Make event-targeting asynchronous in window server.

services/ui/ws/event_targeter.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_UI_WS_EVENT_TARGETER_H_
 #define SERVICES_UI_WS_EVENT_TARGETER_H_
 
 #include <stdint.h>
+#include <queue>
 
+#include "base/callback.h"
 #include "base/macros.h"
-
-namespace gfx {
-class Point;
-}
+#include "base/memory/weak_ptr.h"
+#include "ui/gfx/geometry/point.h"
 
 namespace ui {
-class LocatedEvent;
+class PointerEvent;
 
 namespace ws {
 struct DeepestWindow;
 class EventDispatcherDelegate;
 class ModalWindowController;
 class ServerWindow;
 
 // Keeps track of state associated with an active pointer.
 struct PointerTarget {
   PointerTarget()
       : window(nullptr),
         is_mouse_event(false),
         in_nonclient_area(false),
         is_pointer_down(false) {}
 
   // The target window, which may be null. null is used in two situations:
   // when there is no valid window target, or there was a target but the
   // window is destroyed before a corresponding release/cancel.
   ServerWindow* window;
 
   bool is_mouse_event;
 
   // Did the pointer event start in the non-client area.
   bool in_nonclient_area;
 
   bool is_pointer_down;
 };
 
+using PointerTargetForEventCallback = base::OnceCallback<void(PointerTarget)>;
+using HitTestCallback = base::OnceCallback<void(DeepestWindow)>;
+
 // Finds the PointerTarget for an event or the DeepestWindow for a location.
 class EventTargeter {
  public:
   EventTargeter(EventDispatcherDelegate* event_dispatcher_delegate,
                 ModalWindowController* modal_window_controller);
   ~EventTargeter();
 
-  // Returns a PointerTarget for the supplied |event|. If there is no valid
-  // event target for the specified location |window| in the returned value is
-  // null.
-  PointerTarget PointerTargetForEvent(const ui::LocatedEvent& event,
-                                      int64_t* display_id);
+  // |callback| is called with a PointerTarget for the supplied |event|. If
+  // there is no valid event target for the specified location |window| in the
+  // returned value is null.
+  void PointerTargetForEvent(const ui::PointerEvent& event,
+                             int64_t* display_id,
+                             PointerTargetForEventCallback callback);
 
-  // Returns a DeepestWindow for the supplied |location|. If there is no valid
-  // root window, |window| in the returned value is null.
-  DeepestWindow FindDeepestVisibleWindowForEvents(gfx::Point* location,
-                                                  int64_t* display_id);
+  // Calls WindowFinder to find the deepest visible window for |location|.
+  // |callback| is called with the window found.
+  void FindDeepestVisibleWindowForEvents(gfx::Point* location,
+                                         int64_t* display_id,
+                                         HitTestCallback callback);
+
+  void ProcessNextHittesetRequestFromQueue();
+
+  bool IsHitTestInFlight() const;
 
  private:
+  struct HitTestRequest {
+    HitTestRequest(gfx::Point* location,

[sky, 2017/05/30 17:26:02]

I'm nervous about keeping pointers to members from another class that are
asynchronously processed. That's a recipe for use after free and hard to reason
about. Can these be by value and if needed pass them to the callback?

[riajiang, 2017/05/31 22:44:03]

Makes sense, changed to by value and return the updated location/display_id.

+                   int64_t* display_id,
+                   HitTestCallback hittest_callback);
+    ~HitTestRequest();
+
+    gfx::Point* hittest_location;
+    int64_t* hittest_display_id;
+    HitTestCallback hittest_callback;
+  };
+
+  void PointerTargetForEventOnFoundWindow(const ui::PointerEvent& event,
+                                          DeepestWindow deepest_window);
+
+  void FindDeepestVisibleWindowForEventsImpl(gfx::Point* location,
+                                             int64_t* display_id);
+
+  void FindDeepestVisibleWindowForEventsAsync(gfx::Point* location,
+                                              int64_t* display_id);
+
   EventDispatcherDelegate* event_dispatcher_delegate_;
   ModalWindowController* modal_window_controller_;
 
+  PointerTargetForEventCallback target_callback_;
+
+  std::unique_ptr<gfx::Point> current_hittest_location_;
+  HitTestCallback hittest_callback_;
+
+  // True if we are waiting for the result of a hit-test. False otherwise.
+  bool hittest_in_flight_;
+
+  // Request would go into this queue if it's coming from EventDispatcher::
+  // UpdateNonClientAreaForCurrentWindow() or EventDispatcher::
+  // UpdateCursorProviderByLastKnownLocation(). If it's an event that needs
+  // targeting, it would only go to WindowManagerState::event_queue_ when it's
+  // waiting for an active hit-test.
+  std::queue<std::unique_ptr<HitTestRequest>> hittest_request_queue_;
+
+  base::WeakPtrFactory<EventTargeter> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(EventTargeter);
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_EVENT_TARGETER_H_