Use CDL to block threads to avoid flaky tests.

[aoli-al]

Description

This PR fixes a flaky test in testIntraMergeThreadPoolIsLimitedByMaxThreads. The test uses sleep to block thread execution which is not deterministic due to concurrency issues. This PR replaces the sleep statement with a CountDownLatch.

[benwtrent]

Hey! Getting rid of Thread.sleep! nice.

I ran the test many thousands of times off of main and here, with various amounts of thread switching due to running stress-ng in a different terminal (thus exercising my CPU threads and kicking the process off).

It never failed, but getting rid of sleep is justification enough IMO. I will merge and backport.

Maybe add an entry in CHANGES for the next 10.x release under the

Other
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tag?

[aoli-al]

Thanks! I've updated the CHANGES.txt file.

BTW, we are building a concurrency testing framework (Fray) that allows developers to test concurrent programs deterministically under different thread interleavings. I tested this fix with Fray for 10 minus, and Fray did not find any bugs.

In addition to this bug, Fray has found several concurrency bugs, including #13593, #13571, #13552, and #13547. Feel free to try it and send us your feedback. We are trying to make it more developer-friendly these days.

[benwtrent]

Very useful @aoli-al thank you!

[dweiss]

BTW, we are building a concurrency testing framework (Fray) that allows developers to test concurrent programs deterministically under different thread interleavings

That's very interesting. Is there any writeup (other than the code) that explains how you're doing this?

[aoli-al]

@dweiss Yes, we have a paper on Fray https://aoli.al/papers/fray-arxiv.pdf. I'm also working on blogs to discuss Fray in more detail. I'll let you know as soon as they are ready.