Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/15618#discussion_r85663898
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/scheduler/ReceiverTracker.scala
---
@@ -154,6 +147,17 @@ class ReceiverTracker(ssc: StreamingContext,
skipReceiverLaunch: Boolean = false
throw new SparkException("ReceiverTracker already started")
}
+ if (receivedBlockTracker == null) {
--- End diff --
It looks like this is meant to be restartable, in that it will allow a
stopped tracker to call `start()` again. If that's the case, then
`receivedBlockTracker` needs to be nulled in `stop()`, and then this check
isn't needed I think because it should really be null. In fact if you like you
can require that it's null, and that endpoint is null, in `start()`?
But then ... I think this method needs to throw an exception also if
`isTrackerStopping` at the start. It won't observe the intermediate state
because of syncrhonization, but it could be left in this state if stopping
failed.
I am wary of going too far down a path of fixing or changing the corner
cases here. I do agree that there's a legitimate mismatch between where the
tracker is initialized and stopped, and I think the changes you made and that
possibly the ones I mention here together improve the situation without
complicating it further.
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