[XProto] Switch event queue from a std::list to a base::circular_deque

This is needed as a prerequisite for [1].  It also improves performance
a bit by replacing a node-based data structure with a flat one.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2622521

Change-Id: Ibe2e522f6c131876ed73793305524c25b42ab910
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625784
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844303}

ui/base/x/x11_util.cc

@@ -305,16 +305,14 @@ int CoalescePendingMotionEvents(const x11::Event& x11_event,
 
   conn->ReadResponses();
   if (motion) {
-    for (auto it = conn->events().begin(); it != conn->events().end();) {
-      const auto& next_event = *it;
+    for (auto& next_event : conn->events()) {
       // Discard all but the most recent motion event that targets the same
       // window with unchanged state.
       const auto* next_motion = next_event.As<x11::MotionNotifyEvent>();
       if (next_motion && next_motion->event == motion->event &&
           next_motion->child == motion->child &&
           next_motion->state == motion->state) {
-        *last_event = std::move(*it);
-        it = conn->events().erase(it);
+        *last_event = std::move(next_event);
       } else {
         break;
       }
@@ -324,8 +322,8 @@ int CoalescePendingMotionEvents(const x11::Event& x11_event,
            device->opcode == x11::Input::DeviceEvent::TouchUpdate);
 
     auto* ddmx11 = ui::DeviceDataManagerX11::GetInstance();
-    for (auto it = conn->events().begin(); it != conn->events().end();) {
-      auto* next_device = it->As<x11::Input::DeviceEvent>();
+    for (auto& event : conn->events()) {
+      auto* next_device = event.As<x11::Input::DeviceEvent>();
 
       if (!next_device)
         break;
@@ -336,13 +334,13 @@ int CoalescePendingMotionEvents(const x11::Event& x11_event,
       // always be at least one pending.
       if (!ui::TouchFactory::GetInstance()->ShouldProcessDeviceEvent(
               *next_device)) {
-        it = conn->events().erase(it);
+        event = x11::Event();
         continue;
       }
 
       if (next_device->opcode == device->opcode &&
-          !ddmx11->IsCMTGestureEvent(*it) &&
-          ddmx11->GetScrollClassEventDetail(*it) == SCROLL_TYPE_NO_SCROLL) {
+          !ddmx11->IsCMTGestureEvent(event) &&
+          ddmx11->GetScrollClassEventDetail(event) == SCROLL_TYPE_NO_SCROLL) {
         // Confirm that the motion event is targeted at the same window
         // and that no buttons or modifiers have changed.
         if (device->event == next_device->event &&
@@ -353,12 +351,12 @@ int CoalescePendingMotionEvents(const x11::Event& x11_event,
             device->mods.latched == next_device->mods.latched &&
             device->mods.locked == next_device->mods.locked &&
             device->mods.effective == next_device->mods.effective) {
-          *last_event = std::move(*it);
-          it = conn->events().erase(it);
+          *last_event = std::move(event);
           num_coalesced++;
           continue;
         }
       }
+
       break;
     }
   }

ui/events/platform/x11/x11_event_source.cc

@@ -201,8 +201,9 @@ x11::Time X11EventSource::GetCurrentServerTime() {
   };
 
   auto& events = connection_->events();
-  events.erase(std::remove_if(events.begin(), events.end(), pred),
-               events.end());
+  auto it = std::find_if(events.begin(), events.end(), pred);
+  if (it != events.end())
+    *it = x11::Event();
   return time;
 }
 

ui/gfx/x/connection.cc

@@ -287,6 +287,15 @@ bool Connection::HasNextResponse() {
   return true;
 }
 
+bool Connection::HasNextEvent() {
+  while (!events_.empty()) {
+    if (events_.front().Initialized())
+      return true;
+    events_.pop_front();
+  }
+  return false;
+}
+
 int Connection::GetFd() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   return Ready() ? xcb_get_file_descriptor(XcbConnection()) : -1;
@@ -355,7 +364,7 @@ void Connection::ReadResponses() {
 
 Event Connection::WaitForNextEvent() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  if (!events_.empty()) {
+  if (HasNextEvent()) {
     Event event = std::move(events_.front());
     events_.pop_front();
     return event;
@@ -369,7 +378,7 @@ Event Connection::WaitForNextEvent() {
 
 bool Connection::HasPendingResponses() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  return !events_.empty() || HasNextResponse();
+  return HasNextEvent() || HasNextResponse();
 }
 
 const Connection::VisualInfo* Connection::GetVisualInfoFromId(
@@ -405,7 +414,7 @@ void Connection::DetachFromSequence() {
 bool Connection::Dispatch() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
-  if (HasNextResponse() && !events_.empty()) {
+  if (HasNextResponse() && HasNextEvent()) {
     auto next_response_sequence = first_request_id_;
     auto next_event_sequence = events_.front().sequence();
 
@@ -418,7 +427,7 @@ bool Connection::Dispatch() {
       ProcessNextEvent();
   } else if (HasNextResponse()) {
     ProcessNextResponse();
-  } else if (!events_.empty()) {
+  } else if (HasNextEvent()) {
     ProcessNextEvent();
   } else {
     return false;
@@ -488,7 +497,7 @@ void Connection::InitRootDepthAndVisual() {
 
 void Connection::ProcessNextEvent() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  DCHECK(!events_.empty());
+  DCHECK(HasNextEvent());
 
   Event event = std::move(events_.front());
   events_.pop_front();

ui/gfx/x/connection.h

@@ -5,9 +5,6 @@
 #ifndef UI_GFX_X_CONNECTION_H_
 #define UI_GFX_X_CONNECTION_H_
 
-#include <list>
-#include <queue>
-
 #include "base/callback.h"
 #include "base/component_export.h"
 #include "base/containers/circular_deque.h"
@@ -183,8 +180,10 @@ class COMPONENT_EXPORT(X11) Connection : public XProto,
 
   uint32_t KeycodeToKeysym(KeyCode keycode, uint32_t modifiers) const;
 
-  // Access the event buffer.  Clients can add, delete, or modify events.
-  std::list<Event>& events() {
+  // Access the event buffer.  Clients may modify the queue, including
+  // "deleting" events by setting events[i] = x11::Event(), which will
+  // guarantee all calls to x11::Event::As() will return nullptr.
+  base::circular_deque<Event>& events() {
     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
     return events_;
   }
@@ -268,6 +267,8 @@ class COMPONENT_EXPORT(X11) Connection : public XProto,
 
   bool HasNextResponse();
 
+  bool HasNextEvent();
+
   // Creates a new Request and adds it to the end of the queue.
   // |request_name_for_tracing| must be valid until the response is
   // dispatched; currently the string values are only stored in .rodata, so
@@ -312,7 +313,7 @@ class COMPONENT_EXPORT(X11) Connection : public XProto,
 
   std::unique_ptr<KeyboardState> keyboard_state_;
 
-  std::list<Event> events_;
+  base::circular_deque<Event> events_;
 
   base::ObserverList<EventObserver>::Unchecked event_observers_;
 

ui/gfx/x/event.h

@@ -70,6 +70,8 @@ class COMPONENT_EXPORT(X11) Event {
       *window_ = window;
   }
 
+  bool Initialized() const { return deleter_; }
+
  private:
   friend void ReadEvent(Event* event,
                         Connection* connection,