Date: Mon, 22 Jan 2024 12:42:56 +0100
To: cygwin@cygwin.com
Subject: Re: Possiblly bug of cygwin1.dll
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From: Corinna Vinschen via Cygwin <cygwin@cygwin.com>
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Cc: Corinna Vinschen <corinna-cygwin@cygwin.com>
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On Jan 22 20:06, Takashi Yano via Cygwin wrote:
> 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.

Yeah, but you're right.  It's cleaner to do this only in the thread
actually performing the init action so your original patch makes
more sense.


Corinna

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