Disable rendering when suspending on chrome os

ash/system/chromeos/power/power_event_observer.cc

Index: ash/system/chromeos/power/power_event_observer.cc
diff --git a/ash/system/chromeos/power/power_event_observer.cc b/ash/system/chromeos/power/power_event_observer.cc
index 65567f4ed0212ae97e70810a73ca2cb144506225..1510ddd69303de1040aab6c1179f4137fa1c7991 100644
--- a/ash/system/chromeos/power/power_event_observer.cc
+++ b/ash/system/chromeos/power/power_event_observer.cc
@@ -10,13 +10,37 @@
 #include "ash/wm/power_button_controller.h"
 #include "base/prefs/pref_service.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
+#include "ui/aura/window.h"
+#include "ui/aura/window_tree_host.h"
 #include "ui/base/user_activity/user_activity_detector.h"
+#include "ui/compositor/compositor.h"
 #include "ui/display/chromeos/display_configurator.h"
 
 namespace ash {
 
+namespace {
+
+// Tells the compositor for each of the displays to finish all pending
+// rendering requests and block any new ones.
+void StopRenderingRequests() {
+  for (aura::Window* window : Shell::GetAllRootWindows()) {
+    ui::Compositor* compositor = window->GetHost()->compositor();
+    compositor->SetVisible(false);
+    compositor->FinishAllRendering();
+  }
+}
+
+// Tells the compositor for each of the displays to resume sending rendering
+// requests to the GPU.
+void ResumeRenderingRequests() {
+  for (aura::Window* window : Shell::GetAllRootWindows())
+    window->GetHost()->compositor()->SetVisible(true);
+}
+
+}  // namespace
+
 PowerEventObserver::PowerEventObserver()
-    : screen_locked_(false) {
+    : screen_locked_(false), waiting_for_lock_screen_animations_(false) {
   chromeos::DBusThreadManager::Get()->GetPowerManagerClient()->
       AddObserver(this);
   chromeos::DBusThreadManager::Get()->GetSessionManagerClient()->
@@ -30,6 +54,18 @@ PowerEventObserver::~PowerEventObserver() {
       RemoveObserver(this);
 }
 
+void PowerEventObserver::OnLockAnimationsComplete() {
+  VLOG(1) << "Screen locker animations have completed.";
+  waiting_for_lock_screen_animations_ = false;
+
+  if (!screen_lock_callback_.is_null()) {
+    StopRenderingRequests();
+
+    screen_lock_callback_.Run();
+    screen_lock_callback_.Reset();
+  }
+}
+
 void PowerEventObserver::BrightnessChanged(int level, bool user_initiated) {
   Shell::GetInstance()->power_button_controller()->OnScreenBrightnessChanged(
       static_cast<double>(level));
@@ -39,8 +75,19 @@ void PowerEventObserver::SuspendImminent() {
   Shell* shell = Shell::GetInstance();
   SessionStateDelegate* delegate = shell->session_state_delegate();
 
-  // If the lock-before-suspending pref is set, get a callback to block
-  // suspend and ask the session manager to lock the screen.
+  // This class is responsible for disabling all rendering requests at suspend
+  // time and then enabling them at resume time.  When the
+  // lock-before-suspending pref is not set this is easy to do since
+  // StopRenderingRequests() is just called directly from this function.  If the
+  // lock-before-suspending pref _is_ set, then the suspend needs to be delayed
+  // until the lock screen is fully visible.  While it is sufficient from a
+  // security perspective to block only until the lock screen is ready, which
+  // guarantees that the contents of the user's screen are no longer visible,
+  // this leads to poor UX on the first resume since neither the user pod nor
+  // the header bar will be visible for a few hundred milliseconds until the GPU
+  // process starts rendering again.  To deal with this, the suspend is delayed
+  // until all the lock screen animations have completed and the suspend request
+  // is unblocked from OnLockAnimationsComplete().
   if (!screen_locked_ && delegate->ShouldLockScreenBeforeSuspending() &&
       delegate->CanLockScreen()) {
     screen_lock_callback_ = chromeos::DBusThreadManager::Get()->
@@ -48,6 +95,21 @@ void PowerEventObserver::SuspendImminent() {
     VLOG(1) << "Requesting screen lock from PowerEventObserver";
     chromeos::DBusThreadManager::Get()->GetSessionManagerClient()->
         RequestLockScreen();
+  } else if (waiting_for_lock_screen_animations_) {
+    // The lock-before-suspending pref has been set and the lock screen is ready
+    // but the animations have not completed yet.  This can happen if a suspend
+    // request is canceled after the lock screen is ready but before the
+    // animations have completed and then another suspend request is immediately
+    // started.  In practice, it is highly unlikely that this will ever happen
+    // but it's better to be safe since the cost of not dealing with it properly
+    // is a memory leak in the GPU and weird artifacts on the screen.
+    screen_lock_callback_ = chromeos::DBusThreadManager::Get()
+                                ->GetPowerManagerClient()
+                                ->GetSuspendReadinessCallback();
+  } else {
+    // The lock-before-suspending pref is not set or the screen has already been
+    // locked and the animations have completed.  Rendering can be stopped now.
+    StopRenderingRequests();
   }
 
   ui::UserActivityDetector::Get()->OnDisplayPowerChanging();
@@ -57,19 +119,24 @@ void PowerEventObserver::SuspendImminent() {
 void PowerEventObserver::SuspendDone(const base::TimeDelta& sleep_duration) {
   Shell::GetInstance()->display_configurator()->ResumeDisplays();
   Shell::GetInstance()->system_tray_notifier()->NotifyRefreshClock();
+
+  // If the suspend request was being blocked while waiting for the lock
+  // animation to complete, clear the blocker since the suspend has already
+  // completed.  This prevents rendering requests from being blocked after a
+  // resume if the lock screen took too long to show.
+  screen_lock_callback_.Reset();
+
+  ResumeRenderingRequests();
 }
 
 void PowerEventObserver::ScreenIsLocked() {
   screen_locked_ = true;
+  waiting_for_lock_screen_animations_ = true;
 
-  // Stop blocking suspend after the screen is locked.
+  // The screen is now locked but the pending suspend, if any, will be blocked
+  // until all the animations have completed.
   if (!screen_lock_callback_.is_null()) {
     VLOG(1) << "Screen locked due to suspend";
-    // Run the callback asynchronously.  ScreenIsLocked() is currently
-    // called asynchronously after RequestLockScreen(), but this guards
-    // against it being made synchronous later.
-    base::MessageLoop::current()->PostTask(FROM_HERE, screen_lock_callback_);
-    screen_lock_callback_.Reset();
   } else {
     VLOG(1) << "Screen locked without suspend";
   }