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From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: What do you do after you've done select(2)?
Message-ID: <1991May3.174432.1133@jpl-devvax.jpl.nasa.gov>
Date: 3 May 91 17:44:32 GMT
References: <1180015@hpcc01.HP.COM>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 32

In article <1180015@hpcc01.HP.COM> okamoto@hpcc01.HP.COM (Jeff Okamoto) writes:
: I have a question about the select(2) emulation in perl.
: 
: There are plenty of places that explain how to set up for the call to
: select, using fileno and vec to build the bitmap.  What those same examples
: DON'T provide is a good way to determine which file handle(s) are ready for
: each operation.
: 
: One way that I have seen, after going back through the archives is to keep
: an associative array with the names of the file handles and their fileno()
: values.  What I am wondering is, is there a better way?

It depends on how many filehandles you're managing.  For a few filehandles,
polling the vector from an associative array is probably reasonable.
For lots of filehandles, I'd make a back-translation table:

	$handle[fileno(STDOUT)] = 'STDOUT';

and then I'd unpack the vector and search it:

	$nfound = select($rout = $rin, $wout = $win, $xout = $xin, $timeout);
	$bits = unpack('b256', $rout);
	for ($fd = index($bits,'1'); $fd >= 0; $fd = index($bits,'1',$fd+1)) {
	    $handle = $handle[$fd];
	    if (defined $handle) {
		# do input using indirect filehandle or type glob
	    }
	}

and similarly for $wout and $xout.

Larry