Very slow / hangs

[freeman42x]

For example open this repository using HIE for Atom or VSCode and then open Build.hs, in both editors the CPU will get maxed out for minutes (I don't know if it ever stops). During this time Atom interface hangs and nothing is being shown on hover in any of them.

[alanz]

The feedback still needs to be optimised, so we can know what is happening, and whether it is still doing anything useful. See #460

[infinisil]

I'm getting this too now, hasn't happened with the HIE version I used previously (I think that was c68ba8d, now using master (d769a30)). I could do a bisection if that's wanted.

It's unbearably slow, hangs for around 3 minutes at 100% CPU. Looking at the system calls (via htop) reveals no calls happening. No subprocesses running either. The logs silent during that time, and my emacs hangs upon typing during that time.

It happens every time HIE gets restarted, there's no caching happening.

[infinisil]

Here are the logs of my ~4 minute hang at the start: https://gist.github.com/d480967ced87f011a6782890fa83dfd9

Ping @bubba

[infinisil]

Apparently the reason for my slowdown was TemplateHaskell. Removing all {-# LANGUAGE TemplateHaskell #-} from the closure of all imported modules of my own makes it go fast again.

[infinisil]

Note that this slowdown only happens exactly once during a HIE run. And it happens whenever it first encounters a module using template haskell. This means I can write a simple

module Main where
main = putStrLn "hi"

then start HIE, everything fine, no slowdown. Then I can add

{#- LANGUAGE TemplateHaskell -#}
module Main where
main = putStrLn "hi"

and the slowdown happens (4 minutes), after that everything works fine again, I can even remove template haskell again and readd it, no slowdown ever again in that HIE session.

I can then restart HIE on that file, and the slowdown happens on startup again, because template haskell is present then.

[infinisil]

With latest master, the problem isn't there (06de34e)

Nope, still there

[infinisil]

Aha! This is due to hie-nix doing static linking by default. I've now switched to my new https://github.com/infinisil/all-hies and will merge infinisil/all-hies#3 soon which fixes it.