| 1 | /* getdtablesize() function for platforms that don't have it.
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| 2 | Copyright (C) 2008-2012 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 | #include "msvc-inval.h"
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| 28 |
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| 29 | #if HAVE_MSVC_INVALID_PARAMETER_HANDLER
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| 30 | static inline int
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| 31 | _setmaxstdio_nothrow (int newmax)
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| 32 | {
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| 33 | int result;
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| 34 |
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| 35 | TRY_MSVC_INVAL
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| 36 | {
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| 37 | result = _setmaxstdio (newmax);
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| 38 | }
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| 39 | CATCH_MSVC_INVAL
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| 40 | {
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| 41 | result = -1;
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| 42 | }
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| 43 | DONE_MSVC_INVAL;
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| 44 |
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| 45 | return result;
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| 46 | }
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| 47 | # define _setmaxstdio _setmaxstdio_nothrow
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| 48 | #endif
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| 49 |
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| 50 | /* Cache for the previous getdtablesize () result. */
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| 51 | static int dtablesize;
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| 52 |
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| 53 | int
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| 54 | getdtablesize (void)
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| 55 | {
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| 56 | if (dtablesize == 0)
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| 57 | {
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| 58 | /* We are looking for the number N such that the valid file descriptors
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| 59 | are 0..N-1. It can be obtained through a loop as follows:
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| 60 | {
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| 61 | int fd;
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| 62 | for (fd = 3; fd < 65536; fd++)
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| 63 | if (dup2 (0, fd) == -1)
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| 64 | break;
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| 65 | return fd;
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| 66 | }
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| 67 | On Windows XP, the result is 2048.
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| 68 | The drawback of this loop is that it allocates memory for a libc
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| 69 | internal array that is never freed.
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| 70 |
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| 71 | The number N can also be obtained as the upper bound for
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| 72 | _getmaxstdio (). _getmaxstdio () returns the maximum number of open
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| 73 | FILE objects. The sanity check in _setmaxstdio reveals the maximum
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| 74 | number of file descriptors. This too allocates memory, but it is
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| 75 | freed when we call _setmaxstdio with the original value. */
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| 76 | int orig_max_stdio = _getmaxstdio ();
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| 77 | unsigned int bound;
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| 78 | for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
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| 79 | ;
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| 80 | _setmaxstdio (orig_max_stdio);
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| 81 | dtablesize = bound;
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| 82 | }
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| 83 | return dtablesize;
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| 84 | }
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| 85 |
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| 86 | #endif
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