Re: [Haskell] Wait for *either* MVar to be set
Peter Verswyvelen wrote:
... by spawning and killing two threads (which might be an expensive operation, I'm not sure)
pretty cheap in GHC -- they're not system threads
Am I wrong in this? If so, is this something that might be considered as a future enhancement in the GHC libraries and runtime?
Also, look at STM (e.g. TVars), which is designed to do what you want more directly, I think. (timeouts might still use the GHC-thread thing. Don't worry about its performance unless you're measurably suffering from it...) -Isaac
In fact:
import Control.Concurrent.STM import Control.Concurrent.STM.TMVar
-- gets a value from one of a list of TMVars takeTMVars :: [TMVar a] -> STM (TMVar a, a) takeTMVars = foldr fetch retry where fetch v act = (takeTMVar v >>= \a -> return (v, a)) `orElse` act
-- puts the given value into exactly one of a list of TMVars putTMVars :: [TMVar a] -> a -> STM (TMVar a) putTMVars vs a = foldr put retry vs where put v act = (putTMVar v a >> return v) `orElse` act
-- ryan
On Wed, Nov 26, 2008 at 11:41 AM, Isaac Dupree
Peter Verswyvelen wrote:
... by spawning and killing two threads (which might be an expensive operation, I'm not sure)
pretty cheap in GHC -- they're not system threads
Am I wrong in this? If so, is this something that might be considered as a future enhancement in the GHC libraries and runtime?
Also, look at STM (e.g. TVars), which is designed to do what you want more directly, I think.
(timeouts might still use the GHC-thread thing. Don't worry about its performance unless you're measurably suffering from it...)
-Isaac _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
On Wed, 2008-11-26 at 13:25 -0800, Ryan Ingram wrote:
In fact:
import Control.Concurrent.STM import Control.Concurrent.STM.TMVar
-- gets a value from one of a list of TMVars takeTMVars :: [TMVar a] -> STM (TMVar a, a) takeTMVars = foldr fetch retry where fetch v act = (takeTMVar v >>= \a -> return (v, a)) `orElse` act
-- puts the given value into exactly one of a list of TMVars putTMVars :: [TMVar a] -> a -> STM (TMVar a) putTMVars vs a = foldr put retry vs where put v act = (putTMVar v a >> return v) `orElse` act
Of course those are TMVars, using STM. So in STM it is easy, whereas with MVars it is a bit harder. Duncan
participants (3)
-
Duncan Coutts -
Isaac Dupree -
Ryan Ingram