Parallel requests and Exception handling

[z0isch]

The program below logs the error when using 4.0.0, but when I upgrade to 5.0.0 it no longer logs the error

module Main where

import Prelude

import Control.Monad.Aff (Aff, launchAff)
import Control.Monad.Aff.Console (log, logShow)
import Control.Monad.Eff.Exception (EXCEPTION, error)
import Control.Monad.Error.Class (throwError, try)
import Control.Parallel (parallel, sequential)
import Data.Tuple (Tuple(..))
import Network.HTTP.Affjax (AJAX, get)

getPostbin :: forall eff.  Aff (exception :: EXCEPTION, ajax :: AJAX | eff) String
getPostbin = do
  resp <- get "http://postb.in/BgIt83CL"
  void $ throwError (error "Oops")
  pure resp.response

main = void $ launchAff do
    t <- try $ sequential $ Tuple <$> parallel getPostbin <*> parallel getPostbin
    logShow t

[garyb]

Is it the "Oops" error you're expecting to see? This is down to a change in Aff rather than affjax, and I think it may be intentional. /cc @natefaubion

[z0isch]

Yeah, I'd like to catch the oops error. If I just do a delay instead of the get I can catch the error, so that's why I kinda assumed it would be an issue with affjax.

[garyb]

Hmm maybe you're right then! I just took a look at the diff between v4 and v5, and although it's "just" the aff update it wasn't entirely straight forward.

[safareli]

can you see the error if you do main = runAff_ log do ...?

[z0isch]

Unfortunately it's still not showing with that change

[natefaubion]

This is probably #112. When running things in parallel, if one throws an exception the runtime will cancel the other fibers. However cancellation is broken, and so the canceller never yields, hanging it.

[garyb]

@natefaubion as per #117 (comment), with a fixed canceller this is still broken, but definitely seems to be in Aff now:

purescript-affjax\output\Effect.Aff\foreign.js:83
        throw error;
        ^

TypeError: Cannot read property 'constructor' of null
    at Object.isLeft (purescript-affjax\output\Effect.Aff\index.js:76:112)
    at join (purescript-affjax\output\Effect.Aff\foreign.js:720:16)
    at purescript-affjax\output\Effect.Aff\foreign.js:778:19
    at purescript-affjax\output\Effect.Aff\foreign.js:669:29
    at runEff (purescript-affjax\output\Effect.Aff\foreign.js:80:7)
    at run (purescript-affjax\output\Effect.Aff\foreign.js:496:15)
    at purescript-affjax\output\Effect.Aff\foreign.js:333:19
    at drain (purescript-affjax\output\Effect.Aff\foreign.js:120:9)
    at Object.enqueue (purescript-affjax\output\Effect.Aff\foreign.js:141:11)
    at purescript-affjax\output\Effect.Aff\foreign.js:330:27

Should we open an issue there?