[CHY872]

I think this one's weird because the language puts so much effort into making it hard to hit this that you won't notice until it's a gigantic problem. For me, this was enough of a problem that I wrote a Java agent which patches the method which blocks the carrier thread to just throw (ByteBuddy makes it easy!).

Like, it makes sense that when you synchronized on an object, there's room for contention. It seems weird that synchronizing on an _uncontended_ object can cause contention. But that's what this is. The behaviour is that you have target numCores carrier threads, and if someone synchronizes on an object and then does a non-blocking sleep, it's now blocking, because synchronizing upgraded the non-blocking I/O to blocking.

So basically when you hit this issue, it's because not only has the bad thing been happening, it's also been happening badly enough that all the compensation mechanisms have failed.

It's just weird that a whole language level keyword behaves this badly.