add some 'IO' variants

Control/Concurrent/STM/TMVar.hs

@@ -32,10 +32,12 @@ module Control.Concurrent.STM.TMVar (
         readTMVar,
         writeTMVar,
         tryReadTMVar,
+        tryReadTMVarIO,
         swapTMVar,
         tryTakeTMVar,
         tryPutTMVar,
         isEmptyTMVar,
+        isEmptyTMVarIO,
         mkWeakTMVar
 #endif
   ) where
@@ -141,6 +143,17 @@ readTMVar (TMVar t) = do
 tryReadTMVar :: TMVar a -> STM (Maybe a)
 tryReadTMVar (TMVar t) = readTVar t
 
+-- | A version of 'readTMVar' which does not retry. This is
+-- equivalent to
+--
+-- >  readTVarIO = atomically . readTVar
+--
+-- but works much faster, because it doesn't perform a complete
+-- transaction, it just attempts to read the current value of
+-- the 'TMVar'.
+tryReadTMVarIO :: TMVar a -> IO (Maybe a)
+tryReadTMVarIO (TMVar t) = readTVarIO t
+
 -- |Swap the contents of a 'TMVar' for a new value.
 swapTMVar :: TMVar a -> a -> STM a
 swapTMVar (TMVar t) new = do
@@ -164,6 +177,14 @@ isEmptyTMVar (TMVar t) = do
     Nothing -> return True
     Just _  -> return False
 
+-- |@IO@ version of 'isEmptyTVar'.
+isEmptyTMVarIO :: TMVar a -> IO Bool
+isEmptyTMVarIO (TMVar t) = do
+  m <- readTVarIO t
+  case m of
+    Nothing -> return True
+    Just _  -> return False
+
 -- | Make a 'Weak' pointer to a 'TMVar', using the second argument as
 -- a finalizer to run when the 'TMVar' is garbage-collected.
 --

Control/Concurrent/STM/TSem.hs

@@ -17,6 +17,7 @@
 module Control.Concurrent.STM.TSem
   ( TSem
   , newTSem
+  , newTSemIO
 
   , waitTSem
 
@@ -59,6 +60,10 @@ newtype TSem = TSem (TVar Integer)
 newTSem :: Integer -> STM TSem
 newTSem i = fmap TSem (newTVar $! i)
 
+-- |@IO@ equivalent of 'newTSem'.
+newTSemIO :: Integer -> IO TSem
+newTSemIO i = fmap TSem (newTVarIO $! i)
+
 -- NOTE: we can't expose a good `TSem -> STM Int' operation as blocked
 -- 'waitTSem' aren't reliably reflected in a negative counter value.