Make gdk_event_apply_filters safe against changes in filter list

An event filter may add or remove filters itself.  This patch does
two things to address this case.  The first is to take a temporary
reference to the filter while it is being used.  The second is
to wait until after the filter function is run before determining
the next node in the list to process.  This guards against
changes to the next node.  It also does not run functions
that have been marked as removed.  Though I'm not sure if this
case can arise.

https://bugzilla.gnome.org/show_bug.cgi?id=635380

gdk/gdkinternals.h

@@ -59,9 +59,15 @@ struct _GdkColorInfo
   guint ref_count;
 };
 
+typedef enum {
+  GDK_EVENT_FILTER_REMOVED = 1 << 0
+} GdkEventFilterFlags;
+
 struct _GdkEventFilter {
   GdkFilterFunc function;
   gpointer data;
+  GdkEventFilterFlags flags;
+  guint ref_count;
 };
 
 struct _GdkClientFilter {

gdk/gdkwindow.c

@@ -2577,13 +2577,18 @@ gdk_window_add_filter (GdkWindow     *window,
     {
       filter = (GdkEventFilter *)tmp_list->data;
       if ((filter->function == function) && (filter->data == data))
-	return;
+        {
+          filter->ref_count++;
+          return;
+        }
       tmp_list = tmp_list->next;
     }
 
   filter = g_new (GdkEventFilter, 1);
   filter->function = function;
   filter->data = data;
+  filter->ref_count = 1;
+  filter->flags = 0;
 
   if (private)
     private->filters = g_list_append (private->filters, filter);
@@ -2626,6 +2631,11 @@ gdk_window_remove_filter (GdkWindow     *window,
 
       if ((filter->function == function) && (filter->data == data))
 	{
+          filter->flags |= GDK_EVENT_FILTER_REMOVED;
+          filter->ref_count--;
+          if (filter->ref_count != 0)
+            return;
+
 	  if (private)
 	    private->filters = g_list_remove_link (private->filters, node);
 	  else

gdk/quartz/gdkevents-quartz.c

@@ -171,19 +171,40 @@ append_event (GdkEvent *event,
 static gint
 gdk_event_apply_filters (NSEvent *nsevent,
 			 GdkEvent *event,
-			 GList *filters)
+			 GList **filters)
 {
   GList *tmp_list;
   GdkFilterReturn result;
   
-  tmp_list = filters;
+  tmp_list = *filters;
 
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter*) tmp_list->data;
-      
-      tmp_list = tmp_list->next;
+      GList *node;
+
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (nsevent, event, filter->data);
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
       if (result !=  GDK_FILTER_CONTINUE)
 	return result;
     }
@@ -1165,7 +1186,7 @@ gdk_event_translate (GdkEvent *event,
       /* Apply global filters */
       GdkFilterReturn result;
 
-      result = gdk_event_apply_filters (nsevent, event, _gdk_default_filters);
+      result = gdk_event_apply_filters (nsevent, event, &_gdk_default_filters);
       if (result != GDK_FILTER_CONTINUE)
         {
           return_val = (result == GDK_FILTER_TRANSLATE) ? TRUE : FALSE;
@@ -1206,7 +1227,7 @@ gdk_event_translate (GdkEvent *event,
 	{
 	  g_object_ref (window);
 
-	  result = gdk_event_apply_filters (nsevent, event, filter_private->filters);
+	  result = gdk_event_apply_filters (nsevent, event, &filter_private->filters);
 
 	  g_object_unref (window);
 

gdk/win32/gdkevents-win32.c

@@ -1025,7 +1025,7 @@ fill_key_event_string (GdkEvent *event)
 static GdkFilterReturn
 apply_event_filters (GdkWindow  *window,
 		     MSG        *msg,
-		     GList      *filters)
+		     GList     **filters)
 {
   GdkFilterReturn result = GDK_FILTER_CONTINUE;
   GdkEvent *event;
@@ -1043,13 +1043,34 @@ apply_event_filters (GdkWindow  *window,
    */
   node = _gdk_event_queue_append (_gdk_display, event);
   
-  tmp_list = filters;
+  tmp_list = *filters;
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter *) tmp_list->data;
-      
-      tmp_list = tmp_list->next;
+      GList *node;
+
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (msg, event, filter->data);
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
       if (result !=  GDK_FILTER_CONTINUE)
 	break;
     }
@@ -1756,7 +1777,7 @@ gdk_event_translate (MSG  *msg,
     {
       /* Apply global filters */
 
-      GdkFilterReturn result = apply_event_filters (NULL, msg, _gdk_default_filters);
+      GdkFilterReturn result = apply_event_filters (NULL, msg, &_gdk_default_filters);
       
       /* If result is GDK_FILTER_CONTINUE, we continue as if nothing
        * happened. If it is GDK_FILTER_REMOVE or GDK_FILTER_TRANSLATE,
@@ -1822,7 +1843,7 @@ gdk_event_translate (MSG  *msg,
     {
       /* Apply per-window filters */
 
-      GdkFilterReturn result = apply_event_filters (window, msg, ((GdkWindowObject *) window)->filters);
+      GdkFilterReturn result = apply_event_filters (window, msg, &((GdkWindowObject *) window)->filters);
 
       if (result == GDK_FILTER_REMOVE || result == GDK_FILTER_TRANSLATE)
 	{

gdk/x11/gdkeventsource.c

@@ -57,20 +57,40 @@ static GList *event_sources = NULL;
 static gint
 gdk_event_apply_filters (XEvent   *xevent,
 			 GdkEvent *event,
-			 GList    *filters)
+			 GList   **filters)
 {
   GList *tmp_list;
   GdkFilterReturn result;
 
-  tmp_list = filters;
+  tmp_list = *filters;
 
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter*) tmp_list->data;
+      GList *node;
 
-      tmp_list = tmp_list->next;
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (xevent, event, filter->data);
 
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
       if (result != GDK_FILTER_CONTINUE)
 	return result;
     }
@@ -143,7 +163,7 @@ gdk_event_source_translate_event (GdkEventSource *event_source,
       /* Apply global filters */
 
       result = gdk_event_apply_filters (xevent, event,
-                                        _gdk_default_filters);
+                                        &_gdk_default_filters);
 
       if (result == GDK_FILTER_REMOVE)
         {
@@ -167,7 +187,7 @@ gdk_event_source_translate_event (GdkEventSource *event_source,
       if (filter_private->filters)
 	{
 	  result = gdk_event_apply_filters (xevent, event,
-					    filter_private->filters);
+					    &filter_private->filters);
 
           if (result == GDK_FILTER_REMOVE)
             {