1 /* getdtablesize() function: Return maximum possible file descriptor value + 1. 2 Copyright (C) 2008-2020 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 <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 _setmaxstdio_nothrow(int newmax)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 getdtablesize(void)58getdtablesize (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 getdtablesize(void)110getdtablesize (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