lib/getdtablesize.c

   1 /* getdtablesize() function for platforms that don't have it.
   2    Copyright (C) 2008-2017 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2008.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 /* Specification.  */
  21 #include <unistd.h>
  22
  23 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  24
  25 # include <stdio.h>
  26
  27 # include "msvc-inval.h"
  28
  29 # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
  30 static int
  31 _setmaxstdio_nothrow (int newmax)
  32 {
  33   int result;
  34
  35   TRY_MSVC_INVAL
  36     {
  37       result = _setmaxstdio (newmax);
  38     }
  39   CATCH_MSVC_INVAL
  40     {
  41       result = -1;
  42     }
  43   DONE_MSVC_INVAL;
  44
  45   return result;
  46 }
  47 #  define _setmaxstdio _setmaxstdio_nothrow
  48 # endif
  49
  50 /* Cache for the previous getdtablesize () result.  Safe to cache because
  51    Windows also lacks setrlimit.  */
  52 static int dtablesize;
  53
  54 int
  55 getdtablesize (void)
  56 {
  57   if (dtablesize == 0)
  58     {
  59       /* We are looking for the number N such that the valid file descriptors
  60          are 0..N-1.  It can be obtained through a loop as follows:
  61            {
  62              int fd;
  63              for (fd = 3; fd < 65536; fd++)
  64                if (dup2 (0, fd) == -1)
  65                  break;
  66              return fd;
  67            }
  68          On Windows XP, the result is 2048.
  69          The drawback of this loop is that it allocates memory for a libc
  70          internal array that is never freed.
  71
  72          The number N can also be obtained as the upper bound for
  73          _getmaxstdio ().  _getmaxstdio () returns the maximum number of open
  74          FILE objects.  The sanity check in _setmaxstdio reveals the maximum
  75          number of file descriptors.  This too allocates memory, but it is
  76          freed when we call _setmaxstdio with the original value.  */
  77       int orig_max_stdio = _getmaxstdio ();
  78       unsigned int bound;
  79       for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
  80         ;
  81       _setmaxstdio (orig_max_stdio);
  82       dtablesize = bound;
  83     }
  84   return dtablesize;
  85 }
  86
  87 #else
  88
  89 # include <limits.h>
  90 # include <sys/resource.h>
  91
  92 # ifndef RLIM_SAVED_CUR
  93 #  define RLIM_SAVED_CUR RLIM_INFINITY
  94 # endif
  95 # ifndef RLIM_SAVED_MAX
  96 #  define RLIM_SAVED_MAX RLIM_INFINITY
  97 # endif
  98
  99 # ifdef __CYGWIN__
 100   /* Cygwin 1.7.25 auto-increases the RLIMIT_NOFILE soft limit until it
 101      hits the compile-time constant hard limit of 3200.  We might as
 102      well just report the hard limit.  */
 103 #  define rlim_cur rlim_max
 104 # endif
 105
 106 int
 107 getdtablesize (void)
 108 {
 109   struct rlimit lim;
 110
 111   if (getrlimit (RLIMIT_NOFILE, &lim) == 0
 112       && 0 <= lim.rlim_cur && lim.rlim_cur <= INT_MAX
 113       && lim.rlim_cur != RLIM_INFINITY
 114       && lim.rlim_cur != RLIM_SAVED_CUR
 115       && lim.rlim_cur != RLIM_SAVED_MAX)
 116     return lim.rlim_cur;
 117
 118   return INT_MAX;
 119 }
 120
 121 #endif