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{- Pinpointing location of MVar/STM deadlocks
-
- Copyright 2018 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Utility.DebugLocks (debugLocks) where
import Control.Monad.Catch
import Control.Monad.IO.Class
#ifdef DEBUGLOCKS
import Control.Exception (BlockedIndefinitelyOnSTM, BlockedIndefinitelyOnMVar)
import GHC.Stack
import System.IO
#endif
{- Wrap around any action, and if it dies due to deadlock, will display
- a call stack on stderr when DEBUGLOCKS is defined.
-
- Should be zero cost to call when DEBUGLOCKS is not defined.
-}
#ifdef DEBUGLOCKS
debugLocks :: HasCallStack => (MonadCatch m, MonadIO m) => m a -> m a
debugLocks a = a `catches`
[ Handler (\ (e :: BlockedIndefinitelyOnMVar) -> go "MVar" e callStack)
, Handler (\ (e :: BlockedIndefinitelyOnSTM) -> go "STM" e callStack)
]
where
go ty e cs = do
liftIO $ do
hPutStrLn stderr $
ty ++ " deadlock detected " ++ prettyCallStack cs
hFlush stderr
throwM e
#else
-- No HasCallStack constraint.
debugLocks :: (MonadCatch m, MonadIO m) => m a -> m a
debugLocks a = a
#endif
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