Re: Possiblly bug of cygwin1.dll

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Mon, 22 Jan 2024 10:25:28 +0100
Corinna Vinschen wrote:
> On Jan 22 12:30, Takashi Yano via Cygwin wrote:
> > PATCH2: (for cygwin)
> > Avoid handle leak caused when non-static pthread_once_t is initialized
> > with PTHREAD_ONCE_INIT
> > diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
> > index 7bb4f9fc8..127569160 100644
> > --- a/winsup/cygwin/thread.cc
> > +++ b/winsup/cygwin/thread.cc
> > @@ -2060,6 +2060,9 @@ pthread::once (pthread_once_t *once_control, void (*init_routine) (void))
> >      {
> >        init_routine ();
> >        once_control->state = 1;
> > +      pthread_mutex_unlock (&once_control->mutex);
> > +      while (pthread_mutex_destroy (&once_control->mutex) == EBUSY);
> > +      return 0;
> >      }
> >    /* Here we must remove our cancellation handler */
> >    pthread_mutex_unlock (&once_control->mutex);
> 
> I see what you're doing here.  Wouldn't it be simpler, though, to do this?
> 
> diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
> index 7bb4f9fc8341..7ec3aace395d 100644
> --- a/winsup/cygwin/thread.cc
> +++ b/winsup/cygwin/thread.cc
> @@ -2063,6 +2063,7 @@ pthread::once (pthread_once_t *once_control, void (*init_routine) (void))
>      }
>    /* Here we must remove our cancellation handler */
>    pthread_mutex_unlock (&once_control->mutex);
> +  while (pthread_mutex_destroy (&once_control->mutex) == EBUSY);
>    return 0;
>  }

In this code, if several threads call pthread_once() at the same time,
only one thread will succeed pthread_mutex_destroy() and the others
will fail with EINVAL. But it does not matter. The code will be
simpler.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>