Add a test for black hole behaviour, where a computation is shared
between threads.
--- /dev/null
+module Main where
+
+import Concurrent
+
+-- This test hopefully exercises the black hole code. The main thread
+-- forks off another thread and starts on a large computation.
+-- The child thread attempts to get the result of the same large
+-- computation (and should get blocked doing so, because the parent
+-- won't have evaluated it yet). When the result is available, the
+-- child passes it back to the parent who prints it out.
+
+test = sum [1..10000]
+
+main = do
+ x <- newEmptyMVar
+ forkIO (if test > 0
+ then putMVar x test
+ else error "proc"
+ )
+ if test > 0 -- evaluate test
+ then do result <- takeMVar x
+ print result
+ else error "main"