[commit: stm] master: Control.Concurrent.STM.TMVar: added tryReadTMVar (86b8629)

[Simon Marlow]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/stm

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/86b8629bebf53f00afb641e0a9b2cb3eff7b38d3

>---------------------------------------------------------------

commit 86b8629bebf53f00afb641e0a9b2cb3eff7b38d3
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Mon Apr 11 11:06:05 2011 +0100

    Control.Concurrent.STM.TMVar: added tryReadTMVar

>---------------------------------------------------------------

 Control/Concurrent/STM/TMVar.hs |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/Control/Concurrent/STM/TMVar.hs b/Control/Concurrent/STM/TMVar.hs
index 0a43b0a..05c83f6 100644
--- a/Control/Concurrent/STM/TMVar.hs
+++ b/Control/Concurrent/STM/TMVar.hs
@@ -26,6 +26,7 @@ module Control.Concurrent.STM.TMVar (
 	takeTMVar,
 	putTMVar,
 	readTMVar,	
+	tryReadTMVar,
 	swapTMVar,
 	tryTakeTMVar,
 	tryPutTMVar,
@@ -115,10 +116,9 @@ tryPutTMVar (TMVar t) a = do
     Nothing -> do writeTVar t (Just a); return True
     Just _  -> return False
 
-{-|
-  This is a combination of 'takeTMVar' and 'putTMVar'; ie. it takes the value
-  from the 'TMVar', puts it back, and also returns it.
--}
+-- | This is a combination of 'takeTMVar' and 'putTMVar'; ie. it
+-- takes the value from the 'TMVar', puts it back, and also returns
+-- it.
 readTMVar :: TMVar a -> STM a
 readTMVar (TMVar t) = do
   m <- readTVar t
@@ -126,6 +126,10 @@ readTMVar (TMVar t) = do
     Nothing -> retry
     Just a  -> return a
 
+-- | Non-blocking version of 'readTMVar'.
+tryReadTMVar :: TMVar a -> STM (Maybe a)
+tryReadTMVar (TMVar t) = readTVar t
+
 -- |Swap the contents of a 'TMVar' for a new value.
 swapTMVar :: TMVar a -> a -> STM a
 swapTMVar (TMVar t) new = do