Another pipe-related problem?

Takashi Yano takashi.yano@nifty.ne.jp
Wed Nov 10 00:16:13 GMT 2021


On Wed, 10 Nov 2021 08:48:22 +0900
Takashi Yano wrote:
> On Wed, 10 Nov 2021 08:29:32 +0900
> Takashi Yano wrote:
> > On Wed, 10 Nov 2021 08:22:45 +0900
> > Takashi Yano wrote:
> > > On Tue, 9 Nov 2021 09:11:28 -0500
> > > Ken Brown wrote:
> > > > I'll have to reproduce the hang myself in order to test this (or maybe you could 
> > > > test it), but I now have a new guess: If the read call above keeps failing with 
> > > > EINTR, then we're in an infinite loop.  This could happen because of the 
> > > > following code in fhandler_pipe::raw_read:
> > > > 
> > > >    DWORD waitret = cygwait (read_mtx, timeout);
> > > >    switch (waitret)
> > > >      {
> > > >      case WAIT_OBJECT_0:
> > > >        break;
> > > >      case WAIT_TIMEOUT:
> > > >        set_errno (EAGAIN);
> > > >        len = (size_t) -1;
> > > >        return;
> > > >      default:
> > > >        set_errno (EINTR);
> > > >        len = (size_t) -1;
> > > >        return;
> > > >      }
> > > > 
> > > > Takashi, is EINTR really the appropriate errno in the default case?  Isn't 
> > > > cygwait supposed to handle signals?
> > > 
> > > I assume cygwait() returns WAIT_SIGNALED when signalled
> > > by SIGINT, SIGTERM, SIGTSTP, etc...  In this case, EINTR
> > > should return I think.
> > > 
> > > Is it wrong?
> > 
> > Ah, if SA_RESTART is set, we should continue to read even
> > if signalled...
> 
> So, should this be like following?
> 
>  restart_wait_read_mtx:
>    DWORD waitret = cygwait (read_mtx, timeout, cw_sig_eintr);
>    switch (waitret)
>      {
>      case WAIT_OBJECT_0:
>        break;
>      case WAIT_TIMEOUT:
>        set_errno (EAGAIN);
>        len = (size_t) -1;
>        return;
>      case WAIT_SIGNALED:
>        if (_my_tls.call_signal_handler ())
>          goto restart_wait_read_mtx;
>        set_errno (EINTR);
>        len = (size_t) -1;
>        return;
>      default:
>        /* Should not reach here. */
>        __seterrno ();
>        len = (size_t) -1;
>        return;
>      }

No, we don't have to do that because cygwait() do the same
internally. cygwain() returns WAIT_SIGNALED when signalled
only if SA_RESTART is not set. So, the current code LGTM.

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


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