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Celery Jobs

Celery Jobs are not yet ready for production, because fast-lane/slow-lane work is not complete.

However, all active job types have been migrated to support running under Celery.

Data flow

The database remains the authoritative source of information about a job. Celery is merely a mechanism for running that job. Each attempt to run a job will use its own Celery task.

This may change in the future, because there are many similarities between Celery's Task class and Launchpad's Job class. They could merge, or one could replace the other.

Additional Requirements

Job factory methods should call Job.celeryRunOnCommit(). This schedules the job to run if/when the current transaction is committed. It only affects jobs whose class names are in the jobs.celery.enabled_classes feature flag.

Jobs must provide a 'config' member, which is meant to be a config section, e.g. lp.services.config.config.branchscanner. This member must have a dbuser attribute. The dbuser for each job type should be unique, to aid debugging production problems.

Database job classes such as BranchJob must provide a 'makeDerived' member which returns an IRunnableJob implementation. If there are no derived classes, as with POFileStatsJob, it should simply return itself.

Base classes for specific IRunnableJob classes based on an enum, such as BranchJobDerived, should use EnumeratedSubclass as their metaclass. This will cause each of their subclasses to be registered with the base class when that subclass is declared. EnumeratedSubclass automatically provides the makeSubclass method, which returns an instance of the appropriate subclass for a given database class. This allows makeDerived to be implemented as a one-liner:

    def makeDerived(self):
        return BranchJobDerived.makeSubclass(self)

It is not clear that FooDerived classes are needed, because Storm appears to permit one table to be associated with many classes. Further testing is required.

Job classes should provide a 'context' member which is a database class.

Testing

Jobs should have an integration test to show that they run under Celery correctly.

Here is an example:

class TestViaCelery(TestCaseWithFactory):

    layer = CeleryJobLayer

    def test_DerivedDistroseriesDifferenceJob(self):
        self.useFixture(FeatureFixture({
            FEATURE_FLAG_ENABLE_MODULE: u'on',
            'jobs.celery.enabled_classes': 'DistroSeriesDifferenceJob',
            }))
        dsp = self.factory.makeDistroSeriesParent()
        package = self.factory.makeSourcePackageName()
        with block_on_job():
            job = create_job(dsp.derived_series, package, dsp.parent_series)
            transaction.commit()
        self.assertEqual(JobStatus.COMPLETED, job.status)

The CeleryJobLayer ensures a celeryd is running, to process the job. Configuring the feature flag jobs.celery.enabled_classes='DistroSeriesDifferenceJob' ensures that create_job will request the job to run under celery (as a commit hook). transaction.commit() causes the commit hook to fire, requesting the job to run via celery. lp.services.job.tests.block_on_job waits until the job that was requested to run via celery in its scope has completed.