Switch AsyncFD to use kEVENT on OSX / *BSD's for Asynchronous thread notification? about nim-chronos HOT 3 OPEN

On my experiments both socketpair and pipe provides same performance and sometimes socketpair is better. The only reason to choose socketpair is that its possible to do read(MSG_PEEK) to check if data is available in socket, there is no way to perform this check on pipe, but it is required for this implementation. Also i know that its not that performant as on Linux/Windows, but at least it is present.
EVFILT_USER was interesting case, but it only supported by FreeBSD and NetBSD, while OpenBSD, DragonflyBSD and MacOS do not support this functionality.

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Sorry, looks like it is present in MacOS but its undocumented.

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On my experiments both socketpair and pipe provides same performance and sometimes socketpair is better. The only reason to choose socketpair is that its possible to do read(MSG_PEEK) to check if data is available in socket, there is no way to perform this check on pipe, but it is required for this implementation.

Nice! Good to know as I wasn't sure how they compared.

EVFILT_USER was interesting case, but it only supported by FreeBSD and NetBSD, while OpenBSD, DragonflyBSD and MacOS do not support this functionality.

Yah I think MacOS and FreeBSD make up a fair bit of the "market share" for development or servers, respectively, for BSD's.

Sorry, looks like it is present in MacOS but its undocumented.

Yah odd it's not in the man page. One stackoverflow thread said it has been available since macos 10.6. Though I suspect Apple wants most developers to use Grand Central Dispatch rather than the raw mechanisms.

Looks like libevent uses it as well. The main thing I noticed with it was a bit of latency improvement.

I might try and make a PR at some point, as I'll be using the asynchronous thread notification and develop on Mac. :)

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