Akka/Scala example source code file (fault-tolerance-sample.rst)

This example Akka source code file (fault-tolerance-sample.rst) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Akka and Scala source code examples by using tags.

All credit for the original source code belongs to akka.io; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Akka tags/keywords

counter, counterservice, description, sample, step, storage, storageexception, the, when, worker

The fault-tolerance-sample.rst Akka example source code

.. _fault-tolerance-sample-scala:

Diagrams of the Fault Tolerance Sample
----------------------------------------------



.. image:: ../images/faulttolerancesample-normal-flow.png

*The above diagram illustrates the normal message flow.*

**Normal flow:**

======= ==================================================================================
Step    Description
======= ==================================================================================
1       The progress ``Listener`` starts the work.
2       The ``Worker`` schedules work by sending ``Do`` messages periodically to itself
3, 4, 5 When receiving ``Do`` the ``Worker`` tells the ``CounterService``
        to increment the counter, three times. The ``Increment`` message is forwarded
        to the ``Counter``, which updates its counter variable and sends current value
        to the ``Storage``.
6, 7    The ``Worker`` asks the ``CounterService`` of current value of the counter and pipes
        the result back to the ``Listener``.
======= ==================================================================================


.. image:: ../images/faulttolerancesample-failure-flow.png

*The above diagram illustrates what happens in case of storage failure.*

**Failure flow:**

=========== ==================================================================================
Step        Description
=========== ==================================================================================
1           The ``Storage`` throws ``StorageException``.
2           The ``CounterService`` is supervisor of the ``Storage`` and restarts the
            ``Storage`` when ``StorageException`` is thrown.
3, 4, 5, 6  The ``Storage`` continues to fail and is restarted.
7           After 3 failures and restarts within 5 seconds the ``Storage`` is stopped by its
            supervisor, i.e. the ``CounterService``.
8           The ``CounterService`` is also watching the ``Storage`` for termination and
            receives the ``Terminated`` message when the ``Storage`` has been stopped ...
9, 10, 11   and tells the ``Counter`` that there is no ``Storage``.
12          The ``CounterService`` schedules a ``Reconnect`` message to itself.
13, 14      When it receives the ``Reconnect`` message it creates a new ``Storage`` ...
15, 16      and tells the ``Counter`` to use the new ``Storage``
=========== ==================================================================================

Full Source Code of the Fault Tolerance Sample
------------------------------------------------------

.. includecode:: code/docs/actor/FaultHandlingDocSample.scala#all