffTheBooksMutex&);

  PRLock* mLock;

  friend class CondVar;
};

/**
 * Mutex
 * When possible, use MutexAutoLock/MutexAutoUnlock to lock/unlock this
 * mutex within a scope, instead of calling Lock/Unlock directly.
 */
class Mutex : public OffTheBooksMutex
{
public:
  explicit Mutex(const char* aName)
    : OffTheBooksMutex(aName)
  {
    MOZ_COUNT_CTOR(Mutex);
  }

  ~Mutex()
  {
    MOZ_COUNT_DTOR(Mutex);
  }

private:
  Mutex();
  Mutex(const Mutex&);
  Mutex& operator=(const Mutex&);
};

/**
 * MutexAutoLock
 * Acquires the Mutex when it enters scope, and releases it when it leaves
 * scope.
 *
 * MUCH PREFERRED to bare calls to Mutex.Lock and Unlock.
 */
template<typename T>
class MOZ_STACK_CLASS BaseAutoLock
{
public:
  /**
   * Constructor
   * The constructor aquires the given lock.  The destructor
   * releases the lock.
   *
   * @param aLock A valid mozilla::Mutex* returned by
   *              mozilla::Mutex::NewMutex.
   **/
  explicit BaseAutoLock(T& aLock MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
    : mLock(&aLock)
  {
    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    NS_ASSERTION(mLock, "null mutex");
    mLock->Lock();
  }

  ~BaseAutoLock(void)
  {
    mLock->Unlock();
  }

private:
  BaseAutoLock();
  BaseAutoLock(BaseAutoLock&);
  BaseAutoLock& operator=(BaseAutoLock&);
  static void* operator new(size_t) CPP_THROW_NEW;

  T* mLock;
  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

typedef BaseAutoLock<Mutex> MutexAutoLock;
typedef BaseAutoLock<OffTheBooksMutex> OffTheBooksMutexAutoLock;

/**
 * MutexAutoUnlock
 * Releases the Mutex when it enters scope, and re-acquires it when it leaves
 * scope.
 *
 * MUCH PREFERRED to bare calls to Mutex.Unlock and Lock.
 */
template<typename T>
class MOZ_STACK_CLASS BaseAutoUnlock
{
public:
  explicit BaseAutoUnlock(T& aLock MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
    : mLock(&aLock)
  {
    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    NS_ASSERTION(mLock, "null lock");
    mLock->Unlock();
  }

  ~BaseAutoUnlock()
  {
    mLock->Lock();
  }

private:
  BaseAutoUnlock();
  BaseAutoUnlock(BaseAutoUnlock&);
  BaseAutoUnlock& operator=(BaseAutoUnlock&);
  static void* operator new(size_t) CPP_THROW_NEW;

  T* mLock;
  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

typedef BaseAutoUnlock<Mutex> MutexAutoUnlock;
typedef BaseAutoUnlock<OffTheBooksMutex> OffTheBooksMutexAutoUnlock;

} // namespace mozilla


#endif // ifndef mozilla_Mutex_h