Ticket: http://hackage.haskell.org/trac/ghc/ticket/4857 This proposal is to add the following function to Control.Exception: -- | When invoked inside 'mask', this function allows a blocked -- asynchronous exception to be raised, if one exists. It is -- equivalent to performing an interruptible operation (see -- #interruptible#), but does not involve any actual blocking. -- -- When called outside 'mask', or inside 'uninterruptibleMask', this -- function has no effect. allowInterrupt :: IO () allowInterrupt = unsafeUnmask $ return () The above is almost the entire implementation modulo imports, so I didn't bother attaching a patch to the ticket. unsafeUnmask is not exported by Control.Exception, it is an internal function from GHC.IO. Some discussion leading up to this can be found in http://hackage.haskell.org/trac/ghc/ticket/3837. Discussion period: 3 weeks (until 12 Jan 2011) Cheers, Simon