TP2000-1685 Fix packaging, envelope queue regression whilst guarding against race conditions

[dalecannon]

TP2000-1685 Fix packaging, envelope queue regression whilst guarding against race conditions

Why

The setting of a packaged workbasket's processing_started_at field wasn't taking effect.

Inside PackagedWorkBasket.begin_processing(), the variable instance was used to set timestamp value of the packaged workbasket being processed. However, the function's decorator, @save_after, relied on a different reference, self, which lacked the new timestamp value. When the decorator called self.save(), the processing timestamp of the packaged workbasket would remain as its default value of null.

What

• Reinstates the reverted PR TP2000-1577 Correct usage of select_for_update() in packaged workbasket instance methods #1358

• Checks that the processing timestamp is not null following a transition from awaiting processing to currently processing in test_success_processing_transition unit test

• Sets the processing timestamp value on self instead of instance in PackagedWorkBasket.begin_processing(), ensuring the most up-to-date reference of the packaged workbasket instance propagates through function decorators. (Note that other queue management function use @refresh_after decorator instead).

• Adds an additional test case to TestPackagingQueueRaceConditions

• Ensures lingering thread-local DB connections inside TestPackagingQueueRaceConditions are closed to avoid warnings/errors about test DB teardown and creation