Regularly poll the X11 event queue.

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/extensions/XInput2.h>
 #include <X11/X.h>
 #include <X11/Xlib.h>
 #include <X11/XKBlib.h>
 
+#include "base/command_line.h"
 #include "base/logging.h"
 #include "ui/events/devices/x11/device_data_manager_x11.h"
+#include "ui/events/event_switches.h"
 #include "ui/events/event_utils.h"
 #include "ui/events/platform/platform_event_dispatcher.h"
 #include "ui/events/platform/x11/x11_hotplug_event_handler.h"
 #include "ui/gfx/x/x11_types.h"
 
 namespace ui {
 
 namespace {
 
 int g_xinput_opcode = -1;
@@ skipping 50 matching lines @@
 
 }  // namespace
 
 X11EventSource::X11EventSource(XDisplay* display)
     : display_(display),
       continue_stream_(true) {
   CHECK(display_);
   DeviceDataManagerX11::CreateInstance();
   InitializeXInput2(display_);
   InitializeXkb(display_);
+
+  base::CommandLine* cmdline = base::CommandLine::ForCurrentProcess();
+  dispatch_one_event_per_loop_ =
+      cmdline->HasSwitch(switches::kDispatchOneEventPerLoop);
 }
 
 X11EventSource::~X11EventSource() {
 }
 
 // static
 X11EventSource* X11EventSource::GetInstance() {
   return static_cast<X11EventSource*>(PlatformEventSource::GetInstance());
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // X11EventSource, public
 
-void X11EventSource::DispatchXEvents() {
+bool X11EventSource::DispatchXEvents() {
   DCHECK(display_);
-  // Handle all pending events.
-  // It may be useful to eventually align this event dispatch with vsync, but
-  // not yet.
-  continue_stream_ = true;
-  while (XPending(display_) && continue_stream_) {
+
+  int pending_events = XPending(display_);
+  if (!pending_events)
+    return false;
+  do {
     XEvent xevent;
     XNextEvent(display_, &xevent);
     DispatchEvent(&xevent);
-  }
+  } while (--pending_events && continue_stream_ &&
+           !dispatch_one_event_per_loop_);
+  return true;
 }
 
 void X11EventSource::BlockUntilWindowMapped(XID window) {
   XEvent event;
   do {
     // Block until there's a message of |event_mask| type on |w|. Then remove
     // it from the queue and stuff it in |event|.
     XWindowEvent(display_, window, StructureNotifyMask, &event);
     DispatchEvent(&event);
   } while (event.type != MapNotify);
@@ skipping 27 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