gecko-dev/xpcom/threads/Mutex.h

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/* -*- 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 "mozilla/BlockingResourceBase.h"
#include "mozilla/PlatformMutex.h"
#include "nsISupports.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 : public detail::MutexImpl, 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)
#ifdef DEBUG
,
mOwningThread(nullptr)
#endif
{
}
~OffTheBooksMutex() {
#ifdef DEBUG
MOZ_ASSERT(!mOwningThread, "destroying a still-owned lock!");
#endif
}
#ifndef DEBUG
/**
* Lock this mutex.
**/
void Lock() { this->lock(); }
/**
* Try to lock this mutex, returning true if we were successful.
**/
[[nodiscard]] bool TryLock() { return this->tryLock(); }
/**
* Unlock this mutex.
**/
void Unlock() { this->unlock(); }
/**
* Assert that the current thread owns this mutex in debug builds.
*
* Does nothing in non-debug builds.
**/
void AssertCurrentThreadOwns() const {}
/**
* Assert that the current thread does not own this mutex.
*
* Note that this function is not implemented for debug builds *and*
* non-debug builds due to difficulties in dealing with memory ordering.
*
* It is therefore mostly useful as documentation.
**/
void AssertNotCurrentThreadOwns() const {}
#else
void Lock();
[[nodiscard]] bool TryLock();
void Unlock();
void AssertCurrentThreadOwns() const;
void AssertNotCurrentThreadOwns() const {
// FIXME bug 476536
}
#endif // ifndef DEBUG
private:
OffTheBooksMutex();
OffTheBooksMutex(const OffTheBooksMutex&);
OffTheBooksMutex& operator=(const OffTheBooksMutex&);
friend class OffTheBooksCondVar;
#ifdef DEBUG
PRThread* mOwningThread;
#endif
};
/**
* 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);
}
MOZ_COUNTED_DTOR(Mutex)
private:
Mutex();
Mutex(const Mutex&);
Mutex& operator=(const Mutex&);
};
namespace detail {
template <typename T>
class MOZ_RAII BaseAutoUnlock;
/**
* 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_RAII 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) : mLock(aLock) { mLock.Lock(); }
~BaseAutoLock(void) { mLock.Unlock(); }
// Assert that aLock is the mutex passed to the constructor and that the
// current thread owns the mutex. In coding patterns such as:
//
// void LockedMethod(const BaseAutoLock<T>& aProofOfLock)
// {
// aProofOfLock.AssertOwns(mMutex);
// ...
// }
//
// Without this assertion, it could be that mMutex is not actually
// locked. It's possible to have code like:
//
// BaseAutoLock lock(someMutex);
// ...
// BaseAutoUnlock unlock(someMutex);
// ...
// LockedMethod(lock);
//
// and in such a case, simply asserting that the mutex pointers match is not
// sufficient; mutex ownership must be asserted as well.
//
// Note that if you are going to use the coding pattern presented above, you
// should use this method in preference to using AssertCurrentThreadOwns on
// the mutex you expected to be held, since this method provides stronger
// guarantees.
void AssertOwns(const T& aMutex) const {
MOZ_ASSERT(&aMutex == &mLock);
mLock.AssertCurrentThreadOwns();
}
private:
BaseAutoLock();
BaseAutoLock(BaseAutoLock&);
BaseAutoLock& operator=(BaseAutoLock&);
static void* operator new(size_t) noexcept(true);
friend class BaseAutoUnlock<T>;
T mLock;
};
template <typename MutexType>
BaseAutoLock(MutexType&) -> BaseAutoLock<MutexType&>;
} // namespace detail
typedef detail::BaseAutoLock<Mutex&> MutexAutoLock;
typedef detail::BaseAutoLock<OffTheBooksMutex&> OffTheBooksMutexAutoLock;
namespace detail {
/**
* BaseAutoUnlock
* 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_RAII BaseAutoUnlock {
public:
explicit BaseAutoUnlock(T aLock) : mLock(aLock) { mLock.Unlock(); }
explicit BaseAutoUnlock(BaseAutoLock<T>& aAutoLock) : mLock(aAutoLock.mLock) {
NS_ASSERTION(mLock, "null lock");
mLock->Unlock();
}
~BaseAutoUnlock() { mLock.Lock(); }
private:
BaseAutoUnlock();
BaseAutoUnlock(BaseAutoUnlock&);
BaseAutoUnlock& operator=(BaseAutoUnlock&);
static void* operator new(size_t) noexcept(true);
T mLock;
};
template <typename MutexType>
BaseAutoUnlock(MutexType&) -> BaseAutoUnlock<MutexType&>;
} // namespace detail
typedef detail::BaseAutoUnlock<Mutex&> MutexAutoUnlock;
typedef detail::BaseAutoUnlock<OffTheBooksMutex&> OffTheBooksMutexAutoUnlock;
} // namespace mozilla
#endif // ifndef mozilla_Mutex_h