-- | Concurrent Logging
module Control.Eff.Log.Channel
( LogChannel()
, logToChannel
, noLogger
, forkLogger
, filterLogChannel
, joinLogChannel
, killLogChannel
, closeLogChannelAfter
, logChannelBracket
, logChannelPutIO
, JoinLogChannelException()
, KillLogChannelException()
)
where
import Control.Concurrent
import Control.Concurrent.STM
import Control.Eff as Eff
import Control.Exception ( bracket )
import qualified Control.Exception as Exc
import Control.Monad ( void
, when
, unless
)
import Control.Monad.Log as ExtLog
hiding ( )
import Control.Monad.Trans.Control
import Control.Eff.Log.Handler
import qualified Control.Eff.Lift as Eff
import Data.Foldable ( traverse_ )
import Data.Kind ( )
import Data.String
import Data.Typeable
-- | A log channel processes logs from the 'Logs' effect by en-queuing them in a
-- shared queue read from a seperate processes. A channel can contain log
-- message filters.
data LogChannel message =
FilteredLogChannel (message -> Bool) (LogChannel message)
-- ^ filter log messages
| DiscardLogs
-- ^ discard all log messages
| ConcurrentLogChannel
{ fromLogChannel :: TBQueue message
, _logChannelThread :: ThreadId
}
-- ^ send all log messages to a log process
-- | Send the log messages to a 'LogChannel'.
logToChannel
:: forall r message a
. (SetMember Eff.Lift (Eff.Lift IO) r)
=> LogChannel message
-> Eff (Logs message ': r) a
-> Eff r a
logToChannel logChan =
handleLogsWithLoggingTHandler ($ logChannelPutIO logChan)
-- | Enqueue a log message into a log channel
logChannelPutIO :: LogChannel message -> message -> IO ()
logChannelPutIO DiscardLogs _ = return ()
logChannelPutIO (FilteredLogChannel f lc) m = when (f m) (logChannelPutIO lc m)
logChannelPutIO c m = atomically $ do
dropMessage <- isFullTBQueue (fromLogChannel c)
unless dropMessage (writeTBQueue (fromLogChannel c) m)
-- | Create a 'LogChannel' that will discard all messages sent
-- via 'forwardLogstochannel' or 'logChannelPutIO'.
noLogger :: LogChannel message
noLogger = DiscardLogs
-- | Fork a new process, that applies a monadic action to all log messages sent
-- via 'logToChannel' or 'logChannelPutIO'.
forkLogger
:: forall message
. (Typeable message)
=> Int -- ^ Size of the log message input queue. If the queue is full, message
-- are dropped silently.
-> (message -> IO ()) -- ^ An IO action to log the messages
-> Maybe message -- ^ Optional __first__ message to log
-> IO (LogChannel message)
forkLogger queueLen handle mFirstMsg = do
msgQ <- atomically
(do
tq <- newTBQueue (fromIntegral @Int queueLen)
mapM_ (writeTBQueue tq) mFirstMsg
return tq
)
thread <- forkFinally (logLoop msgQ) (writeLastLogs msgQ)
return (ConcurrentLogChannel msgQ thread)
where
writeLastLogs :: TBQueue message -> Either Exc.SomeException () -> IO ()
writeLastLogs tq ee = do
logMessages <- atomically $ flushTBQueue tq
case ee of
Right _ -> return ()
Left se -> case Exc.fromException se of
Just JoinLogChannelException -> traverse_ handle logMessages
Nothing -> case Exc.fromException se of
Just KillLogChannelException -> return ()
Nothing -> mapM_ handle logMessages
logLoop :: TBQueue message -> IO ()
logLoop tq = do
m <- atomically $ readTBQueue tq
handle m
logLoop tq
-- | Filter logs sent to a 'LogChannel' using a predicate.
filterLogChannel
:: (message -> Bool) -> LogChannel message -> LogChannel message
filterLogChannel = FilteredLogChannel
-- | Run an action and close a 'LogChannel' created by 'noLogger', 'forkLogger'
-- or 'filterLogChannel' afterwards using 'joinLogChannel'. If a
-- 'Exc.SomeException' was thrown, the log channel is killed with
-- 'killLogChannel', and the exception is re-thrown.
closeLogChannelAfter
:: (Typeable message, IsString message) => LogChannel message -> IO a -> IO a
closeLogChannelAfter logC ioAction = do
res <- closeLogAndRethrow `Exc.handle` ioAction
closeLogSuccess
return res
where
closeLogAndRethrow :: Exc.SomeException -> IO a
closeLogAndRethrow se = do
void $ Exc.try @Exc.SomeException $ killLogChannel logC
Exc.throw se
closeLogSuccess :: IO ()
closeLogSuccess = joinLogChannel logC
-- | Close a log channel created by e.g. 'forkLogger'. Message already enqueue
-- are handled. Subsequent log message
-- will not be handled anymore. If the log channel must be closed immediately,
-- use 'killLogChannel' instead.
joinLogChannel :: (Typeable message) => LogChannel message -> IO ()
joinLogChannel DiscardLogs = return ()
joinLogChannel (FilteredLogChannel _f lc) = joinLogChannel lc
joinLogChannel (ConcurrentLogChannel _tq thread) =
throwTo thread JoinLogChannelException
-- | Close a log channel quickly, without logging messages already in the queue.
-- Subsequent logging requests will not be handled anymore. If the log channel
-- must be closed without loosing any messages, use 'joinLogChannel' instead.
killLogChannel :: (Typeable message) => LogChannel message -> IO ()
killLogChannel DiscardLogs = return ()
killLogChannel (FilteredLogChannel _f lc) = killLogChannel lc
killLogChannel (ConcurrentLogChannel _tq thread) =
throwTo thread KillLogChannelException
-- | Internal exception to shutdown a 'LogChannel' process created by
-- 'forkLogger'. This exception is handled such that all message already
-- en-queued are handled and then an optional final message is written.
data JoinLogChannelException = JoinLogChannelException
deriving (Show, Typeable)
instance Exc.Exception JoinLogChannelException
-- | Internal exception to **immediately** shutdown a 'LogChannel' process
-- created by 'forkLogger', other than 'JoinLogChannelException' the message queue
-- will not be flushed, not further messages will be logged, except for the
-- optional final message.
data KillLogChannelException = KillLogChannelException
deriving (Show, Typeable)
instance Exc.Exception KillLogChannelException
-- | Wrap 'LogChannel' creation and destruction around a monad action in
-- 'bracket'y manner. This function uses 'joinLogChannel', so en-queued messages
-- are flushed on exit. The resulting action is a 'LoggingT' action, which
-- is essentially a reader for a log handler function in 'IO'.
logChannelBracket
:: (Typeable message)
=> Int -- ^ Size of the log message input queue. If the queue is full, message
-- are dropped silently.
-> Maybe message -- ^ Optional __first__ message to log
-> (LogChannel message -> IO a) -- ^ An IO action that will use the
-- 'LogChannel', after the action returns (even
-- because of an exception) the log channel is
-- destroyed.
-> LoggingT message IO a
logChannelBracket queueLen mWelcome f = control
(\runInIO -> do
let logHandler = void . runInIO . logMessage
bracket (forkLogger queueLen logHandler mWelcome) joinLogChannel f
)