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Re: [c++-pthreads] Initialization of local static mutex

  • To: Roland Schwarz <roland.schwarz@xxxxxxxxx>
  • Subject: Re: [c++-pthreads] Initialization of local static mutex
  • From: Mark Mitchell <mark@xxxxxxxxxxxxxxxx>
  • Date: Sun, 08 Oct 2006 09:25:16 -0700
Roland Schwarz wrote:

I am unsure if it is thread safe to use a local
static mutex in the following manner:

void foo()
{
    static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_loc(&mutex);

    ...

    pthread_mutex_unlock(&mutex);
}

I am unsure because the standard says:

6.7/4:
"The zero-initialization of all local objects with static
storage duration is performed before any other initialization
takes place. A local object of POD type with static storage
duration initialized with constant-expressions is initialized
before its block is first entered. ..."
PTHREAD_MUTEX_INITIALIZER is supposed to be a constant-expression (like "-1" or "{ 1, 0 }"), so the initialization will happen before foo is called, typically at program start-up. 


I am hoping that I misunderstand the standard here, and that
the above is indeed thread-safe.
I believe your code is thread-safe in practice for the particular case of PTHREAD_MUTEX_INITIALIZER. 

--
Mark Mitchell
CodeSourcery
mark@xxxxxxxxxxxxxxxx
(650) 331-3385 x713