[project @ 1998-07-27 12:38:33 by simonm]

Add a test for black hole behaviour, where a computation is shared
between threads.

ghc/tests/concurrent/should_run/conc006.hs

+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"

ghc/tests/concurrent/should_run/conc006.stdout

+50005000