+ 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)
+ break;
+ 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;