isClosed Pipeline used to hang because it was waiting on listen loop's read to finish. Now isClosed tests if listen loop has ended

Control/Pipeline.hs

@@ -1,8 +1,8 @@
 {- | Pipelining is sending multiple requests over a socket and receiving the responses later, in the same order. This is faster than sending one request, waiting for the response, then sending the next request, and so on. This implementation returns a /promise (future)/ response for each request that when invoked waits for the response if not already arrived. Multiple threads can send on the same pipeline (and get promises back); it will pipeline each thread's request right away without waiting.
 
-A pipeline closes itself when a read or write causes an error, so you can detect a broken pipeline by checking isClosed. -}
+A pipeline closes itself when a read or write causes an error, so you can detect a broken pipeline by checking isClosed.  It also closes itself when garbage collected, or you can close it explicitly. -}
 
-{-# LANGUAGE DoRec, RecordWildCards, MultiParamTypeClasses, FlexibleContexts #-}
+{-# LANGUAGE DoRec, RecordWildCards, NamedFieldPuns, MultiParamTypeClasses, FlexibleContexts #-}
 
 module Control.Pipeline (
 	-- * Pipeline
@@ -25,6 +25,7 @@ import qualified Data.ByteString as S
 import qualified Data.ByteString.Lazy as L
 import Data.Monoid (Monoid(..))
 import Control.Concurrent (ThreadId, forkIO, killThread)
+import GHC.Conc (ThreadStatus(..), threadStatus)
 import Control.Concurrent.MVar
 import Control.Concurrent.Chan
 
@@ -120,7 +121,14 @@ instance (Resource IO h) => Resource IO (Pipeline h b) where
 	close Pipeline{..} = do
 		killThread listenThread
 		close =<< readMVar vHandle
-	isClosed Pipeline{..} = isClosed =<< readMVar vHandle
+	isClosed Pipeline{listenThread} = do
+		status <- threadStatus listenThread
+		return $ case status of
+			ThreadRunning -> False
+			ThreadFinished -> True
+			ThreadBlocked _ -> False
+			ThreadDied -> True
+	--isClosed Pipeline{..} = isClosed =<< readMVar vHandle  -- isClosed hangs while listen loop is waiting on read
 
 listen :: (Stream h b, Resource IO h) => Pipeline h b -> IO ()
 -- ^ Listen for responses and supply them to waiting threads in order