IOCP.FFI: make queryPerformanceCounter throw an exception on failure

QueryPerformanceCounter is not expected to fail after
QueryPerformanceFrequency succeeded.

Author: joeyadams

IOCP/FFI.hsc

@@ -222,15 +222,20 @@ callQP qpfunc =
 --
 -- Problems:
 --
+--  * Might not be available on some hardware.  Use 'queryPerformanceFrequency'
+--    to test for availability before calling this function.
+--
 --  * On a multiprocessor computer, may produce different results on
 --    different processors due to hardware bugs.
 --
 -- To get a monotonic time in seconds, divide the result of
 -- 'queryPerformanceCounter' by that of 'queryPerformanceFrequency'.
 --
 -- <http://msdn.microsoft.com/en-us/library/windows/desktop/ms644904%28v=vs.85%29.aspx>
-queryPerformanceCounter :: IO (Maybe Int64)
-queryPerformanceCounter = callQP c_QueryPerformanceCounter
+queryPerformanceCounter :: IO Int64
+queryPerformanceCounter =
+    callQP c_QueryPerformanceCounter
+    >>= maybe (Win32.errorWin "QueryPerformanceCounter") return
 
 -- | Call the @QueryPerformanceFrequency@ function.  Return 'Nothing' if the
 -- hardware does not provide a high-resolution performance counter.

testing/monotonic-time.hs

@@ -29,7 +29,7 @@ main = do
             t64 <- maybe (return Nothing) (fmap Just) gtc64
             qpc <- case freq of
                 Nothing -> return Nothing
-                Just f  -> fmap (\c -> (c, f)) <$> queryPerformanceCounter
+                Just f  -> (\c -> Just (c, f)) <$> queryPerformanceCounter
             putStrLn $ formatTimes t t64 qpc
 
         formatTimes t t64 qpc =