Re: Proposal: Control.Concurrent.Async

On 08/06/2012 17:31, Thomas Schilling wrote:

I fixed the docs a tiny bit in: https://github.com/simonmar/async/pull/1

Other comments:

- Module introduction is missing.

Now added.

- There are no tests whatsoever. I would like to have a few stress tests that throw lots of asynchronous exceptions to make sure that exception masking etc behaves correctly.

Also added, including a couple of stress tests. (but the test coverage isn't great, I'll try to improve it in due course)

- Why is there no waitAnyCancel? - Same with waitEitherCancel

Both added. I think that now addresses all the comments that people had. There's one more change I'm thinking about: perhaps instead of wait :: Async a -> IO (Either SomeException a) waitThrow :: Async a -> IO a we should reverse the naming scheme, rename waitThrow to wait and wait to something else (waitCatch?). Rationale: waitThrow seems to be the version we need most often, and it's simpler to use. wait :: Async a -> IO a waitCatch :: Async a -> IO (Either SomeException a) Thoughts? Better names for waitCatch? Latest Haddocks: http://community.haskell.org/~simonmar/async/ Repo: https://github.com/simonmar/async Cheers, Simon

On 8 June 2012 09:37, 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.ht...

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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