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      1 /* getdtablesize() function: Return maximum possible file descriptor value + 1.
      2    Copyright (C) 2008-2022 Free Software Foundation, Inc.
      3    Written by Bruno Haible <bruno (at) clisp.org>, 2008.
      4 
      5    This file is free software: you can redistribute it and/or modify
      6    it under the terms of the GNU Lesser General Public License as
      7    published by the Free Software Foundation; either version 2.1 of the
      8    License, or (at your option) any later version.
      9 
     10    This file 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 Lesser General Public License for more details.
     14 
     15    You should have received a copy of the GNU Lesser General Public License
     16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
     17 
     18 #include <config.h>
     19 
     20 /* Specification.  */
     21 #include <unistd.h>
     22 
     23 #if defined _WIN32 && ! defined __CYGWIN__
     24 
     25 # include <stdio.h>
     26 
     27 # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
     28 #  include "msvc-inval.h"
     29 # endif
     30 
     31 # if HAVE_MSVC_INVALID_PARAMETER_HANDLER
     32 static int
     33 _setmaxstdio_nothrow (int newmax)
     34 {
     35   int result;
     36 
     37   TRY_MSVC_INVAL
     38     {
     39       result = _setmaxstdio (newmax);
     40     }
     41   CATCH_MSVC_INVAL
     42     {
     43       result = -1;
     44     }
     45   DONE_MSVC_INVAL;
     46 
     47   return result;
     48 }
     49 # else
     50 #  define _setmaxstdio_nothrow _setmaxstdio
     51 # endif
     52 
     53 /* Cache for the previous getdtablesize () result.  Safe to cache because
     54    Windows also lacks setrlimit.  */
     55 static int dtablesize;
     56 
     57 int
     58 getdtablesize (void)
     59 {
     60   if (dtablesize == 0)
     61     {
     62       /* We are looking for the number N such that the valid file descriptors
     63          are 0..N-1.  It can be obtained through a loop as follows:
     64            {
     65              int fd;
     66              for (fd = 3; fd < 65536; fd++)
     67                if (dup2 (0, fd) == -1)
     68                  break;
     69              return fd;
     70            }
     71          On Windows XP, the result is 2048.
     72          The drawback of this loop is that it allocates memory for a libc
     73          internal array that is never freed.
     74 
     75          The number N can also be obtained as the upper bound for
     76          _getmaxstdio ().  _getmaxstdio () returns the maximum number of open
     77          FILE objects.  The sanity check in _setmaxstdio reveals the maximum
     78          number of file descriptors.  This too allocates memory, but it is
     79          freed when we call _setmaxstdio with the original value.  */
     80       int orig_max_stdio = _getmaxstdio ();
     81       unsigned int bound;
     82       for (bound = 0x10000; _setmaxstdio_nothrow (bound) < 0; bound = bound / 2)
     83         ;
     84       _setmaxstdio_nothrow (orig_max_stdio);
     85       dtablesize = bound;
     86     }
     87   return dtablesize;
     88 }
     89 
     90 #else
     91 
     92 # include <limits.h>
     93 # include <sys/resource.h>
     94 
     95 # ifndef RLIM_SAVED_CUR
     96 #  define RLIM_SAVED_CUR RLIM_INFINITY
     97 # endif
     98 # ifndef RLIM_SAVED_MAX
     99 #  define RLIM_SAVED_MAX RLIM_INFINITY
    100 # endif
    101 
    102 # ifdef __CYGWIN__
    103   /* Cygwin 1.7.25 auto-increases the RLIMIT_NOFILE soft limit until it
    104      hits the compile-time constant hard limit of 3200.  We might as
    105      well just report the hard limit.  */
    106 #  define rlim_cur rlim_max
    107 # endif
    108 
    109 int
    110 getdtablesize (void)
    111 {
    112   struct rlimit lim;
    113 
    114   if (getrlimit (RLIMIT_NOFILE, &lim) == 0
    115       && 0 <= lim.rlim_cur && lim.rlim_cur <= INT_MAX
    116       && lim.rlim_cur != RLIM_INFINITY
    117       && lim.rlim_cur != RLIM_SAVED_CUR
    118       && lim.rlim_cur != RLIM_SAVED_MAX)
    119     return lim.rlim_cur;
    120 
    121   return INT_MAX;
    122 }
    123 
    124 #endif
    125