`MutexImpl.unlock()` hangs forever when locked through `Semaphore.aquire()` about kotlinx.coroutines HOT 4 OPEN

I'm not sure if this is really a bug

It is, by the substitution principle (https://en.wikipedia.org/wiki/Liskov_substitution_principle)

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However, given that it requires a cast that relies on knowing the implementation details, it's a bug typically invisible to the user, so it's low-priority. When we merge #2045, this will get fixed automatically.

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@lukellmann could you please elaborate on how you've stumbled across this bug?

Mutex implementing Semaphore is a private implementation detail that we cannot hide (or don't want to; it incurs a small footprint hit); I wonder if this is something you use in your codebase: understanding the scenario would help us designing better and more robust primitives

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I read the source and realized that this could happen. I then constructed this code. So it doesn't impact any real code of mine.

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