moved ThreadedMonad to Types

1 files changed, 38 insertions, 0 deletions

diff --git a/Assistant/Types/ThreadedMonad.hs b/Assistant/Types/ThreadedMonad.hs
new file mode 100644
index 000000000..1a2aa7eb7
--- /dev/null
+++ b/Assistant/Types/ThreadedMonad.hs
@@ -0,0 +1,38 @@
+{- making the Annex monad available across threads
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Types.ThreadedMonad where
+
+import Common.Annex
+import qualified Annex
+
+import Control.Concurrent
+import Data.Tuple
+
+{- The Annex state is stored in a MVar, so that threaded actions can access
+ - it. -}
+type ThreadState = MVar Annex.AnnexState
+
+{- Stores the Annex state in a MVar.
+ -
+ - Once the action is finished, retrieves the state from the MVar.
+ -}
+withThreadState :: (ThreadState -> Annex a) -> Annex a
+withThreadState a = do
+	state <- Annex.getState id
+	mvar <- liftIO $ newMVar state
+	r <- a mvar
+	newstate <- liftIO $ takeMVar mvar
+	Annex.changeState (const newstate)
+	return r
+
+{- Runs an Annex action, using the state from the MVar. 
+ -
+ - This serializes calls by threads; only one thread can run in Annex at a
+ - time. -}
+runThreadState :: ThreadState -> Annex a -> IO a
+runThreadState mvar a = modifyMVar mvar $ \state -> swap <$> Annex.run state a