Locks: Rework to avoid unnecessary display reopening

The extremely useful "Locks" plugin eats quite a lot of CPU (>2% here on a
old-ish laptop), unfortunately. The plug-in unnecessary reopens the
display, which is quite expensive operation. It results into 16 syscalls:

     socket(PF_LOCAL)      -> connect(sun_path=@"/tmp/.X11-unix/X0"})
  -> getpeername()         -> uname()
  -> access(".Xauthority") -> open(".Xauthority")
  -> fstat()               -> mmap()
  -> read()                -> close()
  -> munmap()              -> getsockname()
  -> fcntl(F_SETFD)        -> fcntl(F_SETFL)
  -> shutdown()            -> close()

This is almost half of all the syscalls that we ought to execute for the
plug-in to work. Now, considering the useful work and that "Locks" runs
every 200 milliseconds, it gives us >300 syscalls (and a lot more
wake-ups) per second.

This commit fixes the reopening issue, effectively halving the CPU
consumption (down to ~1%). The patch also makes it easier to implement
event-driven indicators that will reduce the idle CPU consumption to 0.

1 files changed, 19 insertions, 11 deletions

diff --git a/src/Plugins/Locks.hs b/src/Plugins/Locks.hs
index 3c1e0a9..b30eb1b 100644
--- a/src/Plugins/Locks.hs
+++ b/src/Plugins/Locks.hs
@@ -30,22 +30,30 @@ locks = [ ( xK_Caps_Lock,   "CAPS"   )
         , ( xK_Scroll_Lock, "SCROLL" )
         ]
 
+run' :: Display -> Window -> IO String
+run' d root = do
+    modMap <- getModifierMapping d
+    ( _, _, _, _, _, _, _, m ) <- queryPointer d root
+
+    ls <- filterM ( \( ks, _ ) -> do
+        kc <- keysymToKeycode d ks
+        return $ case find (elem kc . snd) modMap of
+            Nothing       -> False
+            Just ( i, _ ) -> testBit m (fromIntegral i)
+        ) locks
+
+    return $ unwords $ map snd ls
+
 instance Exec Locks where
     alias Locks = "locks"
     rate Locks = 2
-    run Locks = do
+    start Locks cb = do
         d <- openDisplay ""
         root <- rootWindow d (defaultScreen d)
 
-        modMap <- getModifierMapping d
-        ( _, _, _, _, _, _, _, m ) <- queryPointer d root
+        forever $ do
+            cb =<< run' d root
+            tenthSeconds $ rate Locks
 
-        ls <- filterM ( \( ks, _ ) -> do
-            kc <- keysymToKeycode d ks
-            return $ case find (elem kc . snd) modMap of
-                Nothing       -> False
-                Just ( i, _ ) -> testBit m (fromIntegral i)
-            ) locks
         closeDisplay d
-
-        return $ unwords $ map snd ls
+        return ()