From 7064cb084ea05f13a54ec7cfb2956f5ade5458ba Mon Sep 17 00:00:00 2001
From: Andrea Rossato <andrea.rossato@ing.unitn.it>
Date: Thu, 11 Oct 2007 22:30:29 +0200
Subject: The MVar is needed to avoid a race condition

As Spencer noted the checker thread may be throwing an exception
immediately, thus producing a race condition.

darcs-hash:20071011203029-d6583-64a79e4be3cf1ab97c7ba2ee36db08166c9003d4.gz
---
 Xmobar.hs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Xmobar.hs b/Xmobar.hs
index ac7ca40..e8091a7 100644
--- a/Xmobar.hs
+++ b/Xmobar.hs
@@ -70,11 +70,12 @@ runX c d w f = runReaderT f (XConf d w c)
 
 -- | The event loop
 eventLoop :: Config -> [(Maybe ThreadId, TVar String)] -> Display -> Window -> IO ()
-eventLoop c v d w = block $ do
+eventLoop c v d w = do
+    b  <- newEmptyMVar
     tv <- atomically $ newTVar []
-    t  <- myThreadId
-    forkIO $ checker t tv ""
-    go tv
+    t  <- forkIO (block $ do putMVar b (); go tv)
+    takeMVar b
+    checker t tv ""
  where
     -- interrupt the drawing thread every time a var is updated
     checker t tvar ov = do
-- 
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