[project @ 1999-01-16 16:06:17 by sof]

Documented isEmptyMVar

ghc/docs/libraries/Concurrent.sgml

@@ -22,8 +22,10 @@ takeMVar         :: MVar a -> IO a
 putMVar          :: MVar a -> a -> IO ()
 swapMVar         :: MVar a -> a -> IO a
 readMVar         :: MVar a -> IO a 
+isEmptyMVar      :: MVar a -> IO Bool
 instance Eq (MVar a)
 
+
 data Chan a      -- channels
 newChan          :: IO (Chan a)
 writeChan        :: Chan a -> a -> IO ()
@@ -97,4 +99,16 @@ its children before exiting.
 The <tt/Ord/ instance for <tt/ThreadId/s provides an arbitrary total ordering
 which might be used to build an ordered binary tree, say.  
 
+<item>
+The operation <tt/isEmptyMVar/ returns a flag indicating
+whether the <tt/MVar/ is currently empty or filled in, i.e.,
+will a thread block when performing a <tt/takeMVar/ on that
+<tt/MVar/ or not?
+
+Please notice that the Boolean value returned from <tt/isEmptyMVar/
+represent just a snapshot of the state of the <tt/MVar/. By the
+time a thread gets to inspect the result and act upon it, other
+threads may have accessed the <tt/MVar/ and changed its 'filled-in'
+status of the variable. Please be wary of this.
+
 </itemize>