From: Philippe Troin <phil@fifi.org>
To: Eli Barzilay <eli@barzilay.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Repost: Bug with select?
Date: 25 Jul 2003 17:35:17 -0700 [thread overview]
Message-ID: <877k66qg56.fsf@ceramic.fifi.org> (raw)
In-Reply-To: <16159.28266.868297.372200@mojave.cs.cornell.edu>
Eli Barzilay <eli@barzilay.org> writes:
> [This is a second post, since I didn't get any replies the first time.
> It looks more like a bug now, which sounds strange for something that
> common...]
>
> When I run the following program, and block the terminal's output
> (C-s), the `select' doesn't seem to have any effect, resulting in a
> 100% cpu usage (this is on a RH8, with 2.4.18). I wouldn't be
> surprised if I'm doing something stupid, but it does seem to work fine
> on Solaris.
>
> Is there anything wrong with this, or is this some bug?
>
> ======================================================================
> #include <unistd.h>
> #include <fcntl.h>
> int main() {
> int flags, fd, len; fd_set writefds;
> fd = 1;
> flags = fcntl(fd, F_GETFL, 0);
> fcntl(fd, F_SETFL, flags | O_NONBLOCK);
> while (1) {
> FD_ZERO(&writefds);
> FD_SET(fd, &writefds);
> len = select(fd + 1, NULL, &writefds, NULL, NULL);
> if (!FD_ISSET(fd,&writefds)) exit(0);
> len = write(fd, "hi\n", 3);
> }
> fcntl(fd, F_SETFL, flags);
> }
> ======================================================================
Looks like a bug to me.
Strace says:
select(2, NULL, [1], NULL, NULL) = 1 (out [1])
write(1, "hi\n", 3) = -1 EAGAIN (Resource temporarily unavailable)
forever.
Then select() should not return fd 1 as writable, at least not
reapeatedly.
Phil.
next prev parent reply other threads:[~2003-07-26 0:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-06-18 8:49 Problem with select? Eli Barzilay
2003-07-24 5:28 ` Repost: Bug " Eli Barzilay
2003-07-25 13:41 ` Marco Roeland
2003-07-26 0:20 ` Ben Greear
2003-07-26 9:05 ` Marco Roeland
2003-07-26 0:35 ` Philippe Troin [this message]
2003-07-26 14:29 ` Eli Barzilay
2003-07-26 14:25 ` Eli Barzilay
2003-07-26 15:37 ` Marco Roeland
2003-07-27 19:29 Manfred Spraul
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