What shall happen if the limit is reached?

park until some ongoing applications have finished - this is all promise-based, so concurrent-applications is equivalent to unresolved-promises

i think i'll need a queue of requested applications and some structure of active applications

and i need it on both clj+cljs ... and not sure of the best structures off the top of my head

or if i can pick up a lib and avoid writing the code 😬

sounds a bit like claypoole?

hmm - that's could be worth a look @U0525KG62 - the structures required may be similar (although claypoole is clj only and explicitly threadpool-based, so i can't actually use it)

some sort of token pool might do the same I suppose?

can't work unless you've got the working token?

It'd submit to a fixed worker pool, for java Executors/newFixedThreadPool in js maybe some like https://github.com/josdejong/workerpool

You can wrap it with a semaphore then not have to worry about where the function is running

In clojurescript?

Ah, woops. You can implement a semaphore with channels

giving up on this... i did an implementation, but it wasn't much faster than using a manifold stream with a buffer to control concurrency, and since it's for a streams lib i'm just going to munge streams instead