[PATCH v2] Cygwin: pthread: Fix a race issue introduced by the commit 2c5433e5da82

[Bruno Haible]

Takashi Yano wrote in cygwin-patches:
> With v3 patch:
> int
> pthread::once (pthread_once_t *once_control, void (*init_routine) (void))
> {
>   /* Sign bit of once_control->state is used as done flag */
>   if (once_control->state & INT_MIN)
>     return 0;
> 
>   /* The type of &once_control->state is int *, which is compatible with
>      LONG * (the type of the first argument of InterlockedIncrement()). */
>   InterlockedIncrement (&once_control->state);
>   pthread_mutex_lock (&once_control->mutex);
>   if (!(once_control->state & INT_MIN))
>     {
>       init_routine ();
>       InterlockedOr (&once_control->state, INT_MIN);
>     }
>   pthread_mutex_unlock (&once_control->mutex);
>   if (InterlockedDecrement (&once_control->state) == INT_MIN)
>     pthread_mutex_destroy (&once_control->mutex);
>   return 0;
> }

Looks good to me.

If it passes 10 or 100 runs of my test program from
<https://cygwin.com/pipermail/cygwin/2024-May/255987.html>,
I would say, it's good.

Thanks!

Bruno