getEps :: TcRnIf gbl lcl ExternalPackageState
getEps = do { env <- getTopEnv; readMutVar (hsc_EPS env) }
--- Updating the EPS. This should be an atomic operation.
--- Note the delicate 'seq' which forces the EPS before putting it in the
--- variable. Otherwise what happens is that we get
--- write eps_var (....(unsafeRead eps_var)....)
--- and if the .... is strict, that's obviously bottom. By forcing it beforehand
--- we make the unsafeRead happen before we update the variable.
-
+-- | Update the external package state. Returns the second result of the
+-- modifier function.
+--
+-- This is an atomic operation and forces evaluation of the modified EPS in
+-- order to avoid space leaks.
updateEps :: (ExternalPackageState -> (ExternalPackageState, a))
-> TcRnIf gbl lcl a
-updateEps upd_fn = do { traceIf (text "updating EPS")
- ; eps_var <- getEpsVar
- ; eps <- readMutVar eps_var
- ; let { (eps', val) = upd_fn eps }
- ; seq eps' (writeMutVar eps_var eps')
- ; return val }
+updateEps upd_fn = do
+ traceIf (text "updating EPS")
+ eps_var <- getEpsVar
+ atomicUpdMutVar' eps_var upd_fn
+-- | Update the external package state.
+--
+-- This is an atomic operation and forces evaluation of the modified EPS in
+-- order to avoid space leaks.
updateEps_ :: (ExternalPackageState -> ExternalPackageState)
-> TcRnIf gbl lcl ()
-updateEps_ upd_fn = do { traceIf (text "updating EPS_")
- ; eps_var <- getEpsVar
- ; eps <- readMutVar eps_var
- ; let { eps' = upd_fn eps }
- ; seq eps' (writeMutVar eps_var eps') }
+updateEps_ upd_fn = do
+ traceIf (text "updating EPS_")
+ eps_var <- getEpsVar
+ atomicUpdMutVar' eps_var (\eps -> (upd_fn eps, ()))
getHpt :: TcRnIf gbl lcl HomePackageTable
getHpt = do { env <- getTopEnv; return (hsc_HPT env) }
tryM, tryAllM, tryMostM, fixM,
-- I/O operations
- IORef, newMutVar, readMutVar, writeMutVar, updMutVar
+ IORef, newMutVar, readMutVar, writeMutVar, updMutVar,
+ atomicUpdMutVar, atomicUpdMutVar'
) where
import Exception
import Panic
-import Data.IORef ( IORef, newIORef, readIORef, writeIORef, modifyIORef )
+import Data.IORef ( IORef, newIORef, readIORef, writeIORef, modifyIORef,
+ atomicModifyIORef )
import Data.Typeable
import System.IO.Unsafe ( unsafeInterleaveIO )
import System.IO ( fixIO )
updMutVar :: IORef a -> (a -> a) -> IOEnv env ()
updMutVar var upd = liftIO (modifyIORef var upd)
+-- | Atomically update the reference. Does not force the evaluation of the
+-- new variable contents. For strict update, use 'atomicUpdMutVar''.
+atomicUpdMutVar :: IORef a -> (a -> (a, b)) -> IOEnv env b
+atomicUpdMutVar var upd = liftIO (atomicModifyIORef var upd)
+
+-- | Strict variant of 'atomicUpdMutVar'.
+atomicUpdMutVar' :: IORef a -> (a -> (a, b)) -> IOEnv env b
+atomicUpdMutVar' var upd = do
+ r <- atomicUpdMutVar var upd
+ _ <- liftIO . evaluate =<< readMutVar var
+ return r
----------------------------------------------------------------------
-- Accessing the environment