1 /* getdtablesize() function: Return maximum possible file descriptor value + 1.
2 Copyright (C) 2008-2023 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2008.
4
5 This file is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 2.1 of the
8 License, or (at your option) any later version.
9
10 This file 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 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser 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
32 static 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. */
55 static int dtablesize;
56
57 int
58 getdtablesize (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
109 int
110 getdtablesize (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