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125 lines
3.4 KiB
C
125 lines
3.4 KiB
C
/* getdtablesize() function: Return maximum possible file descriptor value + 1.
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Copyright (C) 2008-2022 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2008.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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/* Specification. */
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#include <unistd.h>
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#if defined _WIN32 && ! defined __CYGWIN__
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# include <stdio.h>
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# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
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# include "msvc-inval.h"
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# endif
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# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
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static int
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_setmaxstdio_nothrow (int newmax)
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{
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int result;
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TRY_MSVC_INVAL
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{
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result = _setmaxstdio (newmax);
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}
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CATCH_MSVC_INVAL
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{
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result = -1;
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}
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DONE_MSVC_INVAL;
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return result;
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}
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# else
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# define _setmaxstdio_nothrow _setmaxstdio
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# endif
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/* Cache for the previous getdtablesize () result. Safe to cache because
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Windows also lacks setrlimit. */
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static int dtablesize;
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int
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getdtablesize (void)
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{
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if (dtablesize == 0)
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{
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/* We are looking for the number N such that the valid file descriptors
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are 0..N-1. It can be obtained through a loop as follows:
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{
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int fd;
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for (fd = 3; fd < 65536; fd++)
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if (dup2 (0, fd) == -1)
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break;
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return fd;
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}
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On Windows XP, the result is 2048.
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The drawback of this loop is that it allocates memory for a libc
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internal array that is never freed.
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The number N can also be obtained as the upper bound for
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_getmaxstdio (). _getmaxstdio () returns the maximum number of open
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FILE objects. The sanity check in _setmaxstdio reveals the maximum
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number of file descriptors. This too allocates memory, but it is
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freed when we call _setmaxstdio with the original value. */
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int orig_max_stdio = _getmaxstdio ();
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unsigned int bound;
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for (bound = 0x10000; _setmaxstdio_nothrow (bound) < 0; bound = bound / 2)
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;
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_setmaxstdio_nothrow (orig_max_stdio);
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dtablesize = bound;
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}
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return dtablesize;
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}
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#else
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# include <limits.h>
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# include <sys/resource.h>
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# ifndef RLIM_SAVED_CUR
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# define RLIM_SAVED_CUR RLIM_INFINITY
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# endif
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# ifndef RLIM_SAVED_MAX
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# define RLIM_SAVED_MAX RLIM_INFINITY
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# endif
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# ifdef __CYGWIN__
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/* Cygwin 1.7.25 auto-increases the RLIMIT_NOFILE soft limit until it
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hits the compile-time constant hard limit of 3200. We might as
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well just report the hard limit. */
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# define rlim_cur rlim_max
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# endif
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int
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getdtablesize (void)
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{
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struct rlimit lim;
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if (getrlimit (RLIMIT_NOFILE, &lim) == 0
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&& 0 <= lim.rlim_cur && lim.rlim_cur <= INT_MAX
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&& lim.rlim_cur != RLIM_INFINITY
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&& lim.rlim_cur != RLIM_SAVED_CUR
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&& lim.rlim_cur != RLIM_SAVED_MAX)
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return lim.rlim_cur;
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return INT_MAX;
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}
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#endif
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