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c0c3707f CB |
1 | /* getdtablesize() function: Return maximum possible file descriptor value + 1. |
2 | Copyright (C) 2008-2019 Free Software Foundation, Inc. | |
6ec2e0f5 SDJ |
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 | |
c0c3707f | 16 | along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
6ec2e0f5 SDJ |
17 | |
18 | #include <config.h> | |
19 | ||
20 | /* Specification. */ | |
21 | #include <unistd.h> | |
22 | ||
c0c3707f | 23 | #if defined _WIN32 && ! defined __CYGWIN__ |
6ec2e0f5 SDJ |
24 | |
25 | # include <stdio.h> | |
26 | ||
c0c3707f CB |
27 | # if HAVE_MSVC_INVALID_PARAMETER_HANDLER |
28 | # include "msvc-inval.h" | |
29 | # endif | |
6ec2e0f5 SDJ |
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 | } | |
c0c3707f CB |
49 | # else |
50 | # define _setmaxstdio_nothrow _setmaxstdio | |
6ec2e0f5 SDJ |
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; | |
c0c3707f | 82 | for (bound = 0x10000; _setmaxstdio_nothrow (bound) < 0; bound = bound / 2) |
6ec2e0f5 | 83 | ; |
c0c3707f | 84 | _setmaxstdio_nothrow (orig_max_stdio); |
6ec2e0f5 SDJ |
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 |