---------------------------
Notifications and listeners
---------------------------

.. testsetup::

    from taskflow import task
    from taskflow.patterns import linear_flow
    from taskflow import engines
    from taskflow.types import notifier
    ANY = notifier.Notifier.ANY

Overview
========

Engines provide a way to receive notification on task and flow state
transitions (see :doc:`states <states>`), which is useful for
monitoring, logging, metrics, debugging and plenty of other tasks.

To receive these notifications you should register a callback with
an instance of the :py:class:`~taskflow.types.notifier.Notifier`
class that is attached to :py:class:`~taskflow.engines.base.Engine`
attributes ``atom_notifier`` and ``notifier``.

TaskFlow also comes with a set of predefined :ref:`listeners <listeners>`, and
provides means to write your own listeners, which can be more convenient than
using raw callbacks.

Receiving notifications with callbacks
======================================

Flow notifications
------------------

To receive notification on flow state changes use the
:py:class:`~taskflow.types.notifier.Notifier` instance available as the
``notifier`` property of an engine.

A basic example is:

.. doctest::

   >>> class CatTalk(task.Task):
   ...   def execute(self, meow):
   ...     print(meow)
   ...     return "cat"
   ...
   >>> class DogTalk(task.Task):
   ...   def execute(self, woof):
   ...     print(woof)
   ...     return 'dog'
   ...
   >>> def flow_transition(state, details):
   ...     print("Flow '%s' transition to state %s" % (details['flow_name'], state))
   ...
   >>>
   >>> flo = linear_flow.Flow("cat-dog").add(
   ...   CatTalk(), DogTalk(provides="dog"))
   >>> eng = engines.load(flo, store={'meow': 'meow', 'woof': 'woof'})
   >>> eng.notifier.register(ANY, flow_transition)
   >>> eng.run()
   Flow 'cat-dog' transition to state RUNNING
   meow
   woof
   Flow 'cat-dog' transition to state SUCCESS

Task notifications
------------------

To receive notification on task state changes use the
:py:class:`~taskflow.types.notifier.Notifier` instance available as the
``atom_notifier`` property of an engine.

A basic example is:

.. doctest::

   >>> class CatTalk(task.Task):
   ...   def execute(self, meow):
   ...     print(meow)
   ...     return "cat"
   ...
   >>> class DogTalk(task.Task):
   ...   def execute(self, woof):
   ...     print(woof)
   ...     return 'dog'
   ...
   >>> def task_transition(state, details):
   ...     print("Task '%s' transition to state %s" % (details['task_name'], state))
   ...
   >>>
   >>> flo = linear_flow.Flow("cat-dog")
   >>> flo.add(CatTalk(), DogTalk(provides="dog"))
   <taskflow.patterns.linear_flow.Flow object at 0x...>
   >>> eng = engines.load(flo, store={'meow': 'meow', 'woof': 'woof'})
   >>> eng.task_notifier.register(ANY, task_transition)
   >>> eng.run()
   Task 'CatTalk' transition to state RUNNING
   meow
   Task 'CatTalk' transition to state SUCCESS
   Task 'DogTalk' transition to state RUNNING
   woof
   Task 'DogTalk' transition to state SUCCESS

.. _listeners:

Listeners
=========

TaskFlow comes with a set of predefined listeners -- helper classes that can be
used to do various actions on flow and/or tasks transitions. You can also
create your own listeners easily, which may be more convenient than using raw
callbacks for some use cases.

For example, this is how you can use
:py:class:`~taskflow.listeners.printing.PrintingListener`:

.. doctest::

   >>> from taskflow.listeners import printing
   >>> class CatTalk(task.Task):
   ...   def execute(self, meow):
   ...     print(meow)
   ...     return "cat"
   ...
   >>> class DogTalk(task.Task):
   ...   def execute(self, woof):
   ...     print(woof)
   ...     return 'dog'
   ...
   >>>
   >>> flo = linear_flow.Flow("cat-dog").add(
   ...   CatTalk(), DogTalk(provides="dog"))
   >>> eng = engines.load(flo, store={'meow': 'meow', 'woof': 'woof'})
   >>> with printing.PrintingListener(eng):
   ...   eng.run()
   ...
   <taskflow.engines.action_engine.engine.SerialActionEngine object at ...> has moved flow 'cat-dog' (...) into state 'RUNNING' from state 'PENDING'
   <taskflow.engines.action_engine.engine.SerialActionEngine object at ...> has moved task 'CatTalk' (...) into state 'RUNNING' from state 'PENDING'
   meow
   <taskflow.engines.action_engine.engine.SerialActionEngine object at ...> has moved task 'CatTalk' (...) into state 'SUCCESS' from state 'RUNNING' with result 'cat' (failure=False)
   <taskflow.engines.action_engine.engine.SerialActionEngine object at ...> has moved task 'DogTalk' (...) into state 'RUNNING' from state 'PENDING'
   woof
   <taskflow.engines.action_engine.engine.SerialActionEngine object at ...> has moved task 'DogTalk' (...) into state 'SUCCESS' from state 'RUNNING' with result 'dog' (failure=False)
   <taskflow.engines.action_engine.engine.SerialActionEngine object at ...> has moved flow 'cat-dog' (...) into state 'SUCCESS' from state 'RUNNING'

Interfaces
==========

.. automodule:: taskflow.listeners.base

Implementations
===============

Printing and logging listeners
------------------------------

.. autoclass:: taskflow.listeners.logging.LoggingListener

.. autoclass:: taskflow.listeners.logging.DynamicLoggingListener

.. autoclass:: taskflow.listeners.printing.PrintingListener

Timing listeners
----------------

.. autoclass:: taskflow.listeners.timing.DurationListener

.. autoclass:: taskflow.listeners.timing.PrintingDurationListener

.. autoclass:: taskflow.listeners.timing.EventTimeListener

Claim listener
--------------

.. autoclass:: taskflow.listeners.claims.CheckingClaimListener

Capturing listener
------------------

.. autoclass:: taskflow.listeners.capturing.CaptureListener

Hierarchy
=========

.. inheritance-diagram::
    taskflow.listeners.base.DumpingListener
    taskflow.listeners.base.Listener
    taskflow.listeners.capturing.CaptureListener
    taskflow.listeners.claims.CheckingClaimListener
    taskflow.listeners.logging.DynamicLoggingListener
    taskflow.listeners.logging.LoggingListener
    taskflow.listeners.printing.PrintingListener
    taskflow.listeners.timing.PrintingDurationListener
    taskflow.listeners.timing.EventTimeListener
    taskflow.listeners.timing.DurationListener
    :parts: 1