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+/* getdtablesize() function: Return maximum possible file descriptor value + 1.
+ Copyright (C) 2008-2022 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