Re: Parallel processing, part two: event driven ? (some thoughts)

From: Dmitry Karasik <>
Date: 28 Sep 2005 10:33:40 +0200

        Hi lanas!

On 27 Sep 05 at 23:13, "lanas" (lanas ) wrote:

 lanas> Now, if several such tasks are to be performed in sequence, what
 lanas> approach would you recommend ? As far as I can see there are the
 lanas> Prima::Timer which looks like a crude approach but could
 lanas> nevertheless work I think, and there's the Prima::EventHook about
 lanas> which I there are no examples in the Prima example files.

I don't think Timer is needed here. Whenever you detect a EOF, you assume
that a process is finished and start a next one. For example:

  sub feed_batch
      close F;
      return unless $_ = shift @batch;
      open F, "$_|" or die $!;

  Prima::File-> new(
  file => feed_batch,
  onRead => sub {
     my $buffer;
     my $read = sysread( $_[0]-> file, $buffer, 512);
     if ( defined $read and $read > 0) {
        # do something with $buffer
     } elsif ( !defined $read) {
        # signal an error
     } else {
        # assume a process is finished, start a new one
        $_[0]-> file( feed_batch);
  } );

This is crude, but I think should be illustrative enough.

 lanas> But then the Prima::EventHook interface looks very interesting.
 lanas> Is it possible to create our own events and is it possible to set
 lanas> them in one way or another and expect the 'callback' (i.e. state
 lanas> manager) to immediately react upon ? How does it work exactly, any
 lanas> examples around ?

Yes, it is definitely possible to create our own events, it is done by
overloading the ::notification_types method. All of these events are
synchronous though; this means that you don't really need the event
dispatcher to signal anything you trigger yourself, a simple callback sub
would be enough. If you need asychnronous event dispatching, there is
onPostMessage, that is called after ::post_message.

There's no examples on EventHook, but there's short pod section in the
module, try perldoc Prima::EventHook.

	Dmitry Karasik
Received on Wed 28 Sep 2005 - 10:33:43 CEST

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