1/* getdtablesize() function for platforms that don't have it.
2   Copyright (C) 2008-2014 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.  Safe to cache because
51   Windows also lacks setrlimit.  */
52static int dtablesize;
53
54int
55getdtablesize (void)
56{
57  if (dtablesize == 0)
58    {
59      /* We are looking for the number N such that the valid file descriptors
60         are 0..N-1.  It can be obtained through a loop as follows:
61           {
62             int fd;
63             for (fd = 3; fd < 65536; fd++)
64               if (dup2 (0, fd) == -1)
65                 break;
66             return fd;
67           }
68         On Windows XP, the result is 2048.
69         The drawback of this loop is that it allocates memory for a libc
70         internal array that is never freed.
71
72         The number N can also be obtained as the upper bound for
73         _getmaxstdio ().  _getmaxstdio () returns the maximum number of open
74         FILE objects.  The sanity check in _setmaxstdio reveals the maximum
75         number of file descriptors.  This too allocates memory, but it is
76         freed when we call _setmaxstdio with the original value.  */
77      int orig_max_stdio = _getmaxstdio ();
78      unsigned int bound;
79      for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
80        ;
81      _setmaxstdio (orig_max_stdio);
82      dtablesize = bound;
83    }
84  return dtablesize;
85}
86
87#elif HAVE_GETDTABLESIZE
88
89# include <sys/resource.h>
90# undef getdtablesize
91
92int
93rpl_getdtablesize(void)
94{
95  /* To date, this replacement is only compiled for Cygwin 1.7.25,
96     which auto-increased the RLIMIT_NOFILE soft limit until it
97     hits the compile-time constant hard limit of 3200.  Although
98     that version of cygwin supported a child process inheriting
99     a smaller soft limit, the smaller limit is not enforced, so
100     we might as well just report the hard limit.  */
101  struct rlimit lim;
102  if (!getrlimit (RLIMIT_NOFILE, &lim) && lim.rlim_max != RLIM_INFINITY)
103    return lim.rlim_max;
104  return getdtablesize ();
105}
106
107#endif
108