1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/xpcom/base/StaticMutex.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,90 @@
1.4 +#ifndef mozilla_StaticMutex_h
1.5 +#define mozilla_StaticMutex_h
1.6 +
1.7 +#include "mozilla/Atomics.h"
1.8 +#include "mozilla/Mutex.h"
1.9 +
1.10 +namespace mozilla {
1.11 +
1.12 +/**
1.13 + * StaticMutex is a Mutex that can (and in fact, must) be used as a
1.14 + * global/static variable.
1.15 + *
1.16 + * The main reason to use StaticMutex as opposed to
1.17 + * StaticAutoPtr<OffTheBooksMutex> is that we instantiate the StaticMutex in a
1.18 + * thread-safe manner the first time it's used.
1.19 + *
1.20 + * The same caveats that apply to StaticAutoPtr apply to StaticMutex. In
1.21 + * particular, do not use StaticMutex as a stack variable or a class instance
1.22 + * variable, because this class relies on the fact that global variablies are
1.23 + * initialized to 0 in order to initialize mMutex. It is only safe to use
1.24 + * StaticMutex as a global or static variable.
1.25 + */
1.26 +class StaticMutex
1.27 +{
1.28 +public:
1.29 + // In debug builds, check that mMutex is initialized for us as we expect by
1.30 + // the compiler. In non-debug builds, don't declare a constructor so that
1.31 + // the compiler can see that the constructor is trivial.
1.32 +#ifdef DEBUG
1.33 + StaticMutex()
1.34 + {
1.35 + MOZ_ASSERT(!mMutex);
1.36 + }
1.37 +#endif
1.38 +
1.39 + void Lock()
1.40 + {
1.41 + Mutex()->Lock();
1.42 + }
1.43 +
1.44 + void Unlock()
1.45 + {
1.46 + Mutex()->Unlock();
1.47 + }
1.48 +
1.49 + void AssertCurrentThreadOwns()
1.50 + {
1.51 +#ifdef DEBUG
1.52 + Mutex()->AssertCurrentThreadOwns();
1.53 +#endif
1.54 + }
1.55 +
1.56 +private:
1.57 + OffTheBooksMutex* Mutex()
1.58 + {
1.59 + if (mMutex) {
1.60 + return mMutex;
1.61 + }
1.62 +
1.63 + OffTheBooksMutex* mutex = new OffTheBooksMutex("StaticMutex");
1.64 + if (!mMutex.compareExchange(nullptr, mutex)) {
1.65 + delete mutex;
1.66 + }
1.67 +
1.68 + return mMutex;
1.69 + }
1.70 +
1.71 + Atomic<OffTheBooksMutex*> mMutex;
1.72 +
1.73 +
1.74 + // Disallow copy constructor, but only in debug mode. We only define
1.75 + // a default constructor in debug mode (see above); if we declared
1.76 + // this constructor always, the compiler wouldn't generate a trivial
1.77 + // default constructor for us in non-debug mode.
1.78 +#ifdef DEBUG
1.79 + StaticMutex(StaticMutex &other);
1.80 +#endif
1.81 +
1.82 + // Disallow these operators.
1.83 + StaticMutex& operator=(StaticMutex* rhs);
1.84 + static void* operator new(size_t) CPP_THROW_NEW;
1.85 + static void operator delete(void*);
1.86 +};
1.87 +
1.88 +typedef BaseAutoLock<StaticMutex> StaticMutexAutoLock;
1.89 +typedef BaseAutoUnlock<StaticMutex> StaticMutexAutoUnlock;
1.90 +
1.91 +} // namespace mozilla
1.92 +
1.93 +#endif
