On Dec 28, 2005, at 1:38 PM, Tomasz Zielonka wrote:
On Wed, Dec 28, 2005 at 05:28:28PM +0000, Chris Kuklewicz wrote:
But STM, wrapped in small pieces, makes for interesting IO commands
(untested):
waitForZero :: (Num a, Ord a) => (TVar a) -> IO ()
waitForZero tv = atomically $ do
v <- readTVar tv
when (v>0) retry
This function is rather useless in IO - you will get race conditions.
That's what you get for leaving the STM wonderland ;-)
Actually, I think it works in the particular instance given of
constructing read-write locks because the call to waitForZero is
guarded by a mutex. But it would certainly be easy to introduce a
race condition using constructs like this. Given the alternatives
{use STM fully, use STM some, don't use STM}, I would have a hard
time justifying the "use STM some" alternative (at least for new
programs). If you are OK with introducing a dependency on STM, why
not go whole hog?
Rob Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
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