1/* getdtablesize() function for platforms that don't have it. 2 Copyright (C) 2008-2014 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 30static 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. */ 52static int dtablesize; 53 54int 55getdtablesize (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 92int 93rpl_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#endif 108