From: Ken Brown <kbrown@cornell.edu>
To: cygwin@cygwin.com
Subject: Re: Another pipe-related problem?
Date: Tue, 9 Nov 2021 17:16:31 -0500 [thread overview]
Message-ID: <0971ace1-5ee8-bdcc-5fd9-4551b294ebf8@cornell.edu> (raw)
In-Reply-To: <eb8d7d4f-d1ed-6f30-2ac3-1b24166243d9@cornell.edu>
On 11/9/2021 9:11 AM, Ken Brown via Cygwin wrote:
> On 11/9/2021 5:55 AM, Henry S. Thompson wrote:
>> As you may know, the XEmacs situation is complicated. The old source
>> repo (bitbucket.org/xemacs) no longer exists. There's a fork that's
>> still being maintained, but it's not widely publicised. That's the
>> one I'm working with -- are you aware of this.
>
> I was aware that the bitbucket repo didn't exist, because I tried to get the
> sources there. But I didn't know about the fork. Please point me to it, or
> just make a tarball available to me somehow.
>
>> Here are the immediate contexts from the sources for the xemacs
>> sources in the above backtrace, might be enough to check your
>> hypothesis:
>>
>> sysdep.c:
>>
>> retry_read_1 (int fildes, void *buf, size_t nbyte, int allow_quit)
>> {
>> ssize_t rtnval;
>>
>> while ((rtnval = read (fildes, buf, nbyte)) == -1
>> && (errno == EINTR)) <<<<<<<<<<<<<<<<<<<<
>> {
>> if (allow_quit)
>> QUIT;
>> }
>> return rtnval;
>> }
> 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 was able to build XEmacs and reproduce the problem. My guess was wrong,
though my question to Takashi still stands. I think the infinite loop is
actually caused by a bug in fhandler_pipe::raw_read that only affects
non-blocking pipes (which is what we have in XEmacs).
Consider the following code in fhandler_pipe::raw_read:
status = NtReadFile (get_handle (), evt, NULL, NULL, &io, ptr,
len1, NULL, NULL);
if (evt && status == STATUS_PENDING) <<<<<<<<<<<<<<<<<<<<<<<<<<<<
{
waitret = cygwait (evt, INFINITE, cw_cancel | cw_sig);
[...]
}
In the non-blocking case, evt == NULL, but we still might have status ==
STATUS_PENDING. We then should wait on get_handle() to let NtReadFile finish.
By not waiting, we end up using a garbage value from io.Information, leading to
an infinite loop in drain_signal_event_pipe.
I'll try to fix this.
Ken
next prev parent reply other threads:[~2021-11-09 22:16 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-08 13:12 Henry S. Thompson
2021-11-08 14:35 ` Ken Brown
2021-11-08 18:52 ` Ken Brown
2021-11-09 10:55 ` Henry S. Thompson
2021-11-09 14:11 ` Ken Brown
2021-11-09 14:47 ` Henry S. Thompson
2021-11-09 22:16 ` Ken Brown [this message]
2021-11-09 22:20 ` Ken Brown
2021-11-10 2:53 ` Ken Brown
2021-11-10 3:51 ` Backwoods BC
2021-11-10 14:47 ` Ken Brown
2021-11-10 17:23 ` Henry S. Thompson
2021-11-10 18:03 ` Ken Brown
2021-11-10 18:42 ` Henry S. Thompson
2021-11-10 23:07 ` Andrey Repin
2021-11-11 11:06 ` Andrey Repin
2021-11-11 14:16 ` Ken Brown
2021-12-08 21:09 ` XEmacs versus Cygwin 3.3 (was Re: Another pipe-related problem?) Henry S. Thompson
2021-12-09 8:39 ` Aidan Kehoe
2021-11-09 23:22 ` Another pipe-related problem? Takashi Yano
2021-11-09 23:29 ` Takashi Yano
2021-11-09 23:48 ` Takashi Yano
2021-11-10 0:16 ` Takashi Yano
2021-11-10 0:37 ` Takashi Yano
2021-11-10 2:02 ` Ken Brown
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