Re: [PATCH] Cygwin: sigproc: Do not send signal to myself if exiting.

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

On Fri, 19 Nov 2021 16:53:57 +0100
Corinna Vinschen wrote:
> On Nov 19 16:51, Corinna Vinschen wrote:
> > Hi Takashi,
> > 
> > On Nov 19 20:50, Takashi Yano wrote:
> > > - This patch fixes the issue that process sometimes hangs for 60
> > >   seconds with the following scenario.
> > >     1) Open command prompt.
> > >     2) Run "c:\cygwin64\bin\bash -l"
> > >     3) Compipe the following source with mingw compiler.
> > >        /*--- Begin ---*/
> > >        #include <stdio.h>
> > >        int main() {return getchar();}
> > >        /*---- End ----*/
> > >     3) Run "tcsh -c ./a.exe"
> > >     4) Hit Ctrl-C.
> > > ---
> > >  winsup/cygwin/sigproc.cc | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
> > > index 97211edcf..9160dd160 100644
> > > --- a/winsup/cygwin/sigproc.cc
> > > +++ b/winsup/cygwin/sigproc.cc
> > > @@ -603,6 +603,10 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
> > >        its_me = false;
> > >      }
> > >  
> > > +  /* Do not send signal to myself if exiting. */
> > > +  if (its_me && exit_state > ES_EXIT_STARTING && si.si_signo > 0)
> > > +    goto out;
> > > +
> > >    if (its_me)
> > >      sendsig = my_sendsig;
> > >    else
> > > -- 
> > > 2.33.0
> > 
> > Isn't that already handled in wait_sig?  What's the difference here?
> 
> ...and where exactly is it waiting 60 secs?

If sending signal to myself with exit_state > ES_EXIT_STARGING,
wait_for_completion in sig_send() is set to true. Therefore,
sig_send() waits for pack.wakeup event for WSSC (60000 msec) here:

  /* No need to wait for signal completion unless this was a signal to
     this process.

     If it was a signal to this process, wait for a dispatched signal.
     Otherwise just wait for the wait_sig to signal that it has finished
     processing the signal.  */
  if (wait_for_completion)
    {
      sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup);
      rc = WaitForSingleObject (pack.wakeup, WSSC);
      ForceCloseHandle (pack.wakeup);
    }

However, thread wait_sig ignores the signal here:
      /* Don't process signals when we start exiting */
      if (exit_state > ES_EXIT_STARTING && pack.si.si_signo > 0)
        continue;
and does not call SetEvent (pack.wakeup).

As a result, sig_send() hangs for 60 secs.

With this patch, sig_send() does not send signal which will
be ignored in wait_sig().

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