Hi,I am currently learning Haskell, and really enjoying it, thankyou to the community for this well considered language.
I have started using the async library, and I can't quite figure out some of the documentation, and I wonder if someone could help.
Makes the comment that: "
This is a useful variant of async that ensures an Async is never left running unintentionally." However, I can't see how I would use this.
To make the example more concrete, I have a function that looks like this:
runNodeHwBridgeUdp :: NodeHwInterface -> NodeHwUdpConfig-> IO()
runNodeHwBridgeUdp (NodeHwInterface l0up l0down) config = do
putStrLn "Starting Node bridge"
-- Launch all the subprocesses:
t0 <- async $ (runMsgUpReader hwBridgeSharedData l0up)
t1 <- async $ (evalStateT (runUDPWriter hwBridgeSharedData) (initialUdpDispatchData timeUs) )
t2 <- async $ (runUDPReader hwBridgeSharedData l0down)
putStrLn "Created child processes. Waiting...."
(a, is_exception) <- waitAnyCatchCancel [t0, t1, t2]
case is_exception of
Right _ -> do
error "SHOULD NOT GET HERE"
Left exception -> do
case (fromException exception) of
Just (ex :: HwDestroyException) -> do
putStrLn $ "BRIDGE ENDING: >>>> GOOD: SHUTDOWN: " ++ show exception
Nothing -> do
throwIO exception
return ()
This process launches 3 child processes, and then waits on them. I launch this function as an async-process, and it would be really helpful if when I "cancel"ed it, it would also also cancelled the children, but I don't understand how I would structure that...
t0 <- withAsync $ (runMsgUpReader hwBridgeSharedData l0up) $ \async -> do
????
t1 <- withAsync $ (evalStateT (runUDPWriter hwBridgeSharedData) (initialUdpDispatchData timeUs) ) $ \async -> do
????
t2 <- async $ (runUDPReader hwBridgeSharedData l0down) $ \async -> do
????
I feel like I must be missing something here.
I'd appreciate any input; many thanks for your time,
Mike