[Haskell-cafe] Re: Asynchronous exception wormholes kill modularity

On 07/04/10 21:23, Bas van Dijk wrote:

On Wed, Apr 7, 2010 at 5:12 PM, Simon Marlow wrote:

...

Comments?

I really like this design.

One question, are you planning to write the MVar utility functions using 'mask' or using 'nonInterruptibleMask'? As in:

...

withMVar :: MVar a -> (a -> IO b) -> IO b withMVar m f = whichMask? $ \restore -> do a<- takeMVar m b<- restore (f a) `onException` putMVar m a putMVar m a return b

Definitely the ordinary interruptible mask. It is the intention that the new nonInterruptibleMask is only used in exceptional circumstances where dealing with asynchronous exceptions emerging from blocking operations would be impossible to deal with. The more unwieldy name was chosen deliberately for this reason. The danger with nonInterruptibleMask is that it is all too easy to write a program that will be unresponsive to Ctrl-C, for example. It should be used with great care - for example when there is reason to believe that any blocking operations that would otherwise be interruptible will only block for short bounded periods. In the case of withMVar, if the caller is concerned about the interruptibility then they can call it within nonInterruptibleMask, which overrides the interruptible mask in withMVar. Cheers, Simon