pthread_mutex_t initializer idiom

[Peter Dimov]

Benjamin Kosnik wrote:
> I'm still trying to unify some of the atomics and concurrency code,
> and remove duplicates.
>
> I see this idiom a lot:
>
>   __gthread_mutex_t temp = __GTHREAD_MUTEX_INIT;
>   _M_mutex = temp;
>
> Can somebody explain to me why we are doing this instead of:
>
> _M_mutex = __GTHREAD_MUTEX_INIT;
>
> ?

It is presumably to cover the case where __GTHREAD_MUTEX_INIT expands to 
something like { 0, 0 }.