diff options
| -rw-r--r-- | libraries/base/Control/Concurrent/Chan.hs | 11 |
1 files changed, 1 insertions, 10 deletions
diff --git a/libraries/base/Control/Concurrent/Chan.hs b/libraries/base/Control/Concurrent/Chan.hs index d752a898f0..d0fed4a405 100644 --- a/libraries/base/Control/Concurrent/Chan.hs +++ b/libraries/base/Control/Concurrent/Chan.hs @@ -106,21 +106,12 @@ writeChan (Chan _ writeVar) val = do -- thread holds a reference to the channel. readChan :: Chan a -> IO a readChan (Chan readVar _) = do - modifyMVarMasked readVar $ \read_end -> do -- Note [modifyMVarMasked] + modifyMVar readVar $ \read_end -> do (ChItem val new_read_end) <- readMVar read_end -- Use readMVar here, not takeMVar, -- else dupChan doesn't work return (new_read_end, val) --- Note [modifyMVarMasked] --- This prevents a theoretical deadlock if an asynchronous exception --- happens during the readMVar while the MVar is empty. In that case --- the read_end MVar will be left empty, and subsequent readers will --- deadlock. Using modifyMVarMasked prevents this. The deadlock can --- be reproduced, but only by expanding readMVar and inserting an --- artificial yield between its takeMVar and putMVar operations. - - -- |Duplicate a 'Chan': the duplicate channel begins empty, but data written to -- either channel from then on will be available from both. Hence this creates -- a kind of broadcast channel, where data written by anyone is seen by |