Async::MergePoint man page on Fedora

Man page or keyword search:  
man Server   31170 pages
apropos Keyword Search (all sections)
Output format
Fedora logo
[printable version]

Async::MergePoint(3)  User Contributed Perl Documentation Async::MergePoint(3)

NAME
       "Async::MergePoint" - resynchronise diverged control flow

SYNOPSIS
	use Async::MergePoint;

	my $merge = Async::MergePoint->new(
	   needs => [ "leaves", "water" ],
	);

	my $water;
	Kettle->boil(
	   on_boiled => sub { $water = shift; $merge->done( "water" ); }
	);

	my $tea_leaves;
	Cupboard->get_tea_leaves(
	   on_fetched => sub { $tea_leaves = shift; $merge->done( "leaves" ); }
	);

	$merge->close(
	   on_finished => sub {
	      # Make tea using $water and $tea_leaves
	   }
	);

DESCRIPTION
       Often in program logic, multiple different steps need to be taken that
       are independent of each other, but their total result is needed before
       the next step can be taken. In synchonous code, the usual approach is
       to do them sequentially.

       An asynchronous or event-based program could do this, but if each step
       involves some IO idle time, better overall performance can often be
       gained by running the steps in parallel. A "Async::MergePoint" object
       can then be used to wait for all of the steps to complete, before
       passing the combined result of each step on to the next stage.

       A merge point maintains a set of outstanding operations it is waiting
       on; these are arbitrary string values provided at the object's
       construction. Each time the "done()" method is called, the named item
       is marked as being complete. When all of the required items are so
       marked, the "on_finished" continuation is invoked.

       For use cases where code may be split across several different lexical
       scopes, it may not be convenient or possible to share a lexical
       variable, to pass on the result of some asynchronous operation. In
       these cases, when an item is marked as complete a value can also be
       provided which contains the results of that step. The "on_finished"
       callback is passed a hash (in list form, rather than by reference) of
       the collected item values.

       This module was originally part of the IO::Async distribution, but was
       removed under the inspiration of Pedro Melo's Async::Hooks
       distribution, because it doesn't itself contain anything IO-specific.

CONSTRUCTOR
   $merge = Async::MergePoint->new( %params )
       This function returns a new instance of a "Async::MergePoint" object.
       The %params hash takes the following keys:

       needs => ARRAY
	       Optional. An array containing unique item names to wait on. The
	       order of this array is not significant.

       on_finished => CODE
	       Optional. CODE reference to the continuation for when the merge
	       point becomes ready. If provided, will be passed to the "close"
	       method.

METHODS
   $merge->close( %params )
       Allows an "on_finished" continuation to be set if one was not provided
       to the constructor.

       on_finished => CODE
	       CODE reference to the continuation for when the merge point
	       becomes ready.

       The "on_finished" continuation will be called when every key in the
       "needs" list has been notified by the "done()" method. It will be
       called as

	$on_finished->( %items )

       where the %items hash will contain the item names that were waited on,
       and the values passed to the "done()" method for each one. Note that
       this is passed as a list, not as a HASH reference.

       While this feature can be used to pass data from the component parts
       back up into the continuation, it may be more direct to use normal
       lexical variables instead. This method allows the continuation to be
       placed after the blocks of code that execute the component parts, so it
       reads downwards, and may make it more readable.

   $merge->needs( @keys )
       When called on an open MergePoint (i.e. one that does not yet have an
       "on_finished" continuation), this method adds extra key names to the
       set of outstanding names. The order of this list is not significant.

       This method throws an exception if the MergePoint is already closed.

   $merge->done( $item, $value )
       This method informs the merge point that the $item is now ready, and
       passes it a value to store, to be passed into the "on_finished"
       continuation.  If this call gives the final remaining item being waited
       for, the "on_finished" continuation is called within it, and the method
       will not return until it has completed.

EXAMPLES
   Asynchronous Plugins
       Consider a program using "Module::Pluggable" to provide a plugin
       architecture to respond to events, where sometimes the response to an
       event may require asynchronous work. A "MergePoint" object can be used
       to coordinate the responses from the plugins to this event.

	my $merge = Async::MergePoint->new();

	foreach my $plugin ( $self->plugins ) {
	   $plugin->handle_event( "event", $merge, @args );
	}

	$merge->close( on_finished => sub {
	   my %results = @_;
	   print "All plugins have recognised $event\n";
	} );

       Each plugin that wishes to handle the event can use its own package
       name, for example, as its unique key name for the MergePoint. A plugin
       handling the event synchonously could perform something such as:

	sub handle_event
	{
	   my ( $event, $merge, @args ) = @_;
	   ....
	   $merge->needs( __PACKAGE__ );
	   $merge->done( __PACKAGE__ => $result );
	}

       Whereas, to handle the event asynchronously the plugin can instead
       perform:

	sub handle_event
	{
	   my ( $event, $merge, @args ) = @_;
	   ....
	   $merge->needs( __PACKAGE__ );

	   sometime_later( sub {
	      $merge->done( __PACKAGE__ => $result );
	   } );
	}

AUTHOR
       Paul Evans <leonerd@leonerd.org.uk>

perl v5.14.2			  2009-07-06		  Async::MergePoint(3)
[top]

List of man pages available for Fedora

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net