Github user zsxwing commented on the pull request:
https://github.com/apache/spark/pull/6852#issuecomment-112722654
> There are certainly some memory barriers in between the writes and reads
without this.
For these tests, there is no memory barrier because the checking codes are
called after `ssc.start()` immediately.
And one potential issue is that, e.g., writing and reading a
java.util.HashMap at the same time may cause an infinite loop:
http://bugs.java.com/bugdatabase/view_bug.do?bug_id=6423457
> If a HashMap is used in a concurrent setting with insufficient
synchronization,
it is possible for the data structure to get corrupted in such a way that
infinite loops appear in the data structure and thus get() could loop
forever.
Of cause, I'm not sure if scala.collection.mutable.HashMap has a similar
issue.
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