briqueabraque:
Hi,
After I have spawned a thread with 'forkIO', how can I check if that thread work has finished already? Or wait for it?
The best way to do this is using Control.Exception.finally: (...)
These techniques are needed because forkIO is a very lightweight threading mechanism. Adding precisely the features you need makes for good performance control, as seen in the great computer language shootout benchmarks.
Changing ugly code for bad performance is not that usual in Haskell code :(
I think you misunderstand Chris' remark. He's saying that MVars and forkIO give you bot clean control, and high performance. This code seems quite elegant, for the job you were asking: import Control.Concurrent import Control.Exception main = do done <- run (print (last [1..100000000])) print "Waiting...." takeMVar done print "OK." where run f = do x <- newEmptyMVar forkIO (f `finally` putMVar x ()) return x And the lovely thread-ring benchmark, is also very nice: http://shootout.alioth.debian.org/gp4/benchmark.php?test=threadring&lang=all Where the Haskell code is both the shortest, and fastest. Beautiful code can be very efficient. -- Don