1/* getdtablesize() function for platforms that don't have it.
2   Copyright (C) 2008-2012 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#include "msvc-inval.h"
28
29#if HAVE_MSVC_INVALID_PARAMETER_HANDLER
30static int
31_setmaxstdio_nothrow (int newmax)
32{
33  int result;
34
35  TRY_MSVC_INVAL
36    {
37      result = _setmaxstdio (newmax);
38    }
39  CATCH_MSVC_INVAL
40    {
41      result = -1;
42    }
43  DONE_MSVC_INVAL;
44
45  return result;
46}
47# define _setmaxstdio _setmaxstdio_nothrow
48#endif
49
50/* Cache for the previous getdtablesize () result.  */
51static int dtablesize;
52
53int
54getdtablesize (void)
55{
56  if (dtablesize == 0)
57    {
58      /* We are looking for the number N such that the valid file descriptors
59         are 0..N-1.  It can be obtained through a loop as follows:
60           {
61             int fd;
62             for (fd = 3; fd < 65536; fd++)
63               if (dup2 (0, fd) == -1)
64                 break;
65             return fd;
66           }
67         On Windows XP, the result is 2048.
68         The drawback of this loop is that it allocates memory for a libc
69         internal array that is never freed.
70
71         The number N can also be obtained as the upper bound for
72         _getmaxstdio ().  _getmaxstdio () returns the maximum number of open
73         FILE objects.  The sanity check in _setmaxstdio reveals the maximum
74         number of file descriptors.  This too allocates memory, but it is
75         freed when we call _setmaxstdio with the original value.  */
76      int orig_max_stdio = _getmaxstdio ();
77      unsigned int bound;
78      for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
79        ;
80      _setmaxstdio (orig_max_stdio);
81      dtablesize = bound;
82    }
83  return dtablesize;
84}
85
86#endif
87