| 1 | /* getdtablesize() function: Return maximum possible file descriptor value + 1.
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| 2 | Copyright (C) 2008-2021 Free Software Foundation, Inc.
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| 3 | Written by Bruno Haible <bruno@clisp.org>, 2008.
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| 4 |
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| 5 | This file is free software: you can redistribute it and/or modify
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| 6 | it under the terms of the GNU Lesser General Public License as
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| 7 | published by the Free Software Foundation; either version 2.1 of the
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| 8 | License, or (at your option) any later version.
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| 9 |
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| 10 | This file is distributed in the hope that it will be useful,
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | GNU Lesser General Public License for more details.
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| 14 |
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| 15 | You should have received a copy of the GNU Lesser General Public License
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| 16 | along with this program. If not, see <https://www.gnu.org/licenses/>. */
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| 17 |
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| 18 | #include <config.h>
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| 19 |
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| 20 | /* Specification. */
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| 21 | #include <unistd.h>
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| 22 |
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| 23 | #if defined _WIN32 && ! defined __CYGWIN__
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| 24 |
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| 25 | # include <stdio.h>
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| 26 |
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| 27 | # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
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| 28 | # include "msvc-inval.h"
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| 29 | # endif
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| 30 |
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| 31 | # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
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| 32 | static int
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| 33 | _setmaxstdio_nothrow (int newmax)
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| 34 | {
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| 35 | int result;
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| 36 |
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| 37 | TRY_MSVC_INVAL
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| 38 | {
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| 39 | result = _setmaxstdio (newmax);
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| 40 | }
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| 41 | CATCH_MSVC_INVAL
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| 42 | {
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| 43 | result = -1;
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| 44 | }
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| 45 | DONE_MSVC_INVAL;
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| 46 |
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| 47 | return result;
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| 48 | }
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| 49 | # else
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| 50 | # define _setmaxstdio_nothrow _setmaxstdio
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| 51 | # endif
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| 52 |
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| 53 | /* Cache for the previous getdtablesize () result. Safe to cache because
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| 54 | Windows also lacks setrlimit. */
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| 55 | static int dtablesize;
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| 56 |
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| 57 | int
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| 58 | getdtablesize (void)
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| 59 | {
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| 60 | if (dtablesize == 0)
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| 61 | {
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| 62 | /* We are looking for the number N such that the valid file descriptors
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| 63 | are 0..N-1. It can be obtained through a loop as follows:
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| 64 | {
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| 65 | int fd;
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| 66 | for (fd = 3; fd < 65536; fd++)
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| 67 | if (dup2 (0, fd) == -1)
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| 68 | break;
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| 69 | return fd;
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| 70 | }
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| 71 | On Windows XP, the result is 2048.
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| 72 | The drawback of this loop is that it allocates memory for a libc
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| 73 | internal array that is never freed.
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| 74 |
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| 75 | The number N can also be obtained as the upper bound for
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| 76 | _getmaxstdio (). _getmaxstdio () returns the maximum number of open
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| 77 | FILE objects. The sanity check in _setmaxstdio reveals the maximum
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| 78 | number of file descriptors. This too allocates memory, but it is
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| 79 | freed when we call _setmaxstdio with the original value. */
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| 80 | int orig_max_stdio = _getmaxstdio ();
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| 81 | unsigned int bound;
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| 82 | for (bound = 0x10000; _setmaxstdio_nothrow (bound) < 0; bound = bound / 2)
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| 83 | ;
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| 84 | _setmaxstdio_nothrow (orig_max_stdio);
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| 85 | dtablesize = bound;
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| 86 | }
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| 87 | return dtablesize;
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| 88 | }
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| 89 |
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| 90 | #else
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| 91 |
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| 92 | # include <limits.h>
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| 93 | # include <sys/resource.h>
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| 94 |
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| 95 | # ifndef RLIM_SAVED_CUR
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| 96 | # define RLIM_SAVED_CUR RLIM_INFINITY
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| 97 | # endif
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| 98 | # ifndef RLIM_SAVED_MAX
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| 99 | # define RLIM_SAVED_MAX RLIM_INFINITY
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| 100 | # endif
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| 101 |
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| 102 | # ifdef __CYGWIN__
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| 103 | /* Cygwin 1.7.25 auto-increases the RLIMIT_NOFILE soft limit until it
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| 104 | hits the compile-time constant hard limit of 3200. We might as
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| 105 | well just report the hard limit. */
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| 106 | # define rlim_cur rlim_max
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| 107 | # endif
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| 108 |
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| 109 | int
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| 110 | getdtablesize (void)
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| 111 | {
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| 112 | struct rlimit lim;
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| 113 |
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| 114 | if (getrlimit (RLIMIT_NOFILE, &lim) == 0
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| 115 | && 0 <= lim.rlim_cur && lim.rlim_cur <= INT_MAX
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| 116 | && lim.rlim_cur != RLIM_INFINITY
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| 117 | && lim.rlim_cur != RLIM_SAVED_CUR
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| 118 | && lim.rlim_cur != RLIM_SAVED_MAX)
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| 119 | return lim.rlim_cur;
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| 120 |
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| 121 | return INT_MAX;
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| 122 | }
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| 123 |
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| 124 | #endif
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