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!clu #3617 API improvements related to CurrentClusterState

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* Getter for CurrentClusterState in Cluster extension, updated via
  ClusterReadView
* Remove lazy init of readView. Otherwise the cluster.state will be
  empty on first access, wich is probably surprising
* Subscribe to several cluster event types at once, to ensure *one*
  CurrentClusterEvent followed by change events
* Deprecate publishCurrentClusterState, was a bad idea, use sendCurrentClusterState
  instead
* Possibility to subscribe with InitialStateAsEvents to receive events corresponding
  to CurrentClusterState
* CurrentClusterState not a ClusterDomainEvent, ticket #3614
This commit is contained in:
Patrik Nordwall 2014-01-08 14:14:48 +01:00
parent bfbee94fec
commit 2e5193347e
19 changed files with 342 additions and 99 deletions
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28
akka-docs/rst/java/cluster-usage.rst
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@ -44,12 +44,12 @@ An actor that uses the cluster extension may look like this:
.. literalinclude:: ../../../akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/simple/SimpleClusterListener.java
:language: java
The actor registers itself as subscriber of certain cluster events. It gets notified with a snapshot event, ``CurrentClusterState``
that holds full state information of the cluster. After that it receives events for changes that happen in the cluster.
The actor registers itself as subscriber of certain cluster events. It receives events corresponding to the current state
of the cluster when the subscription starts and then it receives events for changes that happen in the cluster.
The easiest way to run this example yourself is to download `Typesafe Activator <http://typesafe.com/platform/getstarted>`_
and open the tutorial named `Akka Cluster Samples with Java <http://typesafe.com/activator/template/akka-sample-cluster-java>`_.
It contains instructions of how to run the <code>SimpleClusterApp</code>.
It contains instructions of how to run the ``SimpleClusterApp``.
Joining to Seed Nodes
^^^^^^^^^^^^^^^^^^^^^
@ -166,15 +166,27 @@ Subscribe to Cluster Events
^^^^^^^^^^^^^^^^^^^^^^^^^^^
You can subscribe to change notifications of the cluster membership by using
``Cluster.get(system).subscribe(subscriber, to)``. A snapshot of the full state,
``akka.cluster.ClusterEvent.CurrentClusterState``, is sent to the subscriber
as the first event, followed by events for incremental updates.
``Cluster.get(system).subscribe``.
.. includecode:: ../../../akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/simple/SimpleClusterListener2.java#subscribe
A snapshot of the full state, ``akka.cluster.ClusterEvent.CurrentClusterState``, is sent to the subscriber
as the first message, followed by events for incremental updates.
Note that you may receive an empty ``CurrentClusterState``, containing no members,
if you start the subscription before the initial join procedure has completed.
This is expected behavior. When the node has been accepted in the cluster you will
receive ``MemberUp`` for that node, and other nodes.
If you find it inconvenient to handle the ``CurrentClusterState`` you can use
``ClusterEvent.initialStateAsEvents()`` as parameter to ``subscribe``.
That means that instead of receiving ``CurrentClusterState`` as the first message you will receive
the events corresponding to the current state to mimic what you would have seen if you were
listening to the events when they occurred in the past. Note that those initial events only correspond
to the current state and it is not the full history of all changes that actually has occurred in the cluster.
.. includecode:: ../../../akka-samples/akka-sample-cluster-java/src/main/java/sample/cluster/simple/SimpleClusterListener.java#subscribe
The events to track the life-cycle of members are:
* ``ClusterEvent.MemberUp`` - A new member has joined the cluster and its status has been changed to ``Up``.
@ -190,6 +202,10 @@ There are more types of change events, consult the API documentation
of classes that extends ``akka.cluster.ClusterEvent.ClusterDomainEvent``
for details about the events.
Instead of subscribing to cluster events it can sometimes be convenient to only get the full membership state with
``Cluster.get(system).state()``. Note that this state is not necessarily in sync with the events published to a
cluster subscription.
Worker Dial-in Example
----------------------