Proposal: Control.Concurrent.Async

[Sjoerd Visscher]

And perhaps an Alternative instance would also be useful:

instance Alternative Concurrently where
  empty = Concurrently $ forever (threadDelay maxBound)
  Concurrently as <|> Concurrently bs =
    Concurrently $ either id id <$> race as bs

Where "empty" should be the cheapest way to loop forever, I don't know 
if this is the best way to do that. 

Sjoerd

On Wed, 13 Jun 2012 23:58:54 +0200, Sjoerd Visscher 
<sjoerd at w3future.com> wrote:
Hi Simon,
>
> This a really nice and clean library!
>
> I was wondering if it would be useful to have an applicative 
> interface for the concurrently function? Something like this:
>
>   (page1, page2, page3)     <-  runConcurrently $ (,,)     <$> 
> Concurrently (getURL "url1")     <*> Concurrently (getURL "url2")     
> <*> Concurrently (getURL "url3")
>
> More code here: https://gist.github.com/2926572
>
> Thanks,
> Sjoerd
>
> On Jun 8, 2012, at 10:37 AM, Simon Marlow wrote:
>
> > I'd like to add a higher-level concurrency API to the base package. 
> This API has grown while I've been working on examples for my book, 
> and I'm convinced that we should have something like this in the 
> standard libraries.  Here's the API I propose:
> > > 
> http://community.haskell.org/~simonmar/async-stm/Control-Concurrent-Async.html
> > > In fact it already exists in at least two packages on Hackage: 
> 'async' and 'threads'.  My version is a superset of both of these, 
> except for a few small differences (which are up for discussion, of 
> course). 
> > > One good reason to have this package is that it avoids some 
> common pitfalls, such as forgetting to handle exceptions in your 
> child threads.  In the Async API, you get to choose whether to (a) 
> receive the result as 'Either SomeException a', or (b) have the 
> exception re-thrown in the waiting thread.  You don't get to ignore 
> it altogether. 
> > > Another common pitfall avoided by this library is accidentally 
> leaving threads running in the background.  This is handled by 
> withAsync:
> > >  withAsync :: IO a -> (Async a -> IO b) -> IO b
> > > the child thread is always cancelled (i.e. killed) when the 
> second argument returns or throws an exception, if it hasn't finished 
> already. 
> > > > I'm opening this up for discussion so that we can tidy up any 
> inconsistent details and add any functions that people feel are 
> missing.  Naming is obviously up for discussion too. 
> > > Cheers,
> >  Simon
> > > > > _______________________________________________
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> > --
> Sjoerd Visscher
> https://github.com/sjoerdvisscher/blog
>
>
>
>
>
>
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  --
Sjoerd Visscher
http://w3future.com/