winio: Remove outstanding_requests from runner.

We used a variable to keep track of situations where we got
entries from the IO port, but all of them had already been
canceled. While we can avoid some work that way this case
seems quite rare.

So we give up on tracking this and instead always assume at
least one of the returned entries is valid.

If that's not the case no harm is done, we just perform some
additional work. But it makes the runner easier to reason about.

In particular we don't need to care if another thread modifies
oustanding_requests after we return from waiting on the IO Port.

1 files changed, 1 insertions, 3 deletions

diff --git a/libraries/base/GHC/Event/Windows.hsc b/libraries/base/GHC/Event/Windows.hsc
index ccdc6e1144..113f0c0eb9 100644
--- a/libraries/base/GHC/Event/Windows.hsc
+++ b/libraries/base/GHC/Event/Windows.hsc
@@ -396,9 +396,7 @@ startIOManagerThread loop
   | otherwise = do
     modifyMVar_ ioManagerThread $ \old -> do
       let create = do debugIO "spawning worker threads.."
-                      t <- if threadedIOMgr
-                              then forkOS loop
-                              else forkIO loop
+                      t <- forkOS loop
                       debugIO $ "created io-manager threads."
                       labelThread t "IOManagerThread"
                       return (Just t)