Ozone: Avoid blocking in Swapbuffer Call.

ui/ozone/platform/dri/page_flip_event_handler.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/ozone/platform/dri/page_flip_event_handler.h"
+
+#include "base/bind.h"
+#include "ui/ozone/platform/dri/hardware_display_controller.h"
+
+namespace ui {
+
+PageFlipEventHandler::PageFlipEventHandler()
+    : base::Thread("PageFlipEventHandler"),
+      child_message_loop_proxy_(base::MessageLoopProxy::current()) {
+  base::Thread::Options options;
+  options.message_loop_type = base::MessageLoop::TYPE_IO;
+  StartWithOptions(options);
+  SetPriority(base::kThreadPriority_Background);
+}
+
+PageFlipEventHandler::~PageFlipEventHandler() {
+}
+
+void PageFlipEventHandler::GetPageFlipCompleted(
+    HardwareDisplayController* controller,
+    const ui::SurfaceOzoneEGL::PageFlipCompletionCallback& callback) {
+  message_loop_proxy()->PostTask(
+      FROM_HERE, base::Bind(&PageFlipEventHandler::CheckPageFlipEvent, this,
+                            controller, callback));
+}
+
+void PageFlipEventHandler::CleanUp() {
+  SetThreadWasQuitProperly(true);
+}
+
+void PageFlipEventHandler::RunFlipEventCallBack(
+    const ui::SurfaceOzoneEGL::PageFlipCompletionCallback& callback) {
+  callback.Run();
+}
+
+void PageFlipEventHandler::CheckPageFlipEvent(
+    PageFlipEventHandler* data,
+    HardwareDisplayController* controller,
+    const ui::SurfaceOzoneEGL::PageFlipCompletionCallback& callback) {
+  controller->WaitForPageFlipEvent();

[alexst (slow to review), 2014/12/17 19:12:24]

Hi Kalyan, thank you for your help, this is very useful. Danny and I have been
discussing this internally and we think we can do this without introducing an
extra thread here. The gpu io message loop has the ability to watch file
descriptors and notify us when we can read without blocking. This would allow us
to get pageflip events directly from the drm fd asynchronously and dispatch them
to gpu main while avoiding some of the thread safety subtleties.

controller->WaitForPageFlipEvent() for example, is not thread safe and
controller's lifetime is not guaranteed (if a monitor gets unplugged, bad things
could happen here), so this will require addition of locks and subtle
crossthread lifetime management we'd like to avoid.

I like the content/ and ui/gl parts of this patch, let's split them out and land
them separately because they will enable this async behaviour. Meanwhile, we'll
get cranking on the ozone/platform/ part that uses IO thread.

+  data->child_message_loop_proxy_->PostTask(
+      FROM_HERE,
+      base::Bind(&PageFlipEventHandler::RunFlipEventCallBack, callback));
+}
+
+}  // namespace ui