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1/* getdtablesize() function for platforms that don't have it.
2 Copyright (C) 2008-2010 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2008.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
17
18#include <config.h>
19
20/* Specification. */
21#include <unistd.h>
22
23#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
24
25#include <stdio.h>
26
27/* Cache for the previous getdtablesize () result. */
28static int dtablesize;
29
30int
31getdtablesize (void)
32{
33 if (dtablesize == 0)
34 {
35 /* We are looking for the number N such that the valid file descriptors
36 are 0..N-1. It can be obtained through a loop as follows:
37 {
38 int fd;
39 for (fd = 3; fd < 65536; fd++)
40 if (dup2 (0, fd) == -1)
41 break;
42 return fd;
43 }
44 On Windows XP, the result is 2048.
45 The drawback of this loop is that it allocates memory for a libc
46 internal array that is never freed.
47
48 The number N can also be obtained as the upper bound for
49 _getmaxstdio (). _getmaxstdio () returns the maximum number of open
50 FILE objects. The sanity check in _setmaxstdio reveals the maximum
51 number of file descriptors. This too allocates memory, but it is
52 freed when we call _setmaxstdio with the original value. */
53 int orig_max_stdio = _getmaxstdio ();
54 unsigned int bound;
55 for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
56 ;
57 _setmaxstdio (orig_max_stdio);
58 dtablesize = bound;
59 }
60 return dtablesize;
61}
62
63#endif