lib/getdtablesize.c

   1 /* getdtablesize() function for platforms that don't have it.
   2    Copyright (C) 2008-2015 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 #elif HAVE_GETDTABLESIZE
  88
  89 # include <sys/resource.h>
  90 # undef getdtablesize
  91
  92 int
  93 rpl_getdtablesize(void)
  94 {
  95   /* To date, this replacement is only compiled for Cygwin 1.7.25,
  96      which auto-increased the RLIMIT_NOFILE soft limit until it
  97      hits the compile-time constant hard limit of 3200.  Although
  98      that version of cygwin supported a child process inheriting
  99      a smaller soft limit, the smaller limit is not enforced, so
 100      we might as well just report the hard limit.  */
 101   struct rlimit lim;
 102   if (!getrlimit (RLIMIT_NOFILE, &lim) && lim.rlim_max != RLIM_INFINITY)
 103     return lim.rlim_max;
 104   return getdtablesize ();
 105 }
 106
 107 #elif defined _SC_OPEN_MAX
 108
 109 int
 110 getdtablesize (void)
 111 {
 112   return sysconf (_SC_OPEN_MAX);
 113 }
 114
 115 #endif