I'm working on a little server that tails a file and listens to socket connections to which it relays info about that file. I've been playing around with doing non-blocking reads from both the filehandle and the socket, using IO::Select. Or rather, "semi-blocking" in that I want don't want to block on any particular handle, but I do want to block when there's nothing on any handle to keep CPU usage down.

So, I push my handles into the IO::Select object and supposedly both IO::Select->can_read() and IO::Select->select($handles, undef, undef, 0) are supposed to block until any one of the handles has some data, e.g.: 

    can_read ( [ TIMEOUT ] )
        Return an array of handles that are ready for reading. "TIMEOU
+T" is
        the maximum amount of time to wait before returning an empty l
+ist,
        in seconds, possibly fractional. If "TIMEOUT" is not given and
+ any
        handles are registered then the call will block.

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But when I try this, it doesn't block on the filehandle, and keeps looping with no new data in the file. Here is my sample minimal code where I am only working with the file handle and no TCP sockets: 

#!/usr/bin/perl
use IO::Select;

open $fh, '/tmp/test_file';
$sel = new IO::Select( $fh );

while(@ready = $sel->can_read) {
    print "looping\n";
    foreach $h (@ready) {
        if ($h == $fh) {
            print "reading from fh\n";
            while ($buf = <$h>) {
                print $loop++," $buf";
            }
        } else {
            print "handle is unknown\n";
        }
    }
}

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This tails my file just fine, but it doesn't block when the file is not changing. Any suggestions?

(I do know about File::Tail, in case anyone was going to suggest that, but I couldn't see how to implement it non-blocking and integrate that with the socket listener.)

Thanks.

In reply to blocking, non-blocking, and semi-blocking by genecutl

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