Ozone: Avoid blocking in Swapbuffer Call.

ui/ozone/platform/dri/hardware_display_controller.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/hardware_display_controller.h"
 
 #include <drm.h>
 #include <errno.h>
 #include <string.h>
 #include <xf86drm.h>
@@ skipping 84 matching lines @@
   pending_planes_.push_back(plane);
 }
 
 bool HardwareDisplayController::SchedulePageFlip() {
   DCHECK(!pending_planes_.empty());
 
   if (is_disabled_)
     return true;
 
   bool status = true;
-  for (size_t i = 0; i < crtc_controllers_.size(); ++i)
+  for (size_t i = 0; i < crtc_controllers_.size(); ++i) {
     status &= crtc_controllers_[i]->SchedulePageFlip(pending_planes_);
+  }
+
+  current_planes_.swap(pending_planes_);
+  pending_planes_.clear();
 
   return status;
 }
 
 void HardwareDisplayController::WaitForPageFlipEvent() {
   TRACE_EVENT0("dri", "HDC::WaitForPageFlipEvent");
-
   drmEventContext drm_event;
   drm_event.version = DRM_EVENT_CONTEXT_VERSION;
   drm_event.page_flip_handler = HandlePageFlipEvent;
   drm_event.vblank_handler = NULL;
 
-  bool has_pending_page_flips = false;
   // Wait for the page-flips to complete.
   for (size_t i = 0; i < crtc_controllers_.size(); ++i) {
     // In mirror mode the page flip callbacks can happen in different order than
     // scheduled, so we need to make sure that the event for the current CRTC is
     // processed before moving to the next CRTC.
     while (crtc_controllers_[i]->page_flip_pending()) {
-      has_pending_page_flips = true;
       crtc_controllers_[i]->drm()->HandleEvent(drm_event);
     }
   }
-
-  // In case there are no pending pageflips do not replace the current planes
-  // since they are still being used.
-  if (has_pending_page_flips)
-    current_planes_.swap(pending_planes_);
-
-  pending_planes_.clear();
 }
 
 bool HardwareDisplayController::SetCursor(
     const scoped_refptr<ScanoutBuffer>& buffer) {
   bool status = true;
 
   if (is_disabled_)
     return true;
 
   for (size_t i = 0; i < crtc_controllers_.size(); ++i)
@@ skipping 62 matching lines @@
 uint64_t HardwareDisplayController::GetTimeOfLastFlip() const {
   uint64_t time = 0;
   for (size_t i = 0; i < crtc_controllers_.size(); ++i)
     if (time < crtc_controllers_[i]->time_of_last_flip())
       time = crtc_controllers_[i]->time_of_last_flip();
 
   return time;
 }
 
 }  // namespace ui