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Date: Wed, 10 Nov 2021 09:37:41 +0900
To: cygwin@cygwin.com
Subject: Re: Another pipe-related problem?
Message-Id: <20211110093741.d15b99a1361e680f87b61fd8@nifty.ne.jp>
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From: Takashi Yano via Cygwin <cygwin@cygwin.com>
Reply-To: Takashi Yano <takashi.yano@nifty.ne.jp>
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On Wed, 10 Nov 2021 09:16:13 +0900
Takashi Yano wrote:
> 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...
[...]
> 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.

Ah, however, should we handle WAIT_CANCELED here and call
pthread::static_cancel_self() as following?

   DWORD waitret = cygwait (read_mtx, timeout);
   switch (waitret)
     {
     case WAIT_OBJECT_0:
       break;
     case WAIT_TIMEOUT:
       set_errno (EAGAIN);
       len = (size_t) -1;
       return;
     WAIT_SIGNALED:
       set_errno (EINTR);
       len = (size_t) -1;
       return;
     WAIT_CANCELED:
       pthread::static_cancel_self ();
       /* NOTREACHED */
     default:
       /* Should not reach here. */
       __seterrno ();
       len = (slze_t) -1;
       return;
     }


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

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