Why is it not recommended to do any type of IO in GO-blocks in Clojure? I am doing some IO now: 1. I have 10 users which I want to make an api request (per user) and buffer the result. 2. I create a go-block and a channel per user and put the user on the channel, the go-block will call a 3rd part api. 3. When the api call is done in each go-block I put the result on a "invited" chan which has a go-loop that buffers all messages untill all users are invited, and then continues..

Re io, go blocks are dispatched across a fixed pool of (by default 8) threads. If you block, you tie up a thread and prevent other go blocks from proceeding. In the worst case, you can stop all progress.

It’s better to do this kind of work in a dedicated thread

I see, thank you for the explanation @alexmiller

but it’s a bit hard where to draw the line, right? Would be interested to hear how you do this in practice. I assume logging is fine. What about reading from a datomic db using the peer library?

are <! >! alts alt! the only things that can park and resume from a different thread? Context: we’re introducing a consistent logging context (using pedestal’s log/with-context). Or is that generally a bad idea to mix that and core.async?

outside of a pathological case, logging shouldn't be a significant block to the thread

there's a simple pattern to putting something in a thread and parking on it: (<! (async/thread (f)) will avoid blocking a core.async go thread and uses a separate expandable pool