Xref: utzoo comp.lang.c:12592 comp.unix.questions:9205
Path: utzoo!attcan!uunet!island!walker
From: walker@island.uu.net (Richard Walker)
Newsgroups: comp.lang.c,comp.unix.questions
Subject: Re: how many file descriptors?
Message-ID: <360@island.uu.net>
Date: 14 Sep 88 18:21:45 GMT
References: <24889@teknowledge-vaxc.ARPA>
Reply-To: walker@island.uu.net (Richard Walker)
Organization: Island Graphics, Marin County, California
Lines: 43

In article <24889@teknowledge-vaxc.ARPA> mkhaw@teknowledge-vaxc.UUCP (Mike Khaw) writes:
>How can a SunView program tell how many file descriptors it has in use,
>especially if it opens&closes /dev/fb several times and creates&destroys
>frames several times while it's running?
>Thanks,
>Mike Khaw

This is one of the things I hate about the Unix/Sunview combination.
Sunview uses file descriptors for its user interface objects yet
provides no control over allocation and release.
(They do get released *eventually* after the destruction).
Here are functions to determine the number of free file descriptors.

free_file_descriptors()
{
    int i, n;
    struct stat     statb;
    extern int      errno;

    /*  There is a slop factor of 2 in the fd calculations
	becuse the window system uses fd's transiently  */

    n = getdtablesize();
    for (i = n-1; i >= 0; i--)
	if (!(fstat(i, &statb) < 0 && errno == EBADF))
	    n--;
    /* RJW reserve SunView slop of 2 and 2 for prompt dialog */
    return(n-4);
}

/*
 * Return a flag indicating that there are 'n' free descriptors.
 */
enough_fds(n)
int n;
{
    if(n > free_file_descriptors()) {
	err_prompt("There are too many panels open.\n\
Please close some panels and try again.");
	return(0);
    }
    return(1);
}