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annotate lib/getdtablesize.c @ 12421:e8d2c6fc33ad

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Use spaces for indentation, not tabs.
author Bruno Haible <bruno@clisp.org>
date Thu, 10 Dec 2009 20:28:30 +0100
parents 729b89da65db
children c2cbabec01dd
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 /* getdtablesize() function for platforms that don't have it.
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2 Copyright (C) 2008-2009 Free Software Foundation, Inc.
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3 Written by Bruno Haible <bruno@clisp.org>, 2008.
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4
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5 This program is free software: you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 3 of the License, or
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8 (at your option) any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
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17
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18 #include <config.h>
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19
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20 /* Specification. */
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21 #include <unistd.h>
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22
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23 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
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24
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25 #include <stdio.h>
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26
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27 /* Cache for the previous getdtablesize () result. */
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28 static int dtablesize;
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29
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30 int
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31 getdtablesize (void)
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32 {
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33 if (dtablesize == 0)
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34 {
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35 /* We are looking for the number N such that the valid file descriptors
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36 are 0..N-1. It can be obtained through a loop as follows:
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37 {
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38 int fd;
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39 for (fd = 3; fd < 65536; fd++)
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40 if (dup2 (0, fd) == -1)
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41 break;
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42 return fd;
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43 }
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44 On Windows XP, the result is 2048.
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45 The drawback of this loop is that it allocates memory for a libc
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46 internal array that is never freed.
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47
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48 The number N can also be obtained as the upper bound for
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49 _getmaxstdio (). _getmaxstdio () returns the maximum number of open
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50 FILE objects. The sanity check in _setmaxstdio reveals the maximum
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51 number of file descriptors. This too allocates memory, but it is
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52 freed when we call _setmaxstdio with the original value. */
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53 int orig_max_stdio = _getmaxstdio ();
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54 unsigned int bound;
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55 for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
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56 ;
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57 _setmaxstdio (orig_max_stdio);
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58 dtablesize = bound;
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59 }
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60 return dtablesize;
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61 }
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62
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63 #endif