X11: Avoid round-tripping to get the cursor position

ui/events/platform/x11/x11_event_source.cc

 // Copyright 2014 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.
 
 #include "ui/events/platform/x11/x11_event_source.h"
 
 #include <X11/Xatom.h>
 #include <X11/XKBlib.h>
 #include <X11/Xlib.h>
 
@@ skipping 79 matching lines @@
 
 }  // namespace
 
 X11EventSource* X11EventSource::instance_ = nullptr;
 
 X11EventSource::X11EventSource(X11EventSourceDelegate* delegate,
                                XDisplay* display)
     : delegate_(delegate),
       display_(display),
       event_timestamp_(CurrentTime),
+      dispatching_event_(nullptr),
       dummy_initialized_(false),
       continue_stream_(true) {
   DCHECK(!instance_);
   instance_ = this;
 
   DCHECK(delegate_);
   DCHECK(display_);
   DeviceDataManagerX11::CreateInstance();
   InitializeXkb(display_);
 }
@@ skipping 84 matching lines @@
 ////////////////////////////////////////////////////////////////////////////////
 // X11EventSource, protected
 
 void X11EventSource::ExtractCookieDataDispatchEvent(XEvent* xevent) {
   bool have_cookie = false;
   if (xevent->type == GenericEvent &&
       XGetEventData(xevent->xgeneric.display, &xevent->xcookie)) {
     have_cookie = true;
   }
 
+  dispatching_event_ = xevent;
   event_timestamp_ = ExtractTimeFromXEvent(*xevent);
 
   delegate_->ProcessXEvent(xevent);

[sadrul, 2016/10/07 02:12:51]

This can trigger a nested message loop, which means |dispatching_event_| will
not be reset until the nested message loop ends. So if some code tries to get
the current cursor location (from a timeout task, for example), then it will get
stale information.

[Tom (Use chromium acct), 2016/10/07 21:13:18]

done: added a stack of events to handle this.

   PostDispatchEvent(xevent);
 
   event_timestamp_ = CurrentTime;
+  dispatching_event_ = nullptr;
 
   if (have_cookie)
     XFreeEventData(xevent->xgeneric.display, &xevent->xcookie);
 }
 
 void X11EventSource::PostDispatchEvent(XEvent* xevent) {
   bool should_update_device_list = false;
 
   if (xevent->type == GenericEvent) {
     if (xevent->xgeneric.evtype == XI_HierarchyChanged) {
@@ skipping 40 matching lines @@
 
 void X11EventSource::OnDispatcherListChanged() {
   if (!hotplug_event_handler_) {
     hotplug_event_handler_.reset(new X11HotplugEventHandler());
     // Force the initial device query to have an update list of active devices.
     hotplug_event_handler_->OnHotplugEvent();
   }
 }
 
 }  // namespace ui