[commit: stm] master: Throw an exception when reading from a broadcast channel (#7218) (4965c01)

[Simon Marlow]

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

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/4965c0139de186c8322cb48b52550acb4b8d9afa

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

commit 4965c0139de186c8322cb48b52550acb4b8d9afa
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Thu Sep 6 09:46:20 2012 +0100

    Throw an exception when reading from a broadcast channel (#7218)

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

 Control/Concurrent/STM/TChan.hs |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/Control/Concurrent/STM/TChan.hs b/Control/Concurrent/STM/TChan.hs
index 52af426..455dafe 100644
--- a/Control/Concurrent/STM/TChan.hs
+++ b/Control/Concurrent/STM/TChan.hs
@@ -97,9 +97,8 @@ newTChanIO = do
 -- garbage collected after clients have seen them.
 newBroadcastTChan :: STM (TChan a)
 newBroadcastTChan = do
-    dummy_hole <- newTVar TNil
     write_hole <- newTVar TNil
-    read <- newTVar dummy_hole
+    read <- newTVar (error "reading from a TChan created by newBroadcastTChan; use dupTChan first")
     write <- newTVar write_hole
     return (TChan read write)