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