Manual Reference Pages - PADRE::TASKMANAGER (3)
Padre::TaskManager - Padre Background Task and Service Manager
The <B>Padre Task ManagerB> is responsible for scheduling, queueing and
executing all operations that do not occur in the main application thead.
While there is rarely any need for code elsewhere in Padre or a plugin to make
calls to this API, documentation is included for maintenance purposes.
It spawns and manages a pool of workers which act as containers for the
execution of standalone serialisable tasks. This execution model is based
loosely on the CPAN Process API, and involves the parent process creating
Padre::Task objects representing the work to do. These tasks are serialised
to a bytestream, passed down a shared queue to an appropriate worker,
deserialised back into an object, executed, and then reserialised for
transmission back to the parent thread.
Tasks operate on a shared-nothing basis. Each worker is required to
reload any modules needed by the task, and the task cannot access any of the
data structures. To compensate for these limits, tasks are able to send messages
back and forth between the instance of the task object in the parent and
the instance of the same task in the child.
Using this messaging channel, a task object in the child can send status
message or incremental results up to the parent, and the task object in the
parent can make changes to the GUI based on these messages.
The same messaging channel allows a background task to be cancelled elegantly
by the parent, although support for the cancel message is voluntary on
the part of the background task.
Services are implemented via the Padre::Service API. This is nearly
identical to, and sub-classes directly, the Padre::Task API.
The main difference between a task and a service is that a service will be
allocated a private, unused and dedicated worker that has never been
used by a task. Further, workers allocated to services will also not be counted
against the maximum workers limit.
my $manager = Padre::TaskManager->new(
conduit => $message_conduit,
The new constructor creates a new Task Manager instance. While it is
theoretically possible to create more than one instance, in practice this
is never likely to occur.
The constructor has a single compulsory parameter, which is an object that
implements the message conduit role Padre::Wx::Role::Conduit.
The message conduit is an object which provides direct integration with the
underlying child-to-parent messaging pipeline, which in Padre is done via
Wx::PlThreadEvent thread events.
Because the message conduit is provided to the constructor, the Task Manager
itself is able to function with no Wx-specific code whatsoever. This
simplifies implementation, allows sophisticated test rigs to be created,
and makes it easier for us to spin off the Task Manager as a some notional
standalone CPAN module.
The active accessor returns true if the task manager is currently running,
or false if not. Generally task manager startup will occur relatively early
in the Padre startup sequence, and task manager shutdown will occur relatively
early in the shutdown sequence (to prevent accidental task execution during
The maximum accessor returns the maximum quantity of worker threads that the
task manager will use for running ordinary finite-length tasks. Once the number
of active workers reaches the maximum limit, futher tasks will be pushed
onto a queue to wait for a free worker.
The start method bootstraps the task manager, creating the master thread.
The stop method shuts down the task manager, signalling active workers that
they should do an elegant shutdown.
The schedule method is used to give a task to the task manager and indicate
it should be run as soon as possible.
This may be immediately (with the task sent to a worker before the method
returns) or it may be delayed until some time in the future if all workers
As a convenience, this method returns true if the task could be dispatched
immediately, or false if it was queued for future execution.
$manager->cancelled( $owner );
The cancelled method is used with the task ownership feature of the
Padre::Task 3.0 API to signal tasks running in the background that
were created by a particular object that they should voluntarily abort as
their results are no longer wanted.
my $worker = $manager->start_worker;
The start_worker starts and returns a new registered Padre::TaskWorker
object, ready to execute a task or service in.
You generally should never need to call this method from outside
The stop_worker method shuts down a single worker, which (unfortunately) at
this time is indicated via the internal index position in the workers array.
The kill_worker method forcefully and immediately terminates a worker,
and like stop_worker the worker to kill is indicated by the internal
index position within the workers array.
<B>This method is not yet in use, the Task Manager does not current have the
ability to forcefully terminate workers.B>
The run method tells the Task Manager to sweep the queue of pending tasks
and dispatch as many as possible to worker threads.
Generally you should never need to call this method directly, as it will be
called whenever you schedule a task or when a worker becomes available.
Returns true if all pending tasks were dispatched, or false if any tasks
remain on the queue.
my $ok = $manager->good_task($task);
The good_task method takes a Padre::Task object and determines if the
task can be executed, given the resources available to the task manager.
Returns a Padre::Task object, or undef if there is no task to execute.
my $worker = $manager->best_worker( $task_object );
The best_worker method is used to find the best worker from the worker pool
for the execution of a particular task object.
This method makes use of a number of different strategies for optimising the
way in which workers are used, such as maximising worker reuse for the same
type of task, and specialising workers for particular types of tasks.
If all existing workers are in use this method may also spawn new workers,
up to the maximum worker limit. Without the slave master logic enabled this
will result in the editor blocking in the foreground briefly, this is something
we can live with until the slave master feature is working again.
Returns a Padre::TaskWorker object, or undef if there is no worker in
which the task can be run.
$manager->on_signal( \@message );
The on_signal method is called from the conduit object and acts as a
central distribution mechanism for messages coming from all child workers.
Messages arrive as a list of elements in an ARRAY with their first element
being the handle identifier of the Padre::TaskHandle for the task.
This envelope element is stripped from the front of the message, and the
remainder of the message is passed down into the handle (and the task within
Certain special messages, such as STARTED and STOPPED are emitted not by
the task but by the surrounding handle, and indicate to the task manager the
state of the child worker.
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.
|perl v5.20.3 ||PADRE::TASKMANAGER (3) ||2013-11-09 |
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