In the event manager's registerFd_, we find:
registerFd_ :: EventManager -> IOCallback -> Fd -> Event -> Lifetime
-> IO (FdKey, Bool)
registerFd_ mgr@(EventManager{..}) cb !fd !evs lt = do
... <- ...
(modify,ok) <- withMVar (callbackTableVar mgr fd) $ \tbl -> do
... <- ...
-- this simulates behavior of old IO manager:
-- i.e. just call the callback if the registration fails.
when (not ok) (cb reg evs)
return (reg,modify)
A comment and a question. Comment: registerFd_ is only ever called in
contexts where exceptions are masked, so withMVar is doing some needless
mask/restore. Question: why do we immidiately call the callback if event
registration fails? This means that if event registration fails during
something like `threadWaitRead`, the end result would be that
`threadWaitRead` would just return immidiately. That doesn't seem good.
--
-Andrew Thaddeus Martin
