[aidos]

Clever. I like that (using the closure).

I've never used Elixir but toyed with Erlang many years ago - is it called asynchronously by the logging process in Elixir? If so, I guess you're relying on immutable data structures to make sure you get the correct logging output?

[derefr]

Everything goes through an async message send to a gen_event (error_logger). The gen_event itself can have annoyingly synchronous+serial behavior with respect to its backends, but gen_event handlers aren't supposed to do much heavy-lifting; they mostly just decide whether they want a message, and then forward it to some backend process to do the formatting+writing+etc.

This gives you another neat benefit, nearly for free: if you have, say, application Foo on node A, wanting to log to SyslogSink on node B, then Foo first sends its logs to a gen_event on A, and the SyslogSink handler in that gen_event gets the opportunity to drop messages, using whatever logic SyslogSink likes, before forwarding them over to B (which might be half-way across the Internet.)