withMVar family have a bug

withMVar is defined like this:

withMVar :: MVar a -> (a -> IO b) -> IO b
withMVar m io = 
  block $ do
    a <- takeMVar m
    b <- catch (unblock (io a))
      	    (\e -> do putMVar m a; throw e)
    putMVar m a
    return b

unfortunately this has a (very rare) bug: catch can raise a stack overflow exception, which would leave the MVar empty.

This is a tricky one. Perhaps in the event of a stack overflow, catch should ensure that the exception is passed directly to its handler, and we always add some extra stack space for the handler.

Trac metadata

Trac field	Value
Version	6.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown