Commit a7b40bdb authored by Bruno Haible's avatar Bruno Haible
Browse files

Fix getdtablesize() on mingw.

parent 0aa929ca
2009-08-23 Bruno Haible <>
Fix getdtablesize() on mingw.
* lib/getdtablesize.c (getdtablesize): Implement differently.
* lib/ (getdtablesize): Improve comment.
2009-08-23 Bruno Haible <>
New module 'mkostemp'.
/* getdtablesize() function for platforms that don't have it.
Copyright (C) 2008 Free Software Foundation, Inc.
Copyright (C) 2008-2009 Free Software Foundation, Inc.
Written by Bruno Haible <>, 2008.
This program is free software: you can redistribute it and/or modify
......@@ -24,10 +24,40 @@
#include <stdio.h>
/* Cache for the previous getdtablesize () result. */
static int dtablesize;
getdtablesize (void)
return _getmaxstdio ();
if (dtablesize == 0)
/* We are looking for the number N such that the valid file descriptors
are 0..N-1. It can be obtained through a loop as follows:
int fd;
for (fd = 3; fd < 65536; fd++)
if (dup2 (0, fd) == -1)
return fd;
On Windows XP, the result is 2048.
The drawback of this loop is that it allocates memory for a libc
internal array that is never freed.
The number N can also be obtained as the upper bound for
_getmaxstdio (). _getmaxstdio () returns the maximum number of open
FILE objects. The sanity check in _setmaxstdio reveals the maximum
number of file descriptors. This too allocates memory, but it is
freed when we call _setmaxstdio with the original value. */
int orig_max_stdio = _getmaxstdio ();
unsigned int bound;
for (bound = 0x10000; _setmaxstdio (bound) < 0; bound = bound / 2)
_setmaxstdio (orig_max_stdio);
dtablesize = bound;
return dtablesize;
......@@ -328,7 +328,8 @@ extern int getdomainname(char *name, size_t len);
/* Return the maximum number of file descriptors in the current process. */
/* Return the maximum number of file descriptors in the current process.
In POSIX, this is same as sysconf (_SC_OPEN_MAX). */
extern int getdtablesize (void);
# endif
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