1 files changed, 124 insertions, 0 deletions
diff --git a/lib/getdtablesize.c b/lib/getdtablesize.c
new file mode 100644
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--- /dev/null
+++ b/lib/getdtablesize.c
@@ -0,0 +1,124 @@
+/* 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