[SPARK-6860][Streaming][WebUI] Fix the possible inconsistency of StreamingPage

[zsxwing]

Because StreamingPage.render doesn't hold the listener lock when generating the content, the different parts of content may have some inconsistent values if listener updates its status at the same time. And it will confuse people.

This PR added listener.synchronized to make sure we have a consistent view of StreamingJobProgressListener when creating the content.

[srowen]

That makes some sense. It depends on the methods that mutate the listener also being synchronized on the object. It looks like they are, at a glance, but have you looked into that a bit?

[SparkQA]

Test build #30076 has finished for PR 5470 at commit 7182498.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.
• This patch does not change any dependencies.

[zsxwing]

That makes some sense. It depends on the methods that mutate the listener also being synchronized on the object. It looks like they are, at a glance, but have you looked into that a bit?

Thank you for reminding me. Some public methods of StreamingJobProgressListener are not protected by synchronized. I will update them, too.

[SparkQA]

Test build #30081 has finished for PR 5470 at commit cec6f92.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.
• This patch does not change any dependencies.

[srowen]

LGTM. The first commit fixes a problem that would indeed in rare cases cause the page to display an inconsistent view of the state, which is probably minor but still bad. The second synchronizes access to mutable data structures that were inconsistently synchronized.

[zsxwing]

@srowen, do you think if this one should be merged to branch 1.3?

[srowen]

I would back-port if anyone felt strongly about it; it seems like a theoretical and cosmetic problem, so didn't seem high priority.

[zsxwing]

I would back-port if anyone felt strongly about it; it seems like a theoretical and cosmetic problem, so didn't seem high priority.

Fair. If necessary, I would help send a back-port pull request.

[srowen]

Meh, I'll just back port it. It's low risk.