1/* getdtablesize() function: Return maximum possible file descriptor value + 1.
2   Copyright (C) 2008-2020 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 <https://www.gnu.org/licenses/>.  */
17
18#include <config.h>
19
20/* Specification.  */
21#include <unistd.h>
22
23#if defined _WIN32 && ! defined __CYGWIN__
24
25# include <stdio.h>
26
27# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
28#  include "msvc-inval.h"
29# endif
30
31# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
32static int
33_setmaxstdio_nothrow (int newmax)
34{
35  int result;
36
37  TRY_MSVC_INVAL
38    {
39      result = _setmaxstdio (newmax);
40    }
41  CATCH_MSVC_INVAL
42    {
43      result = -1;
44    }
45  DONE_MSVC_INVAL;
46
47  return result;
48}
49# else
50#  define _setmaxstdio_nothrow _setmaxstdio
51# endif
52
53/* Cache for the previous getdtablesize () result.  Safe to cache because
54   Windows also lacks setrlimit.  */
55static int dtablesize;
56
57int
58getdtablesize (void)
59{
60  if (dtablesize == 0)
61    {
62      /* We are looking for the number N such that the valid file descriptors
63         are 0..N-1.  It can be obtained through a loop as follows:
64           {
65             int fd;
66             for (fd = 3; fd < 65536; fd++)
67               if (dup2 (0, fd) == -1)
68                 break;
69             return fd;
70           }
71         On Windows XP, the result is 2048.
72         The drawback of this loop is that it allocates memory for a libc
73         internal array that is never freed.
74
75         The number N can also be obtained as the upper bound for
76         _getmaxstdio ().  _getmaxstdio () returns the maximum number of open
77         FILE objects.  The sanity check in _setmaxstdio reveals the maximum
78         number of file descriptors.  This too allocates memory, but it is
79         freed when we call _setmaxstdio with the original value.  */
80      int orig_max_stdio = _getmaxstdio ();
81      unsigned int bound;
82      for (bound = 0x10000; _setmaxstdio_nothrow (bound) < 0; bound = bound / 2)
83        ;
84      _setmaxstdio_nothrow (orig_max_stdio);
85      dtablesize = bound;
86    }
87  return dtablesize;
88}
89
90#else
91
92# include <limits.h>
93# include <sys/resource.h>
94
95# ifndef RLIM_SAVED_CUR
96#  define RLIM_SAVED_CUR RLIM_INFINITY
97# endif
98# ifndef RLIM_SAVED_MAX
99#  define RLIM_SAVED_MAX RLIM_INFINITY
100# endif
101
102# ifdef __CYGWIN__
103  /* Cygwin 1.7.25 auto-increases the RLIMIT_NOFILE soft limit until it
104     hits the compile-time constant hard limit of 3200.  We might as
105     well just report the hard limit.  */
106#  define rlim_cur rlim_max
107# endif
108
109int
110getdtablesize (void)
111{
112  struct rlimit lim;
113
114  if (getrlimit (RLIMIT_NOFILE, &lim) == 0
115      && 0 <= lim.rlim_cur && lim.rlim_cur <= INT_MAX
116      && lim.rlim_cur != RLIM_INFINITY
117      && lim.rlim_cur != RLIM_SAVED_CUR
118      && lim.rlim_cur != RLIM_SAVED_MAX)
119    return lim.rlim_cur;
120
121  return INT_MAX;
122}
123
124#endif
125