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| | '''Revised on:''' {{REVISIONMONTH1}}/{{REVISIONDAY}}/{{REVISIONYEAR}} by {{REVISIONUSER}} | | '''Revised on:''' {{REVISIONMONTH1}}/{{REVISIONDAY}}/{{REVISIONYEAR}} by {{REVISIONUSER}} |
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| − | == Overview ==
| + | The page was moved to developers documentation: http://docs.openstack.org/developer/taskflow/inputs_and_outputs.html |
| − | | |
| − | In taskflow there are multiple ways to design how your tasks/flows and engines get inputs and produce outputs. This document will help you understand what those ways are and how to use those ways to accomplish your desired taskflow usage pattern as well as include examples that show common ways of providing input and getting output.
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| − | | |
| − | === Task & Flow Inputs and Outputs ===
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| − | | |
| − | '''See:''' [[TaskFlow/Task_Arguments_and_Results|Task & Flow Arguments and Results]]
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| − | | |
| − | === Engine Inputs and Outputs ===
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| − | | |
| − | ==== Storage ====
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| − | | |
| − | The storage layer is how an engine persists flow and task details. | |
| − | | |
| − | For more in-depth design details: [[TaskFlow/Persistence|persistence]].
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| − | | |
| − | ===== Inputs =====
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| − | | |
| − | '''The problem:''' how to prepopulate your engine with arguments (so that dependent tasks can immediately start running).
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| − |
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| − | >>> from taskflow import task
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| − | >>> from taskflow import engines
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| − | >>> from taskflow.patterns import linear_flow as lf
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| − | >>>
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| − | >>> class CatTalk(task.Task):
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| − | ... def execute(self, meow):
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| − | ... print meow
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| − | ... return "cat"
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| − | ...
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| − | >>> class DogTalk(task.Task):
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| − | ... def execute(self, woof):
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| − | ... print woof
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| − | ... return "dog"
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| − | ...
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| − | >>> flo = lf.Flow("cat-dog")
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| − | >>> flo.add(CatTalk(), DogTalk(provides="dog"))
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| − | >>> engines.run(flo)
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| − | Traceback (most recent call last):
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| − | File "<stdin>", line 1, in <module>
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| − | File "/usr/lib/python2.6/site-packages/taskflow/engines/helpers.py", line 110, in run
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| − | engine.run()
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| − | File "/usr/lib/python2.6/site-packages/taskflow/utils/lock_utils.py", line 51, in wrapper
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| − | return f(*args, **kwargs)
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| − | File "/usr/lib/python2.6/site-packages/taskflow/engines/action_engine/engine.py", line 104, in run
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| − | raise exc.MissingDependencies(self._flow, sorted(missing))
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| − | taskflow.exceptions.MissingDependencies: taskflow.patterns.linear_flow.Flow: cat-dog;
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| − | 2 requires ['meow', 'woof'] but no other entity produces said requirements
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| − | | |
| − | '''To solve this you would want to do the following to make your flow run smoothly:'''
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| − | | |
| − | >>> from taskflow import task
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| − | >>> from taskflow import engines
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| − | >>> from taskflow.patterns import linear_flow as lf
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| − | >>>
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| − | >>> class CatTalk(task.Task):
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| − | ... def execute(self, meow):
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| − | ... print meow
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| − | ... return "cat"
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| − | ...
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| − | >>> class DogTalk(task.Task):
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| − | ... def execute(self, woof):
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| − | ... print woof
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| − | ... return "dog"
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| − | ...
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| − | >>> flo = lf.Flow("cat-dog")
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| − | >>> flo.add(CatTalk(), DogTalk(provides="dog"))
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| − | >>> engines.run(flo, store={'meow': 'meow', 'woof': 'woof'})
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| − | meow
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| − | woof
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| − | {'meow': 'meow', 'woof': 'woof', 'dog': 'dog'}
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| − | | |
| − | '''Note:''' you can also directly interact with the engine storage layer to add additional values although you must use the <code>load</code> method instead.
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| − | | |
| − | >>> flo = lf.Flow("cat-dog")
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| − | >>> flo.add(CatTalk(), DogTalk(provides="dog"))
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| − | >>> eng = engines.load(flo, store={'meow': 'meow'})
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| − | >>> eng.storage.inject({"woof": "bark"})
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| − | >>> eng.run()
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| − | meow
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| − | bark
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| − | | |
| − | ===== Outputs =====
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| − | | |
| − | '''Note:''' as you can see the result of the previous <code>run</code> method is the results of all tasks that have ran.
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| − | | |
| − | '''This same data can be fetched in a more precise manner by doing the following:'''
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| − | | |
| − | >>> eng = engines.load(flo, store={'meow': 'meow', 'woof': 'woof'})
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| − | >>> eng.run()
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| − | meow
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| − | woof
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| − | >>> print(eng.storage.fetch_all())
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| − | {'meow': 'meow', 'woof': 'woof', 'dog': 'dog'}
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| − | >>> print(eng.storage.fetch("dog"))
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| − | dog
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| − | | |
| − | ==== Notifications ====
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| − | | |
| − | '''What:''' engines provide a way to receive notification on task and flow state transitions.
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| − | | |
| − | '''Why:''' state transition notifications are useful for monitoring, logging, metrics, debugging, affecting further engine state (and other unknown ''future'' usage).
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| − | | |
| − | ===== Task notifications =====
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| − | | |
| − | A basic example is the following:
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| − | | |
| − | >>> from taskflow import task
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| − | >>> from taskflow import engines
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| − | >>> from taskflow.patterns import linear_flow as lf
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| − | >>>
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| − | >>> class CatTalk(task.Task):
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| − | ... def execute(self, meow):
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| − | ... print(meow)
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| − | ... return "cat"
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| − | ...
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| − | >>> class DogTalk(task.Task):
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| − | ... def execute(self, woof):
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| − | ... print(woof)
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| − | ... return 'dog'
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| − | ...
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| − | >>> def task_transition(state, details):
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| − | ... print("Task %s transition to state %s" % (state, details['task_name']))
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| − | ...
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| − | >>> flo = lf.Flow("cat-dog")
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| − | >>> flo.add(CatTalk(), DogTalk(provides="dog"))
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| − | <taskflow.patterns.linear_flow.Flow object at 0x2263510>
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| − | >>> eng = engines.load(flo, store={'meow': 'meow', 'woof': 'woof'})
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| − | >>> eng.task_notifier.register("*", task_transition)
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| − | >>> eng.run()
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| − | Task RUNNING transition to state __main__.CatTalk
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| − | meow
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| − | Task SUCCESS transition to state __main__.CatTalk
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| − | Task RUNNING transition to state __main__.DogTalk
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| − | woof
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| − | Task SUCCESS transition to state __main__.DogTalk
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