On Oct 27, 2023, at 11:51 AM, Viktor Dukhovni <ietf-dane@dukhovni.org> wrote:

On Fri, Oct 27, 2023 at 07:43:07PM +0100, Tom Ellis wrote:

On Fri, Oct 27, 2023 at 11:36:53AM -0700, David Banas wrote:

What is the simplest way to translate a non-monadic line of Haskell code, such as:

res = map foo xs `using` parList rseq

For use in the IO monad?

This doesn’t work:

res <- mapM fooM xs `using` parTraversable rseq

The docs for Control.Parallel.Strategies say "The parallel tasks
evaluated by a Strategy may have no side effects. For
non-deterministic parallel programming, see Control.Concurrent."[1].
So I guess you should look into Control.Concurrent[2].

For a more friendly interface:

   https://hackage.haskell.org/package/async-2.2.4/docs/Control-Concurrent-Async.html

If the number of concurrent tasks is reasonably modest, a good fit could
be `mapConcurrently`.

For much larger numbers of tasks, it is best to run the jobs at a
bounded concurrency, which may bring a BoundedChan to which the items to
process are written, another to which results are written and a set of
threads that do the processing, repeatedly reading more data until the
channel is drained. 

*The* book on subject is: https://simonmar.github.io/pages/pcph.html

--
   Viktor.
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