mwm: Handle as many events as possible before redrawing

The current implementation redraws the monitors (where necessary) after
each handled event. This leads to problems when an application destroys
or unmaps multiple windows in one go, because mwm will attempt to redraw
the destroyed windows for which it hasn't processed the destroy/unmap
event yet.
This commit changes the mwm_run() function to handle all queued events
before redrawing anything.

diff --git a/mwm.c b/mwm.c
index 28203b23db4b7a1b39188040fb75d5309c319469..5bd9396c189d334f369c054ae6fd25fa1d3058c9 100644 (file)
--- a/mwm.c
+++ b/mwm.c
@@ -301,7 +301,9 @@ static void _mwm_destroy_notify(struct mwm *mwm, XDestroyWindowEvent *event)
        struct client *client;
 
        /* get the client and detach it */
+#if MWM_DEBUG
        printf("%s(%p, %p)\n", __func__, (void*)mwm, (void*)event);
+#endif /* MWM_DEBUG */
 
        if(mwm_find_client(mwm, FIND_CLIENT_BY_WINDOW,
                           &event->window, &client) < 0) {
@@ -507,7 +509,9 @@ static void _mwm_unmap_notify(struct mwm *mwm, XUnmapEvent *event)
 {
        struct client *client;
 
+#if MWM_DEBUG
        printf("%s(%p, %p)\n", __func__, (void*)mwm, (void*)event);
+#endif /* MWM_DEBUG */
 
         if(mwm_find_client(mwm, FIND_CLIENT_BY_WINDOW,
                            &event->window, &client) < 0) {
@@ -515,6 +519,7 @@ static void _mwm_unmap_notify(struct mwm *mwm, XUnmapEvent *event)
        }
 
        XGrabServer(mwm->display);
+       XSync(mwm->display, False);
        XSetErrorHandler(_xerror_nop);
 
        client_set_state(client, WithdrawnState);
@@ -1039,13 +1044,25 @@ int mwm_run(struct mwm *mwm)
        XSync(mwm->display, False);
        mwm->running = 1;
 
-       while(mwm->running && !XNextEvent(mwm->display, &event)) {
+       while(mwm->running) {
                struct client *focused_client;
 
-               if(mwm->xhandler[event.type]) {
-                       /* printf("XEvent: %x\n", event.type); */
-                       mwm->xhandler[event.type](mwm, &event);
-               }
+               /*
+                * Handle as many events as possible before redrawing. This is necessary
+                * to avoid problems where an application unmaps/destroys multiple windows
+                * in one go. If we process the events one-by-one, redrawing after each
+                * event, we will likely attempt to redraw a window that was already
+                * unmapped or destroyed, we just haven't noticed it yet because the event
+                * is still in the queue.
+                */
+
+               do {
+                       if(XNextEvent(mwm->display, &event) == 0) {
+                               if(mwm->xhandler[event.type]) {
+                                       mwm->xhandler[event.type](mwm, &event);
+                               }
+                       }
+               } while(XEventsQueued(mwm->display, QueuedAfterFlush) > 0);
 
                if(mwm->needs_redraw) {
                        mwm_redraw(mwm);