[PATCH] D54889: Fiber support for thread sanitizer

[Dmitry Vyukov via Phabricator via llvm-commits]

dvyukov added a comment.

Lingfeng, thanks for extensive feedback.

> This should allow that logic to work for QEMU at least, and it feels like it should work for all possible other uses (?)

I am not sure there are no programs that use setjmp/longjmp to switch fibers across threads. Yes, man says behavior is undefined. But strictly saying, longjmp shouldn't be used for fiber switching too (it's solely for jumping upwards on the same stack). So I feel people are just relying on implementation details here (let's test it, works, ok, let's use it).

You said that QEMU uses sigsetjmp/siglongjmp for coroutine switches. How does a coroutine always stay on the same thread then? Say, if they have a thread pool servicing all coroutines, I would expect that coroutines are randomly intermixed across threads. So it can happen that we setjmp on one thread, but then reschedule the coroutine with longjmp on another thread.

If it's the case, then it's quite unpleasant b/c it means we need a global list of jmpbufs. And that won't work with the current jmpbug garbage collection logic and sp level checks. So we will probably need to understand that this particular jmpbuf is a fiber and then handle it specially.


Repository:
  rCRT Compiler Runtime

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https://reviews.llvm.org/D54889