gsasl  1.10.0
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getdtablesize.c
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1 /* getdtablesize() function: Return maximum possible file descriptor value + 1.
2  Copyright (C) 2008-2021 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
33 _setmaxstdio_nothrow (int newmax)
34 {
35  int result;
36 
38  {
39  result = _setmaxstdio (newmax);
40  }
42  {
43  result = -1;
44  }
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
58 getdtablesize (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
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
#define RLIM_SAVED_CUR
Definition: getdtablesize.c:96
#define RLIM_SAVED_MAX
Definition: getdtablesize.c:99
int getdtablesize(void)
#define CATCH_MSVC_INVAL
Definition: msvc-inval.h:214
#define DONE_MSVC_INVAL
Definition: msvc-inval.h:216
#define TRY_MSVC_INVAL
Definition: msvc-inval.h:210