(Rare) deadlock in TestSuite

[edsko]

Very occasionally the test suite seems to deadlock. @dcoutts , perhaps you review the section "Concurrency Control" in TestSuite/TestSuite/State.hs and see if anything jumps out at you?

[dcoutts]

Nothing jumps out at me. What does this deadlock look like? Is it a 0% cpu deadlock or a 100% livelock? A 0% cpu deadlock should be impossible with STM, so if that's the case then it cannot be in those concurrency control functions. If it's livelock then it could plausibly be many transactions retrying and failing. Many of the transactions are read;write on the same var, so if we have loads and loads of threads doing that then we could get lots of reties. Whether that'd be enough to block the progress of e.g. giving up exclusive access I don't know.