akamaus:
Donald Bruce Stewart wrote:
Maybe your loop does no allocations, so the scheduler can't get in and do a context switch. You could put the computation in an external program, and run it over a fork, using unix signals in the external program to kill the computation after a period of time.
I thought about doing that, but function is closely connected with the rest of the program. Running it in another process would require some parsing of its arguments and I want circumvent these difficulties.
Ah, I've found another example. This function attempts to run an expensive computation. If it doesn't return within a given time, a cheap function is used instead. This was mostly written by Stefan Wehr: watchdogIO :: Int -- milliseconds -> IO a -- expensive computation -> IO a -- cheap computation -> IO a watchdogIO millis expensive cheap = do mvar <- newEmptyMVar tid1 <- forkIO $ do x <- expensive x `seq` putMVar mvar (Just x) tid2 <- forkIO $ do threadDelay (millis * 1000) putMVar mvar Nothing res <- takeMVar mvar case res of Just x -> do info ("EXPENSIVE was used") killThread tid2 `catch` (\e -> warn (show e)) return x Nothing -> do info ("WATCHDOG after " ++ show millis ++ " milliseconds") killThread tid1 `catch` (\e -> warn (show e)) cheap -- Don