Potential memory leak in `drainVar` loop

[natefaubion]

Followup issue mentioned in #8. I've been able to reproduce with only the Eff interface. I changed the take/put loop to force a manual GC every 50000 loops, which keeps it from growing so quickly, but it still grows, and the GC pauses get longer and longer as it has to walk over more and more references. There's definitely an issue here.

/cc @felixSchl

[natefaubion]

I can also confirm that breaking the drainVar loop prevents it from accumulating more memory.

[natefaubion]

@felixsch I think this is actually just console.log buffering, maybe. If I take out the logging on every tick, and instead log every 50,000 ticks, the memory does not balloon.

[natefaubion]

module Test.Loop where

import Prelude

import Control.Monad.Eff (Eff)
import Control.Monad.Eff.AVar (makeEmptyVar, putVar, takeVar)
import Control.Monad.Eff.Console (logShow)
import Data.Either (Either(..))

main :: Eff _ Unit
main = do
  var <- makeEmptyVar
  let
    putLoop n = void $ putVar n var \_ -> do
      when (n < 100000000) do
        putLoop (n + 1)

    takeLoop n = void $ takeVar var case _ of
      Left _ -> pure unit
      Right n' -> do
        if n == 1000
          then do
            logShow n'
            takeLoop 1
          else
            takeLoop (n + 1)

  putLoop 1
  takeLoop 1

This is what I'm using to test. Pushing the takeLoop number down to 1 will cause memory to go up, but something like 1000 will cause it to stay stable, so I can only assume this is not related to avar. If it was avar we should see memory ballooning regardless of what the callbacks do. Let me know if you can reproduce an issue with only avar machinery.