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/* getdtablesize() function: Return maximum possible file descriptor value + 1.
Copyright (C) 2008-2024 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2008.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
This file is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include <unistd.h>
#if defined _WIN32 && ! defined __CYGWIN__
# include <stdio.h>
# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
# include "msvc-inval.h"
# endif
# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
static int
_setmaxstdio_nothrow (int newmax)
{
int result;
TRY_MSVC_INVAL
{
result = _setmaxstdio (newmax);
}
CATCH_MSVC_INVAL
{
result = -1;
}
DONE_MSVC_INVAL;
return result;
}
# else
# define _setmaxstdio_nothrow _setmaxstdio
# endif
/* Cache for the previous getdtablesize () result. Safe to cache because
Windows also lacks setrlimit. */
static int dtablesize;
int
getdtablesize (void)
{
if (dtablesize == 0)
{
/* We are looking for the number N such that the valid file descriptors
are 0..N-1. It can be obtained through a loop as follows:
{
int fd;
for (fd = 3; fd < 65536; fd++)
if (dup2 (0, fd) == -1)
break;
return fd;
}
On Windows XP, the result is 2048.
The drawback of this loop is that it allocates memory for a libc
internal array that is never freed.
The number N can also be obtained as the upper bound for
_getmaxstdio (). _getmaxstdio () returns the maximum number of open
FILE objects. The sanity check in _setmaxstdio reveals the maximum
number of file descriptors. This too allocates memory, but it is
freed when we call _setmaxstdio with the original value. */
int orig_max_stdio = _getmaxstdio ();
unsigned int bound;
for (bound = 0x10000; _setmaxstdio_nothrow (bound) < 0; bound = bound / 2)
;
_setmaxstdio_nothrow (orig_max_stdio);
dtablesize = bound;
}
return dtablesize;
}
#else
# include <limits.h>
# include <sys/resource.h>
# ifndef RLIM_SAVED_CUR
# define RLIM_SAVED_CUR RLIM_INFINITY
# endif
# ifndef RLIM_SAVED_MAX
# define RLIM_SAVED_MAX RLIM_INFINITY
# endif
# ifdef __CYGWIN__
/* Cygwin 1.7.25 auto-increases the RLIMIT_NOFILE soft limit until it
hits the compile-time constant hard limit of 3200. We might as
well just report the hard limit. */
# define rlim_cur rlim_max
# endif
int
getdtablesize (void)
{
struct rlimit lim;
if (getrlimit (RLIMIT_NOFILE, &lim) == 0
&& 0 <= lim.rlim_cur && lim.rlim_cur <= INT_MAX
&& lim.rlim_cur != RLIM_INFINITY
&& lim.rlim_cur != RLIM_SAVED_CUR
&& lim.rlim_cur != RLIM_SAVED_MAX)
return lim.rlim_cur;
return INT_MAX;
}
#endif
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