[Haskell-cafe] Help with async library and killing child processes
mikehulluk at gmail.com
Tue Mar 17 20:50:42 UTC 2020
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
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
Nothing -> do
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 ->
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,
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