1 /* getdtablesize() function for platforms that don't have it. 2 Copyright (C) 2008-2012 Free Software Foundation, Inc. 3 Written by Bruno Haible <bruno (at) 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. */ 51 static int dtablesize; 52 53 int 54 getdtablesize (void) 55 { 56 if (dtablesize == 0) 57 { 58 /* We are looking for the number N such that the valid file descriptors 59 are 0..N-1. It can be obtained through a loop as follows: 60 { 61 int fd; 62 for (fd = 3; fd < 65536; fd++) 63 if (dup2 (0, fd) == -1) 64 break; 65 return fd; 66 } 67 On Windows XP, the result is 2048. 68 The drawback of this loop is that it allocates memory for a libc 69 internal array that is never freed. 70 71 The number N can also be obtained as the upper bound for 72 _getmaxstdio (). _getmaxstdio () returns the maximum number of open 73 FILE objects. The sanity check in _setmaxstdio reveals the maximum 74 number of file descriptors. This too allocates memory, but it is 75 freed when we call _setmaxstdio with the original value. */ 76 int orig_max_stdio = _getmaxstdio (); 77 unsigned int bound; 78 for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2) 79 ; 80 _setmaxstdio (orig_max_stdio); 81 dtablesize = bound; 82 } 83 return dtablesize; 84 } 85 86 #endif 87
