Re: pthread_kill: signals remain pending after target thread exits

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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John?  Ping?

On Oct 23 14:55, Corinna Vinschen wrote:
> On Oct 22 02:08, John Carey wrote:
> > > From: Corinna Vinschen [corinna-cygwin@cygwin.com]
> > > Sent: Wednesday, October 21, 2015 4:48 AM
> > > Subject: Re: pthread_kill: signals remain pending after target thread exits
> > ...
> > > > On Sep 11 18:11, John Carey wrote:
> > > > There seems to be a problem with pthread_kill: a pending signal
> > > > targeting a particular thread prevents other threads from receiving
> > > > signals sharing the same signal number--even after the original target
> > > > thread exits and is joined.
> > ...
> > > The important thing here is to get rid of the pending signal.
> > 
> > Yes, I agree that is the most important thing.
> > 
> > > > In my view it would be desirable if:
> > > >
> > > >   - Pending signals targeting a particular thread would not outlast
> > > >   that thread.
> > > 
> > > Since you looked into the code anyway, do you have an idea how to
> > > implement that?  For a start, do you have a simple testcase, only
> > > the bare code needed to reproduce the issue?
> > 
> > I've attached a test case that I *think* gets into the right spot, at
> > least for 64-bit Cygwin 2.0.4.  That is, it hangs trying to receive
> > the signal, instead of terminating.  (This test passes (terminates) in
> > 32-bit Cygwin 1.7.9 and 64-bit Ubuntu 14.04.3 LTS.)
> 
> Thanks for the testcase.  I applied a patch which hopefully works as
> desired, at least to fix the immediate problem of the remaining pending
> signal when a thread exits.  I uploaded a new developer snapshot to
> https://cygwin.com/snapshots.  Please give it a try.
> 
> Note that the today's snapshot does *NOT* contain the changes concerning
> the new ACL handling, so people testing that stuff should skip this
> snapshot.
> 
> > > >   - Multiple pending signals targeting different threads could
> > > >   coexist, even if they shared the same signal number.  This happens
> > > >   on Linux (Ubuntu 14.04.3), where I can generate two signals for two
> > > >   different threads, then sleep for a bit in each target thread, and
> > > >   finally have each thread receive its signal with sigwait()--neither
> > > >   signal is lost during the sleeping period.
> > > 
> > > That requires to extend the handling for pending signals.  That's
> > > a rather bigger task...
> > 
> > Yeah.  It's nice if threads don't interfere with each other, but this
> > part would indeed be harder to change.
> 
> I added that to my neverending TODO list.  Maybe I get around to it at
> one point.
> 
> 
> Thanks,
> Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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