a11fb1dafc
* because it is not referentially transparent; normally we reserved parens for side-effecting code but given how people thoughtlessly close over it we revised that that decision for sender * caller can still omit parens
80 lines
3 KiB
ReStructuredText
80 lines
3 KiB
ReStructuredText
|
||
.. _scheduler-scala:
|
||
|
||
###################
|
||
Scheduler
|
||
###################
|
||
|
||
Sometimes the need for making things happen in the future arises, and where do
|
||
you go look then? Look no further than ``ActorSystem``! There you find the
|
||
:meth:`scheduler` method that returns an instance of
|
||
:class:`akka.actor.Scheduler`, this instance is unique per ActorSystem and is
|
||
used internally for scheduling things to happen at specific points in time.
|
||
|
||
You can schedule sending of messages to actors and execution of tasks
|
||
(functions or Runnable). You will get a ``Cancellable`` back that you can call
|
||
:meth:`cancel` on to cancel the execution of the scheduled operation.
|
||
|
||
.. warning::
|
||
|
||
The default implementation of ``Scheduler`` used by Akka is based on job
|
||
buckets which are emptied according to a fixed schedule. It does not
|
||
execute tasks at the exact time, but on every tick, it will run everything
|
||
that is (over)due. The accuracy of the default Scheduler can be modified
|
||
by the ``akka.scheduler.tick-duration`` configuration property.
|
||
|
||
Some examples
|
||
-------------
|
||
|
||
.. includecode:: code/docs/actor/SchedulerDocSpec.scala
|
||
:include: imports1,schedule-one-off-message
|
||
|
||
.. includecode:: code/docs/actor/SchedulerDocSpec.scala
|
||
:include: schedule-one-off-thunk
|
||
|
||
.. includecode:: code/docs/actor/SchedulerDocSpec.scala
|
||
:include: schedule-recurring
|
||
|
||
.. warning::
|
||
|
||
If you schedule functions or Runnable instances you should be extra careful
|
||
to not close over unstable references. In practice this means not using ``this``
|
||
inside the closure in the scope of an Actor instance, not accessing ``sender()`` directly
|
||
and not calling the methods of the Actor instance directly. If you need to
|
||
schedule an invocation schedule a message to ``self`` instead (containing the
|
||
necessary parameters) and then call the method when the message is received.
|
||
|
||
From ``akka.actor.ActorSystem``
|
||
-------------------------------
|
||
|
||
.. includecode:: ../../../akka-actor/src/main/scala/akka/actor/ActorSystem.scala
|
||
:include: scheduler
|
||
|
||
|
||
The Scheduler interface
|
||
-----------------------
|
||
|
||
The actual scheduler implementation is loaded reflectively upon
|
||
:class:`ActorSystem` start-up, which means that it is possible to provide a
|
||
different one using the ``akka.scheduler.implementation`` configuration
|
||
property. The referenced class must implement the following interface:
|
||
|
||
.. includecode:: ../../../akka-actor/src/main/scala/akka/actor/Scheduler.scala
|
||
:include: scheduler
|
||
|
||
The Cancellable interface
|
||
-------------------------
|
||
|
||
Scheduling a task will result in a :class:`Cancellable` (or throw an
|
||
:class:`IllegalStateException` if attempted after the scheduler’s shutdown).
|
||
This allows you to cancel something that has been scheduled for execution.
|
||
|
||
.. warning::
|
||
|
||
This does not abort the execution of the task, if it had already been
|
||
started. Check the return value of ``cancel`` to detect whether the
|
||
scheduled task was canceled or will (eventually) have run.
|
||
|
||
.. includecode:: ../../../akka-actor/src/main/scala/akka/actor/Scheduler.scala
|
||
:include: cancellable
|
||
|