6fcccbba19Now that ghc 9.0.2 is the oldest supported version. Eg cruft from https://web.archive.org/web/20190424185034/https://prime.haskell.org/wiki/Libraries/Proposals/SemigroupMonoid Sponsored-by: Jack Hill
74 lines
1.8 KiB
Haskell
74 lines
1.8 KiB
Haskell
{- Handle for the Keys database.
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-
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- Copyright 2015 Joey Hess <id@joeyh.name>
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-:
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- Licensed under the GNU AGPL version 3 or higher.
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-}
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module Database.Keys.Handle (
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DbHandle,
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newDbHandle,
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DbState(..),
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DbWasOpen(..),
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withDbState,
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flushDbQueue,
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closeDbHandle,
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) where
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import qualified Database.Queue as H
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import Database.Keys.Tables
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import Utility.Exception
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import Utility.DebugLocks
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import Control.Concurrent
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import Control.Monad.IO.Class (liftIO, MonadIO)
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-- The MVar is always left full except when actions are run
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-- that access the database.
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newtype DbHandle = DbHandle (MVar DbState)
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-- The database can be closed or open, but it also may have been
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-- tried to open (for read) and didn't exist yet or is not readable.
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data DbState
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= DbClosed DbWasOpen
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| DbOpen (H.DbQueue, DbTablesChanged)
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| DbUnavailable
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-- Was the database previously opened by this process?
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data DbWasOpen = DbWasOpen Bool
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newDbHandle :: IO DbHandle
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newDbHandle = DbHandle <$> newMVar (DbClosed (DbWasOpen False))
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-- Runs an action on the state of the handle, which can change its state.
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-- The MVar is empty while the action runs, which blocks other users
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-- of the handle from running.
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withDbState
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:: (MonadIO m, MonadCatch m)
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=> DbHandle
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-> (DbState -> m (v, DbState))
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-> m v
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withDbState (DbHandle mvar) a = do
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st <- liftIO $ debugLocks $ takeMVar mvar
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go st `onException` (liftIO $ debugLocks $ putMVar mvar st)
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where
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go st = do
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(v, st') <- a st
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liftIO $ debugLocks $ putMVar mvar st'
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return v
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flushDbQueue :: DbHandle -> IO ()
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flushDbQueue h = withDbState h go
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where
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go (DbOpen (qh, _)) = do
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H.flushDbQueue qh
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return ((), DbOpen (qh, mempty))
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go st = return ((), st)
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closeDbHandle :: DbHandle -> IO ()
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closeDbHandle h = withDbState h go
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where
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go (DbOpen (qh, _)) = do
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H.closeDbQueue qh
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return ((), DbClosed (DbWasOpen True))
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go st = return ((), st)
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