Close Encounters of The Java Memory Model Kind

Two years ago I painfully researched and built JMM Pragmatics talk and transcript, hoping it would highlight the particular dark corners of the Java Memory Models for those who cannot afford to spend years studying the formalisms, and deriving the actionable insights from them. JMM Pragmatics has helped many people, but there is still lots of confusion about what Memory Model guarantees, and what it does not.

In this post, we will try to follow up on particular misunderstandings about Java Memory Model, hopefully on the practical examples. The examples use the APIs from the jcstress suite, which are concise enough for a reader, and are runnable.


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This is a fairly large piece of writing. In this age of attention-scarce Internet it would normally be presented as a series of posts, one section each. Let’s pretend we did that 🙂 If you run out of time/patience to read through, bookmark, and restart from the section you’ve left at.

Most examples in this post came from public and private discussions we’ve had over the years. I would not claim they cover all memory model abuses. If you have an interesting case that is not covered here, don’t hesitate to drop me a mail, and we can see if it fits the narrative somewhere. concurrency-interest is the mailing list where you can discuss interesting cases in public.