/* -*- 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_StaticMutex_h #define mozilla_StaticMutex_h #include "mozilla/Atomics.h" #include "mozilla/Mutex.h" namespace mozilla { /** * StaticMutex is a Mutex that can (and in fact, must) be used as a * global/static variable. * * The main reason to use StaticMutex as opposed to * StaticAutoPtr<OffTheBooksMutex> is that we instantiate the StaticMutex in a * thread-safe manner the first time it's used. * * The same caveats that apply to StaticAutoPtr apply to StaticMutex. In * particular, do not use StaticMutex as a stack variable or a class instance * variable, because this class relies on the fact that global variablies are * initialized to 0 in order to initialize mMutex. It is only safe to use * StaticMutex as a global or static variable. */ class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS StaticMutex { public: // In debug builds, check that mMutex is initialized for us as we expect by // the compiler. In non-debug builds, don't declare a constructor so that // the compiler can see that the constructor is trivial. #ifdef DEBUG StaticMutex() { MOZ_ASSERT(!mMutex); } #endif void Lock() { Mutex()->Lock(); } void Unlock() { Mutex()->Unlock(); } void AssertCurrentThreadOwns() { #ifdef DEBUG Mutex()->AssertCurrentThreadOwns(); #endif } private: OffTheBooksMutex* Mutex() { if (mMutex) { return mMutex; } OffTheBooksMutex* mutex = new OffTheBooksMutex("StaticMutex"); if (!mMutex.compareExchange(nullptr, mutex)) { delete mutex; } return mMutex; } Atomic<OffTheBooksMutex*> mMutex; // Disallow copy constructor, but only in debug mode. We only define // a default constructor in debug mode (see above); if we declared // this constructor always, the compiler wouldn't generate a trivial // default constructor for us in non-debug mode. #ifdef DEBUG StaticMutex(StaticMutex& aOther); #endif // Disallow these operators. StaticMutex& operator=(StaticMutex* aRhs); static void* operator new(size_t) CPP_THROW_NEW; static void operator delete(void*); }; typedef BaseAutoLock<StaticMutex> StaticMutexAutoLock; typedef BaseAutoUnlock<StaticMutex> StaticMutexAutoUnlock; } // namespace mozilla #endif