http://qs321.pair.com?node_id=859287

Eyck has asked for the wisdom of the Perl Monks concerning the following question:

I'm using following code: 
        $inotify->watch ($watchdir, IN_ALL_EVENTS) or die "watch creat
+ion failed" ;
        $0="cping: watch ready, waiting for activity (".scalar(localti
+me()).")...";
        my @events = $inotify->read;

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the line $inotify->read; is blocking, which is nice, since it doesn't burn CPU when there is nothing to do. But, now I need to run code, when there was no activity for longer then $timelimit; I could switch to non-blocking calls, ie use something like this: 
 $inotify->blocking(0);
 ...
 $inotify->read;
 sleep 1s;
 if ($idle>$timelimit) {
   code();
 };

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but then my code starts burning CPU AND becomes less responsive ( blocking code has much better then a 1 second latency with reacting to activity in $watchdir ). Is there any way out?

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Re: Blocking call with time limit ( Linux::Inotify2 )
by BrowserUk (Patriarch) on Sep 08, 2010 at 09:03 UTC

    The simple solution is Time::HiRes: 

    use Time::HiRes qw[ time sleep ];
...
$inotify->blocking(0);

my $end = time() + $timelimit;
while( time() < $end ) {
    for my $event ( $inotify->read ) {
        ## process event.
    }
    sleep 0.01; ## or 0.001 per your latency requirements
}

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    As for your fears about cpu usage. Polling once every hundredth or thousandth of a second, (much less every second), barely raises the usage at all. On my system, the usage is not discernible from zero to 2 decimal places.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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[d/l]
Re: Blocking call with time limit ( Linux::Inotify2 )
by Corion (Patriarch) on Sep 08, 2010 at 08:56 UTC

    I'm not sure whether the API for Linux::Inotify2 allows for a timeout.

    Before entering into the melee of signals or threads, I would look at the AnyEvent integration of Linux::Inotify2, maybe AnyEvent::Filesys::Notify. Using something like AnyEvent will turn parts of your program inside out, as you will get callbacks instead of actively check on things yourself.

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