Drain remaining var in response queue

Database/MongoDB/Internal/Protocol.hs

@@ -42,13 +42,13 @@ import Data.Bits (bit, testBit)
 import Data.Int (Int32, Int64)
 import Data.IORef (IORef, newIORef, atomicModifyIORef)
 import System.IO (Handle)
-import System.IO.Error (doesNotExistErrorType, mkIOError, ioError)
+import System.IO.Error (doesNotExistErrorType, mkIOError)
 import System.IO.Unsafe (unsafePerformIO)
 import Data.Maybe (maybeToList)
 import GHC.Conc (ThreadStatus(..), threadStatus)
 import Control.Monad (forever)
-import Control.Concurrent.Chan (Chan, newChan, readChan, writeChan)
+import Control.Concurrent.Chan (Chan, newChan, readChan, writeChan, isEmptyChan)
-import Control.Concurrent (ThreadId, forkIO, killThread, forkFinally)
+import Control.Concurrent (ThreadId, killThread, forkFinally)
 
 import Control.Exception.Lifted (onException, throwIO, try)
 
@@ -108,9 +108,25 @@ newPipeline serverData stream = do
     vStream <- newMVar stream
     responseQueue <- newChan
     finished <- newEmptyMVar
+    let drainReplies = do
+          chanEmpty <- isEmptyChan responseQueue
+          if chanEmpty
+            then return ()
+            else do
+              var <- readChan responseQueue
+              putMVar var $ Left $ mkIOError
+                                        doesNotExistErrorType
+                                        "Handle has been closed"
+                                        Nothing
+                                        Nothing
+              drainReplies
+
     rec
         let pipe = Pipeline{..}
-        listenThread <- forkFinally (listen pipe) (\_ -> putMVar finished ())
+        listenThread <- forkFinally (listen pipe) $ \_ -> do
+                                                       putMVar finished ()
+                                                       drainReplies
+
     _ <- mkWeakMVar vStream $ do
         killThread listenThread
         Tr.close stream
@@ -158,8 +174,8 @@ pcall :: Pipeline -> Message -> IO (IO Response)
 -- ^ Send message to destination and return /promise/ of response from one message only. The destination must reply to the message (otherwise promises will have the wrong responses in them).
 -- Throw IOError and closes pipeline if send fails, likewise for promised response.
 pcall p@Pipeline{..} message = do
-  finished <- isFinished p
+  listenerStopped <- isFinished p
-  if finished
+  if listenerStopped
     then ioError $ mkIOError doesNotExistErrorType "Handle has been closed" Nothing Nothing
     else withMVar vStream doCall `onException` close p
   where