Simplified UpdateStream.pull

1 files changed, 9 insertions, 8 deletions

diff --git a/Control/Concurrent/STM/UpdateStream.hs b/Control/Concurrent/STM/UpdateStream.hs
index 502abefb..b01fc0bc 100644
--- a/Control/Concurrent/STM/UpdateStream.hs
+++ b/Control/Concurrent/STM/UpdateStream.hs
@@ -115,6 +115,11 @@ new isStart isStop = do
 -- starts with the same slot value.  Otherwise, the chunk is preserved.  Note
 -- that the same slot value must be passed again for every chunk of the message
 -- as it is not remembered.
+--
+-- Note that although a slot value is provided on each push, it is assumed that
+-- messages will be pushed in contiguous streams.  To change this, we would
+-- need to add a mutable integer to track the nesting level of the primary
+-- (non-slotted) stream.
 push :: Ord slot => UpdateStream slot x -> Maybe slot -> x -> STM ()
 push u Nothing x = writeTChan (events u) x
 push u (Just n) x = do
@@ -135,19 +140,15 @@ push u (Just n) x = do
 -- and discarded when new messages are 'push'ed.
 pull :: Ord slot => UpdateStream slot x -> STM x
 pull u = do
-    (inm, mbscache) <- do
-        mn <- readTVar $ inMessage u
-        -- map <- readTVar (cache u)
-        return $ (isJust mn, mn) --  mn >>= flip Map.lookup map)
+    mbscache <- readTVar $ inMessage u
     let action =
-         case (inm,mbscache) of
-            (True,Just scache) -> do
+         case mbscache of
+            Just scache -> do
                 x <- Status.pull scache
                 nesting <- readTVar (Status.pullDepth scache)
                 when (nesting==0) $ writeTVar (inMessage u) Nothing
                 return x
-            (True,Nothing)     -> readTChan (events u)
-            (False,_) -> do
+            Nothing -> do
                 cs <- fmap (Map.toList) $ readTVar (cache u)
                 cs <- filterM (return . not <=< Status.isEmpty . snd)
                               cs