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Re: odd socketpair() failure


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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