Re: darcs patch: forkChild, waitForChild, parIO, timeout

8 Nov 2006


      Taral wrote:
...
On 11/7/06, Simon Marlow  wrote:
...
So 'timeout N E' should behave exactly the same as E as long as E 
doesn't time
out.  Three difficulties with this:
1. if E raises an exception, you want the exception propagated to 
the parent.
2. if another thread throws an exception to this thread, E should 
receive the
     exception.
3. E should get the same result from myThreadId.
I think 2 and 3 go together, and require an exception. Here's my try:
data Timeout = Timeout deriving Typeable
timeout n f
   | n < 0 = fmap Just f
   | n == 0 = return Nothing
   | otherwise = do
       pt <- myThreadId
       bracket (forkIO (threadDelay n >> throwDynTo pt Timeout))
               (killThread)
               (fmap Just f) `catchDyn` \Timeout -> return Nothing
Nearly - but this one doesn't nest.  Also, it's possible for the Timeout 
exception to leak.

Cheers,
	Simon