On Tue, Nov 29, 2005 at 12:00:03PM -0000, Simon Marlow wrote:
> threadDelay is IO-only; there's no way to use threadDelay in an STM
> transaction. For example, if you want to wait for a TVar to go from
> Nothing to Just x with a timeout, you could do this:
>
> readOrTimeout :: TVar (Maybe a) -> Int -> STM (Maybe a)
> readOrTimeout t secs = do
> timeout <- registerTimeout secs
> let check_timeout = do
> b <- readTVar timeout
> if b then return Nothing else retry
> check_t = do
> m <- readTVar t
> case m of
> Nothing -> retry
> Just x -> return x
> atomically $ check_timeout `orElse` check_t
Wouldn't it be
readOrTimeout :: TVar (Maybe a) -> Int -> IO (Maybe a)
^^
?
Alternatively, it would be nice to have a new STM primitive:
wailUntil :: ClockTime -> STM ()
so you would wait until some time-point passes, not for a number of
time-units (waiting for a number of time-units wouldn't work because of
retries). I think it could be efficiently implemented, wouldn't it?
Best regards
Tomasz
--
I am searching for a programmer who is good at least in some of
[Haskell, ML, C++, Linux, FreeBSD, math] for work in Warsaw, Poland
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