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Merge pull request #1611 from drewhk/wip-3167-illustration-actor-lifecycle-drewhk

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=doc #3167 Image clarifying paths, incarnations, UIDs, ActorRefs
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Roland Kuhn 2013-07-09 02:43:26 -07:00
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akka-docs/rst/java/untyped-actors.rst
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@ -241,6 +241,41 @@ described in the following:
The implementations shown above are the defaults provided by the :class:`UntypedActor`
class.
Actor Lifecycle
---------------
.. image:: ../images/actor_lifecycle.png
:align: center
:width: 680
A path in an actor system represents a "place" which might be occupied
by a living actor. Initially (apart from system initialized actors) a path is
empty. When ``actorOf()`` is called it assigns an *incarnation* of the actor
described by the passed ``Props`` to the given path. An actor incarnation is
identified by the path *and a UID*. A restart only swaps the ``Actor``
instance defined by the ``Props`` but the incarnation and hence the UID remains
the same.
The lifecycle of an incarnation ends when the actor is stopped. At
that point the appropriate lifecycle events are called and watching actors
are notified of the termination. After the incarnation is stopped, the path can
be reused again by creating an actor with ``actorOf()``. In this case the
name of the new incarnation will be the same as the previous one but the
UIDs will differ.
An ``ActorRef`` always represents an incarnation (path and UID) not just a
given path. Therefore if an actor is stopped and a new one with the same
name is created an ``ActorRef`` of the old incarnation will not point
to the new one.
``ActorSelection`` on the other hand points to the path (or multiple paths
if wildcards are used) and is completely oblivious to which incarnation is currently
occupying it. ``ActorSelection`` cannot be watched for this reason. It is
possible to resolve the current incarnation's ``ActorRef`` living under the
path by sending an ``Identify`` message to the ``ActorSelection`` which
will be replied to with an ``ActorIdentity`` containing the correct reference
(see :ref:`actorSelection-java`).
.. _deathwatch-java:
Lifecycle Monitoring aka DeathWatch