Affects Version/s: None
Fix Version/s: 1.0
Existing StreamProcessor implementation doesn't have state variable to represent it's current state(if it's in rebalance/shutdown/running state). Absence of this information leads to following two problems.
- When execution of StreamProcessor.stop() and JobCoordinatorListener.onNewJobModel() happen concurrently, SamzaContainer might be still running after StreamProcessor had been stopped(due to interleaved execution order). Here's a sample execution order:
1. User thread invokes `SamzaContaienr.stop()`.
2. `StreamProcessor.stop()` stops the current running samza container.
3. Before StreamProcessor stops the ZkJobCoordinator, ZkJobCoordinator initializes and executes a new SamzaContainer(Due to change in global processors group).
4. StreamProcessor stops the ZkJobCoordinator.
- When execution of StreamProcessor.stop() and JobCoordinatorListener.jobModelExpired() happen concurrently, StreamProcessor will not be stopped cleanly.
`paused` is state variable held in SamzaContainer to indicate if it has been stopped for new JobModel for JobCoordinator(By default `paused` is set to `false` in `SamzaContainer`). Here's a sample execution order:
1. User thread invokes `SamzaContainer.stop()` and triggers `SamzaContainer.shutdown`. At the point, user thread is waiting for `onContainerStop(paused=false)`(container stopped callback with paused = false).
2. Before the SamzaContainer is shutdown, debounce thread invokes `onJobModelExpired` and triggers `SamzaContainer.pause()`. `SamzaContainer.pause()` sets SamzaContainer local state `paused` to true.
3 . SamzaContainer shuts down and triggers the container shutdown callback: onContainerStop(with paused = true). When paused is set to true in onContainerStop callback, StreamProcessor shutdown sequence is not triggered.
4. StreamProcessor would participate in the processor group coordination activities as if shutdown was not triggered.
5. LocalApplicationRunner.waitForFinish will block indefinitely.
To solve the above problems, following changes were done:
- Add state field to `StreamProcessor` to represent it's current state. Before performing any StreamProcessor operation, it's current state is checked and only if it's valid for the operation then the operation is performed.
- Remove the paused state from SamzaContainer and it is covered by the StreamProcessor state itself.
- Make onJobModelExpired as start state for any custom JobCoordinators.
- Interrupt the container thread on StreamProcessor.stop() if it's running after shutdown timeout.
- Add tests to verify the behavior in StreamProcessor/LocalApplicationRunner.