import qualified GHC.IO.Device as IODevice
import qualified GHC.IO.BufferedIO as Buffered
+import GHC.Conc
import GHC.Real
import GHC.Base
import GHC.Exception
withHandle' :: String -> Handle -> MVar Handle__
-> (Handle__ -> IO (Handle__,a)) -> IO a
withHandle' fun h m act =
- block $ do
- h_ <- takeMVar m
- checkHandleInvariants h_
- (h',v) <- (act h_ `catchAny` \err -> putMVar m h_ >> throw err)
- `catchException` \ex -> ioError (augmentIOError ex fun h)
+ block $ do
+ (h',v) <- do_operation fun h act m
checkHandleInvariants h'
putMVar m h'
return v
withHandle_ fun h@(DuplexHandle _ m _) act = withHandle_' fun h m act
withHandle_' :: String -> Handle -> MVar Handle__ -> (Handle__ -> IO a) -> IO a
-withHandle_' fun h m act =
- block $ do
- h_ <- takeMVar m
- checkHandleInvariants h_
- v <- (act h_ `catchAny` \err -> putMVar m h_ >> throw err)
- `catchException` \ex -> ioError (augmentIOError ex fun h)
- checkHandleInvariants h_
- putMVar m h_
- return v
+withHandle_' fun h m act = withHandle' fun h m $ \h_ -> do
+ a <- act h_
+ return (h_,a)
withAllHandles__ :: String -> Handle -> (Handle__ -> IO Handle__) -> IO ()
withAllHandles__ fun h@(FileHandle _ m) act = withHandle__' fun h m act
withHandle__' :: String -> Handle -> MVar Handle__ -> (Handle__ -> IO Handle__)
-> IO ()
withHandle__' fun h m act =
- block $ do
- h_ <- takeMVar m
- checkHandleInvariants h_
- h' <- (act h_ `catchAny` \err -> putMVar m h_ >> throw err)
- `catchException` \ex -> ioError (augmentIOError ex fun h)
+ block $ do
+ h' <- do_operation fun h act m
checkHandleInvariants h'
putMVar m h'
return ()
+do_operation :: String -> Handle -> (Handle__ -> IO a) -> MVar Handle__ -> IO a
+do_operation fun h act m = do
+ h_ <- takeMVar m
+ checkHandleInvariants h_
+ act h_ `catchException` handler h_
+ where
+ handler h_ e = do
+ putMVar m h_
+ case () of
+ _ | Just ioe <- fromException e ->
+ ioError (augmentIOError ioe fun h)
+ _ | Just async_ex <- fromException e -> do -- see Note [async]
+ let _ = async_ex :: AsyncException
+ t <- myThreadId
+ throwTo t e
+ do_operation fun h act m
+ _otherwise ->
+ throwIO e
+
+-- Note [async]
+--
+-- If an asynchronous exception is raised during an I/O operation,
+-- normally it is fine to just re-throw the exception synchronously.
+-- However, if we are inside an unsafePerformIO or an
+-- unsafeInterleaveIO, this would replace the enclosing thunk with the
+-- exception raised, which is wrong (#3997). We have to release the
+-- lock on the Handle, but what do we replace the thunk with? What
+-- should happen when the thunk is subsequently demanded again?
+--
+-- The only sensible choice we have is to re-do the IO operation on
+-- resumption, but then we have to be careful in the IO library that
+-- this is always safe to do. In particular we should
+--
+-- never perform any side-effects before an interruptible operation
+--
+-- because the interruptible operation may raise an asynchronous
+-- exception, which may cause the operation and its side effects to be
+-- subsequently performed again.
+--
+-- Re-doing the IO operation is achieved by:
+-- - using throwTo to re-throw the asynchronous exception asynchronously
+-- in the current thread
+-- - on resumption, it will be as if throwTo returns. In that case, we
+-- recursively invoke the original operation (see do_operation above).
+--
+-- Interruptible operations in the I/O library are:
+-- - threadWaitRead/threadWaitWrite
+-- - fillReadBuffer/flushWriteBuffer
+-- - readTextDevice/writeTextDevice
+
augmentIOError :: IOException -> String -> Handle -> IOException
augmentIOError ioe@IOError{ ioe_filename = fp } fun h
= ioe { ioe_handle = Just h, ioe_location = fun, ioe_filename = filepath }