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/* getdtablesize() function for platforms that don't have it.
Copyright (C) 2008-2010 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2008.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include <unistd.h>
#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
#include <stdio.h>
/* Cache for the previous getdtablesize () result. */
static int dtablesize;
int
getdtablesize (void)
{
if (dtablesize == 0)
{
/* We are looking for the number N such that the valid file descriptors
are 0..N-1. It can be obtained through a loop as follows:
{
int fd;
for (fd = 3; fd < 65536; fd++)
if (dup2 (0, fd) == -1)
break;
return fd;
}
On Windows XP, the result is 2048.
The drawback of this loop is that it allocates memory for a libc
internal array that is never freed.
The number N can also be obtained as the upper bound for
_getmaxstdio (). _getmaxstdio () returns the maximum number of open
FILE objects. The sanity check in _setmaxstdio reveals the maximum
number of file descriptors. This too allocates memory, but it is
freed when we call _setmaxstdio with the original value. */
int orig_max_stdio = _getmaxstdio ();
unsigned int bound;
for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
;
_setmaxstdio (orig_max_stdio);
dtablesize = bound;
}
return dtablesize;
}
#endif
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