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067428c1 PE |
1 | /* getdtablesize() function for platforms that don't have it. |
2 | Copyright (C) 2008-2013 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 | |
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 |