Make event-targeting asynchronous in window server.

services/ui/ws/event_targeter.cc

Index: services/ui/ws/event_targeter.cc
diff --git a/services/ui/ws/event_targeter.cc b/services/ui/ws/event_targeter.cc
index 1fb3f79e02741cedd283a9456fdb7f32558141e0..531ea8e625acba20bee5e246590625f83447e91b 100644
--- a/services/ui/ws/event_targeter.cc
+++ b/services/ui/ws/event_targeter.cc
@@ -4,18 +4,72 @@
 
 #include "services/ui/ws/event_targeter.h"
 
+#include "base/command_line.h"
+#include "base/memory/ptr_util.h"
+#include "base/task_scheduler/post_task.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "services/ui/ws/event_targeter_delegate.h"
 
 namespace ui {
 namespace ws {
 
+EventTargeter::HitTestRequest::HitTestRequest(const gfx::Point& location,
+                                              int64_t display_id,
+                                              HitTestCallback callback)
+    : location(location),
+      display_id(display_id),
+      callback(std::move(callback)) {}
+
+EventTargeter::HitTestRequest::~HitTestRequest() {}
+
 EventTargeter::EventTargeter(EventTargeterDelegate* event_targeter_delegate)
-    : event_targeter_delegate_(event_targeter_delegate) {}
+    : event_targeter_delegate_(event_targeter_delegate),
+      hit_test_in_flight_(false),
+      weak_ptr_factory_(this) {}
 
 EventTargeter::~EventTargeter() {}
 
-LocationTarget EventTargeter::FindTargetForLocation(const gfx::Point& location,
-                                                    int64_t display_id) {
+void EventTargeter::FindTargetForLocation(const gfx::Point& location,
+                                          int64_t display_id,
+                                          HitTestCallback callback) {
+  if (IsHitTestInFlight()) {
+    std::unique_ptr<HitTestRequest> hittest_request =
+        base::MakeUnique<HitTestRequest>(location, display_id,
+                                         std::move(callback));
+    hit_test_request_queue_.push(std::move(hittest_request));
+    return;
+  }
+
+  ProcessFindTarget(location, display_id, std::move(callback));
+}
+
+bool EventTargeter::IsHitTestInFlight() const {
+  return hit_test_in_flight_ || !hit_test_request_queue_.empty();
+}
+
+void EventTargeter::ProcessFindTarget(const gfx::Point& location,
+                                      int64_t display_id,
+                                      HitTestCallback callback) {
+  // TODO(riajiang): After HitTestComponent is implemented, do synchronous
+  // hit-test for most cases using shared memory and only ask Blink
+  // asynchronously for hard cases. For now, assume all synchronous hit-tests
+  // failed if the "enable-async-event-targeting" flag is turned on.
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          "enable-async-event-targeting")) {
+    DCHECK(!hit_test_in_flight_);
+    hit_test_in_flight_ = true;
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE, base::BindOnce(&EventTargeter::FindTargetForLocationNow,
+                                  weak_ptr_factory_.GetWeakPtr(), location,
+                                  display_id, base::Passed(&callback)));
+  } else {
+    FindTargetForLocationNow(location, display_id, std::move(callback));
+  }
+}
+
+void EventTargeter::FindTargetForLocationNow(const gfx::Point& location,
+                                             int64_t display_id,
+                                             HitTestCallback callback) {
   LocationTarget location_target;
   location_target.location_in_root = location;
   location_target.display_id = display_id;
@@ -26,7 +80,22 @@ LocationTarget EventTargeter::FindTargetForLocation(const gfx::Point& location,
         ui::ws::FindDeepestVisibleWindowForLocation(
             root, location_target.location_in_root);
   }
-  return location_target;
+  std::move(callback).Run(location_target);
+  ProcessNextHitTestRequestFromQueue();
+}
+
+void EventTargeter::ProcessNextHitTestRequestFromQueue() {
+  hit_test_in_flight_ = false;
+  if (hit_test_request_queue_.empty()) {
+    event_targeter_delegate_->ProcessNextAvailableEvent();
+    return;
+  }
+
+  std::unique_ptr<HitTestRequest> hittest_request =
+      std::move(hit_test_request_queue_.front());
+  hit_test_request_queue_.pop();
+  ProcessFindTarget(hittest_request->location, hittest_request->display_id,
+                    std::move(hittest_request->callback));
 }
 
 }  // namespace ws