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