NAME

       Padre::Role::Task - A role for objects that commission tasks

DESCRIPTION

       This is a role that should be inherited from by objects in Padre's permanent model that
       want to commision tasks to be run and have the results fed back to them, if the answer is
       still relevant.

   Task Revisions
       Objects in Padre that commission tasks to run in the background can continue processing
       and changing state during the queue'ing and/or execution of their background tasks.

       If the object state changes in such a way as to make the results of a background task
       irrelevant, a mechanism is needed to ensure these background tasks are aborted where
       possible, or their results thrown away when not.

       Padre::Role::Task provides the concept of "task revisions" to support this functionality.

       A task revision is an incrementing number for each owner that remains the same as long as
       the results from any arbitrary launched task remains relevant for the current state of the
       object.

       When an object transitions a state boundary it will increment it's revision, whether there
       are any running tasks or not.

       When a task has completed the task manager will look up the owner (if it has one) and
       check to see if the current revision of the owner object is the same as when the task was
       scheduled. If so the Task Manager will call the "on_finish" handler passing it the task.
       If not, the completed task will be silently discarded.

   Sending messages to your tasks
       The Padre::Task API supports bidirection communication between tasks and their owners.

       However, when you commission a task via "task_request" the task object is not returned,
       leaving you without access to the task and thus without a method by which to send messages
       to the child.

       This is intentional, as there is no guarentee that your task will be launched immediately
       and so sending messages immediately may be unsafe. The task may need to be delayed until a
       new background worker can be spawned, or for longer if the maximum background worker limit
       has been reached.

       The solution is provided by the "on_message" handler, which is passed the parent task
       object as its first parameter.

       Tasks which expect to be sent messages from their owner should send the owner a greeting
       message as soon as they have started. Not only does this let the parent know that work has
       commenced on their task, but it provides the task object to the owner once there is
       certainty that any parent messages can be dispatched to the child successfully.

       In the following example, we assume a long running "service" style task that will need to
       be interacted with over time.

         sub service_start {
             my $self = shift;

             $self->task_reset;
             $self->task_request(
                 task       => 'My::Service',
                 on_message => 'my_message',
                 on_finish  => 'my_finish',
             );
         }

         sub my_message {
             my $self = shift;
             my $task = shift;

             # In this example our task sends an empty message to indicate "started"
             unless ( @_ ) {
                 $self->{my_service} = $task;
                 return;
             }

             # Handle other messages...
         }

METHODS

   task_owner
         Padre::Role::Task->task_owner( 1234 );

       The "task_owner" static method is a convenience method which takes an owner id and will
       look up the owner object.

       Returns the object if it still exists and has not changed it's task revision.

       Returns "undef" of the owner object no longer exists, or has changed its task revision
       since the original owner id was issued.

   task_manager
       The "task_manager" method is a convenience for quick access to the Padre's
       Padre::TaskManager instance.

   task_revision
       The "task_revision" accessor returns the current task revision for an object.

   task_reset
       The "task_reset" method is called when the state of an owner object significantly changes,
       and outstanding tasks should be deleted or ignored.

       It will change the task revision of the owner and request the task manager to send a
       standard "cancel" message to any currently executing background tasks, allowing them to
       terminate elegantly (if they handle

   task_request
         $self->task_request(
             task       => 'Padre::Task::SomeTask',
             on_message => 'message_handler_method',
             on_finish  => 'finish_handler_method',
             my_param1  => 123,
             my_param2  => 'abc',
         );

       The "task_request" method is used to spawn a new background task for the owner, loading
       the class and registering for callback messages in the process.

       The "task" parameter indicates the class of the task to be executed, which must inherit
       from Padre::Task. The class itself will be automatically loaded if required.

       The optional "on_message" parameter should be the name of a method (which must exist if
       provided) that will receive owner-targetted messages from the background process.

       The method will be passed the task object (as it exists after the "prepare" phase in the
       parent thread) as its first parameter, followed by any values passed by the background
       task.

       If no "on_message" parameter is provided the default method null "task_message" will be
       called.

       The optional "on_finish" parameter should be the name of a method (which must exist if
       provided) that will receive the task object back from the background worker once the task
       has completed, complete with any state saved in the task during its background execution.

       It is passed a single parameter, which is the Padre::Task object.

       If no "on_finish" parameter is provided the default method null "task_finish" will be
       called.

       Any other parameters are passed through the constructor method of the task.

   task_finish
       The "task_finish" method is the default handler method for completed tasks, and will be
       called for any "task_request" where no specific "on_finish" handler was provided.

       If your object issues only one task, or if you would prefer a single common finish handler
       for all your different tasks, you should override this method instead of explicitly
       defining an "on_finish" handler for every task.

       The default implementation ensures that every task has an appropriate finish handler by
       throwing an exception with a message indicating the owner and task class for which no
       finish handler could be found.

   task_message
       The "task_message" method is the default handler method for completed tasks, and will be
       called for any "task_request" where no specific "on_message" handler was provided.

       If your object issues only one task, or if you would prefer a single common message
       handler for all your different tasks, you should override this method instead of
       explicitly defining an "on_finish" handler for every task.

       If none of your tasks will send messages back to their owner, you do not need to define
       this method.

       The default implementation ensures that every task has an appropriate finish handler by
       throwing an exception with a message indicating the owner and task class for which no
       finish handler could be found.

COPYRIGHT & LICENSE

       Copyright 2008-2013 The Padre development team as listed in Padre.pm.

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       The full text of the license can be found in the LICENSE file included with this module.