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The problem with green threads, historically, was that there was no way to do arbitrary syscalls async; if your syscall blocks it blocks all your other green threads. Doh.

io_uring is supposed to be about solving this, but it's quite the kitchen sink so I have no idea how complete it is on the "arbitrary syscall async" front.

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Yes, it's gotten quite large, but I think with far fewer wrong turns in the API compared to the futex. Enough was available async via `epoll()` + having fd interfaces to things that I never was as worried about the arbitrary latency of syscalls, but it's still incredibly cool, especially in the number of calls it avoids outright.

`epoll` doesn’t actually do any IO though, so it doesn’t help with syscall latency. It just avoids the overhead of doing IO via a large number of threads (memory overhead, hard context switches, etc.).

No it doesn't, which is one key reason why I am a fan of `io_uring`. I brought `epoll` up because it does help with the blocking though, for most of the things that matter when it comes to async (at a cost to latency, of course).

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