How to implement Haskell equivalent of invokeAll

Question

I'm looking for equivalent functionality to ExecutorService.invokeAll in Haskell. Do I need to implement it? From documentation:

Executes the given tasks, returning a list of Futures holding their status and results when all complete.

In my use case, tasks spend most of their time waiting on IO, so I only need to avoid constantly blocking main thread which would build up a collection of Either results or errors.

Answer 1

The standard solution to that category of problems is the "async" library. As much as I understand your problem you need something like this:

import Control.Concurrent.Async

processActions :: [IO a] -> IO ()
processActions actions = do
  -- Execute all the actions concurrently and
  -- get a list of asyncs (an equivalent to futures):
  asyncs <- mapM async actions
  -- Do whatever you want...
  -- ...
  -- Block until all the asyncs complete:
  mapM_ wait asyncs

However the library provides a lot of other patterns, so you should just check it out. There's a possibility that what you need is the mapConcurrently function.

Answer 2

No problems. Just use the async library and run mapM async someListOfJobs to get a list of Asyncs on which you can wait, poll, and many other operations.