2 files changed, 55 insertions, 14 deletions
diff --git a/Database/Keys/Handle.hs b/Database/Keys/Handle.hs
new file mode 100644
index 000000000..5a5912b0b
--- /dev/null
+++ b/Database/Keys/Handle.hs
@@ -0,0 +1,55 @@
+{- Handle for the Keys database.
+ -
+ - Copyright 2015 Joey Hess <id@joeyh.name>
+ -:
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Database.Keys.Handle (
+	DbHandle,
+	newDbHandle,
+	DbState(..),
+	withDbState,
+	flushDbQueue,
+) where
+
+import qualified Database.Queue as H
+import Utility.Exception
+
+import Control.Concurrent
+import Control.Monad.IO.Class (liftIO, MonadIO)
+
+-- The MVar is always left full except when actions are run
+-- that access the database.
+newtype DbHandle = DbHandle (MVar DbState)
+
+-- The database can be closed or open, but it also may have been
+-- tried to open (for read) and didn't exist yet.
+data DbState = DbClosed | DbOpen H.DbQueue | DbEmpty
+
+newDbHandle :: IO DbHandle
+newDbHandle = DbHandle <$> newMVar DbClosed
+
+-- Runs an action on the state of the handle, which can change its state.
+-- The MVar is empty while the action runs, which blocks other users
+-- of the handle from running.
+withDbState
+	:: (MonadIO m, MonadCatch m)
+	=> DbHandle
+	-> (DbState
+	-> m (v, DbState))
+	-> m v
+withDbState (DbHandle mvar) a = do
+	st <- liftIO $ takeMVar mvar
+	go st `onException` (liftIO $ putMVar mvar st)
+  where
+	go st = do
+		(v, st') <- a st
+		liftIO $ putMVar mvar st'
+		return v
+
+flushDbQueue :: DbHandle -> IO ()
+flushDbQueue (DbHandle mvar) = go =<< readMVar mvar
+  where
+	go (DbOpen qh) = H.flushDbQueue qh
+	go _ = return ()
diff --git a/Database/Keys/Types.hs b/Database/Keys/Types.hs
deleted file mode 100644
index 3fabafcf2..000000000
--- a/Database/Keys/Types.hs
+++ /dev/null
@@ -1,14 +0,0 @@
-{- Sqlite database of information about Keys, data types.
- -
- - Copyright 2015 Joey Hess <id@joeyh.name>
- -:
- - Licensed under the GNU GPL version 3 or higher.
- -}
-
-module Database.Keys.Types (
-	DbHandle(..)
-) where
-
-import qualified Database.Queue as H
-
-newtype DbHandle = DbHandle H.DbQueue