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Date:	Mon, 22 Jan 2024 12:49:55 +0100
To:	cygwin AT cygwin DOT com
Subject:	Re: Possiblly bug of cygwin1.dll
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From:	Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Cc:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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On Jan 22 20:16, Takashi Yano via Cygwin wrote:
> On Mon, 22 Jan 2024 10:57:48 +0100
> Corinna Vinschen wrote:
> > On Jan 22 10:25, Corinna Vinschen via Cygwin 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 */
> > 
> > Strange enough, this comment accompanies the code since its inception
> > in 2001.  It says explicitly "remove" the cancellation handler.
> > That sounds like the idea was right, just the programmer forgot about
> > it afterwards...
> 
> I am not sure what 'cancellation handler' means here. Is it the
> event handler in pthread_mutex_t?

Aaah, no.  I just read and re-read the stuff and it occured to me that
this is based on the preceeding, longer comment in pthread::once.
Theoretically, the comments say, we need to set up a cancellation handler
so pthread_once becomes cancellable.

However, I don't find this in the standards.  pthread_once is neither
one of the required cancellation points, nor one of the optional
cancellation points.

So now I wonder if we shouldn't just get rid of the cokmments talking
about the cancellation in pthread::once entirely.


Corinna

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