On 04/07/10 17:50, Simon Marlow wrote:
On 07/04/10 21:23, Bas van Dijk wrote:
On Wed, Apr 7, 2010 at 5:12 PM, Simon Marlow<marlo...@gmail.com> 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.
it could be called unsafeNonInterruptibleMask
(unsafeUninterruptibleMask?)... after all, 'mask' is uninterruptible for
most/many operations, that's its point, but if we put 'mask' and
'nonInterruptibleMask' next to each other, I think people are likely to
be confused (..less so if there's good Haddock documentation. But i'm
fearing the 'forkOS' debacle where people still wrongly recommend that
because the name sounds good...)
I still would like to see examples of where it's needed, because I
slightly suspect that wrapping possibly-blocking operations in an
exception handler that does something appropriate, along with ordinary
'mask', might be sufficient... But I expect to be proved wrong; I just
haven't figured out how to prove myself wrong.
-Isaac
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