GitHub user andrewor14 opened a pull request:
https://github.com/apache/spark/pull/544
[SPARK-1615] Synchronize accesses to the LiveListenerBus' event queue
Much of SparkListenerSuite relies on LiveListenerBus's `waitUntilEmpty()`
method. As the name suggests, this waits until the event queue is empty.
However, the following race condition could happen:
(1) We dequeue an event
(2) The queue is empty, we return true (even though the event has not been
processed)
(3) The test asserts something assuming that all listeners have finished
executing (and fails)
(4) The listeners receive and process the event
This has been a possible race condition for a long time, but for some
reason we've never run into it.
This PR makes (1) and (4) atomic by synchronizing around it. To do that,
however, we must avoid using `eventQueue.take`, which is blocking and will
cause a deadlock if we synchronize around it. As a workaround, we use the
non-blocking `eventQueue.poll` + a semaphore to provide the same semantics.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/andrewor14/spark stage-info-test-fix
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/544.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #544
----
commit eb486ae4c1d95682c0ebeb62edb242109210312e
Author: Andrew Or <[email protected]>
Date: 2014-04-25T00:21:51Z
Synchronize accesses to the LiveListenerBus' event queue
This guards against the race condition in which we (1) dequeue an event,
and (2) check for queue emptiness before (3) actually processing the
event in all attached listeners.
The solution is to make steps (1) and (3) atomic relatively to (2).
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