[Haskell-cafe] Space leak with recursion

[Tom Ellis]

On Thu, Apr 23, 2015 at 07:27:08PM +0200, Martijn Rijkeboer wrote:
> pollSockets :: State -> IO ()
> pollSockets state =
>     void $ poll (-1)
>        [ Sock (listenSocket state) [In] (Just $ observerHandleEvts state)
>        , Sock (snapSocket state)   [In] (Just $ snapshotHandleEvts state)
>        ]
> 
> 
> observerHandleEvts :: State -> [Event] -> IO ()
> observerHandleEvts state _ = do
>     void $ receiveMulti $ listenSocket state
>     pollSockets state
> 
> 
> snapshotHandleEvts :: State -> [Event] -> IO ()
> snapshotHandleEvts state _ = do
>     void $ receiveMulti $ snapSocket state
>     pollSockets state

What happens here if there is an event waiting on both the listen socket
*and* the snap socket?  It looks like `observerHandleEvts` will be called
and, since it recursively calles `pollSockets`, the `snapshotHandleEvts`
handler will not be run, although its continuation will be kept around
leaking space.

It seems unwise to make a recursive call to the event loop inside a handler.

Tom