Re: Singleton_pattern and Thread Safety

"Chris M. Thomasson" <>
Sat, 11 Dec 2010 18:01:52 -0800
"Chris M. Thomasson" <> wrote in message

"Leigh Johnston" <> wrote in message

template<typename T>
T& meyers_singleton()
       static T* g_global = NULL;
       T* local = ATOMIC_LOAD_DEPENDS(&g_global);

       if (! local)
           static pthread_mutex_t g_mutex = PTHREAD_MUTEX_INITIALIZER;
           thread* const self_thread = pthread_get_specific(...);

00: static T g_instance;

           // simulated memory release barrier
01: pthread_mutex_lock(&self_thread->m_acquire);
02: pthread_mutex_unlock(&self_thread->m_release);
03: pthread_mutex_lock(&self_thread->m_release);
04: pthread_mutex_unlock(&self_thread->m_acquire);

here is a simplification:

           // simulated memory release barrier

No code below the lock can rise above it, and no code above the unlock can
sink below it.

This will produce proper release barrier on many existing POSIX
implementations for a plurality of architectures. I cannot think of a
PThread mutex implementation that gets around all explicit membars in the
internal `pthread_mutex_lock/unlock' code.

I do know of some Java proposals...

           // atomically produce the object
05: ATOMIC_STORE_NAKED(&g_global, &g_instance);
06: local = &g_instance;


   return local;

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