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Date:	Thu, 04 Aug 2011 08:00:34 +0200
From:	Marco atzeri <marco DOT atzeri AT gmail DOT com>
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To:	cygwin AT cygwin DOT com
Subject:	Re: odd socketpair() failure
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On 8/4/2011 1:09 AM, Eric Blake wrote:
> A while ago, I tested pipe() for EMFILE failures [1]. Well, I repeated
> those tests for socketpair() [2], and cygwin is once again the odd man out.
>
> [1] http://cygwin.com/ml/cygwin/2011-06/msg00328.html
> [2] http://austingroupbugs.net/view.php?id=483
>
> $ cat foo.c
> #define _POSIX_C_SOURCE 200811L
> #define __EXTENSIONS__ 1
> #include <sys/types.h>
> #include <sys/time.h>
> #include <unistd.h>
> #include <string.h>
> #include <stdio.h>
> #include <errno.h>
> #include <fcntl.h>
> #include <sys/socket.h>
> int
> main (int argc, char **argv)
> {
> int last;
> int fd[2] = {-2,-3};
> int err;
> /* Get to an EMFILE condition. */
> while (1) {
> int fd = open("/dev/null", O_RDONLY);
> if (fd < 0) {
> printf ("after fd %d, open failed with errno %d %s\n",
> last, errno, strerror(errno));
> break;
> }
> last = fd;
> }
> /* Probe behavior */
> err = socketpair(AF_UNIX, SOCK_STREAM, 0, fd);
> if (err)
> printf ("try 1, socketpair returned %d errno %d %s, fds %d %d\n",
> err, errno, strerror(errno), fd[0], fd[1]);
> else
> printf ("try 1, socketpair succeeded, fds %d %d\n", fd[0], fd[1]);
> if (close(last))
> return 1;
> err = socketpair(AF_UNIX, SOCK_STREAM, 0, fd);
> if (err)
> printf ("try 2, socketpair returned %d errno %d %s, fds %d %d\n",
> err, errno, strerror(errno), fd[0], fd[1]);
> else
> printf ("try 2, socketpair succeeded, fds %d %d\n", fd[0], fd[1]);
> if (close(0))
> return 1;
> err = socketpair(AF_UNIX, SOCK_STREAM, 0, fd);
> if (err)
> printf ("try 3, socketpair returned %d errno %d %s, fds %d %d\n",
> err, errno, strerror(errno), fd[0], fd[1]);
> else
> printf ("try 3, socketpair succeeded, fds %d %d\n", fd[0], fd[1]);
> return 0;
> }
> $ ./foo
> after fd 3199, open failed with errno 24 Too many open files
> try 1, socketpair returned -1 errno 24 Too many open files, fds -2 -3
> try 2, socketpair returned -1 errno 24 Too many open files, fds -2 -3
> try 3, socketpair returned -1 errno 24 Too many open files, fds -2 -3
>
> But on Linux, try 3 succeeds. Something in cygwin is not quite right on
> try 3 - the program explicitly freed two fd slots (0 and 3199), so it
> should have plenty of room to create the socketpair without hitting EMFILE.
>
> Disclaimer: I tested on 1.7.9 rather than the latest snapshot; maybe the
> pipe() fix in the meantime also fixed socketpair()?
>
same result on latest CVS

Marco

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