Asynchronously load wallpapers when user pod is selected.

ash/desktop_background/desktop_background_controller.cc

Index: ash/desktop_background/desktop_background_controller.cc
diff --git a/ash/desktop_background/desktop_background_controller.cc b/ash/desktop_background/desktop_background_controller.cc
index e34515878cf112433e4ddc325a1a7422ba1eb3a6..f95c32e9391c4da59e398b819e4a4ba03b71ab04 100644
--- a/ash/desktop_background/desktop_background_controller.cc
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -9,7 +9,10 @@
 #include "ash/shell_factory.h"
 #include "ash/shell_window_ids.h"
 #include "ash/wm/root_window_layout_manager.h"
+#include "base/bind.h"
 #include "base/logging.h"
+#include "base/synchronization/cancellation_flag.h"
+#include "base/threading/worker_pool.h"
 #include "grit/ui_resources.h"
 #include "ui/aura/window.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -19,26 +22,109 @@
 
 namespace ash {
 
-DesktopBackgroundController::DesktopBackgroundController() :
-  desktop_background_mode_(BACKGROUND_IMAGE) {
+// DesktopBackgroundController::WallpaperOperation wraps background wallpaper
+// loading.
+class DesktopBackgroundController::WallpaperOperation
+    : public base::RefCountedThreadSafe<
+    DesktopBackgroundController::WallpaperOperation> {
+ public:
+  WallpaperOperation(int index)
+      : wallpaper_(NULL),
+        layout_(CENTER_CROPPED),
+        index_(index) {
+  }
+
+  static void Run(scoped_refptr<WallpaperOperation> wo) {
+    wo->LoadingWallpaper();
+  }
+
+  void LoadingWallpaper() {
+    if (cancel_flag_.IsSet())
+      return;
+
+    wallpaper_ = ui::ResourceBundle::GetSharedInstance().GetImageNamed(
+      GetWallpaperInfo(index_).id).ToSkBitmap();
+
+    if (cancel_flag_.IsSet())
+      return;
+    layout_ = GetWallpaperInfo(index_).layout;
+  }
+
+  void Cancel() {
+    cancel_flag_.Set();
+  }
+
+  const SkBitmap* wallpaper() {
+    return wallpaper_;
+  }
+
+  ImageLayout image_layout() {
+    return layout_;
+  }
+
+  int index() {
+    return index_;
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<
+      DesktopBackgroundController::WallpaperOperation>;
+  ~WallpaperOperation(){};
+
+  base::CancellationFlag cancel_flag_;
+
+  const SkBitmap* wallpaper_;
+  ImageLayout layout_;
+  int index_;
+
+  DISALLOW_COPY_AND_ASSIGN(WallpaperOperation);
+};
+
+DesktopBackgroundController::DesktopBackgroundController()
+    : desktop_background_mode_(BACKGROUND_IMAGE),
+      previous_index_(-1),
+      weak_ptr_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
 }
 
 DesktopBackgroundController::~DesktopBackgroundController() {
+  CancelPendingWallpaperOperation();
 }
 
-void DesktopBackgroundController::SetDesktopBackgroundImageMode() {
-  internal::RootWindowLayoutManager* root_window_layout =
-      Shell::GetInstance()->root_window_layout();
+void DesktopBackgroundController::SetDefaultWallpaper(int index) {
+  if (previous_index_ == index)
+    return;
+  CancelPendingWallpaperOperation();
+
+  wallpaper_op_ = new WallpaperOperation(index);
+  base::WorkerPool::PostTaskAndReply(
+      FROM_HERE,
+      base::Bind(&WallpaperOperation::Run, wallpaper_op_),
+      base::Bind(&DesktopBackgroundController::OnWallpaperLoadCompleted,
+                 weak_ptr_factory_.GetWeakPtr(),
+                 wallpaper_op_),
+      true /* task_is_slow */);
+}
+
+void DesktopBackgroundController::CancelPendingWallpaperOperation() {
+  // Set canceled flag of previous request to skip unneeded loading.
+  if (wallpaper_op_.get())
+    wallpaper_op_->Cancel();
+
+  // Cancel reply callback for previous request.
+  weak_ptr_factory_.InvalidateWeakPtrs();
+}
+
+void DesktopBackgroundController::SetLoggedInUserWallpaper() {
   int index = Shell::GetInstance()->user_wallpaper_delegate()->
       GetUserWallpaperIndex();
   // We should not change background when index is invalid. For instance, at
-  // login screen.
-  if (index == ash::GetInvalidWallpaperIndex())
+  // login screen or stub_user login.
+  if (index == ash::GetInvalidWallpaperIndex()) {
+    CreateEmptyWallpaper();
     return;
-  root_window_layout->SetBackgroundLayer(NULL);
-  internal::CreateDesktopBackground(GetWallpaper(index),
-                                    GetWallpaperInfo(index).layout);
-  desktop_background_mode_ = BACKGROUND_IMAGE;
+  }
+
+  SetDefaultWallpaper(index);
 }
 
 void DesktopBackgroundController::SetDesktopBackgroundSolidColorMode() {
@@ -56,4 +142,30 @@ void DesktopBackgroundController::SetDesktopBackgroundSolidColorMode() {
   desktop_background_mode_ = BACKGROUND_SOLID_COLOR;
 }
 
+void DesktopBackgroundController::SetDesktopBackgroundImageMode(
+    scoped_refptr<WallpaperOperation> wo) {
+  internal::RootWindowLayoutManager* root_window_layout =
+      Shell::GetInstance()->root_window_layout();
+  root_window_layout->SetBackgroundLayer(NULL);
+  if(wo->wallpaper()) {
+    internal::CreateDesktopBackground(*wo->wallpaper(), wo->image_layout());
+    desktop_background_mode_ = BACKGROUND_IMAGE;
+  }
+}
+
+void DesktopBackgroundController::OnWallpaperLoadCompleted(
+    scoped_refptr<WallpaperOperation> wo) {
+  SetDesktopBackgroundImageMode(wo);
+  previous_index_ = wo->index();
+
+  DCHECK(wo.get() == wallpaper_op_.get());
+  wallpaper_op_ = NULL;
+}
+
+void DesktopBackgroundController::CreateEmptyWallpaper() {
+  SkBitmap dummy;
+  internal::CreateDesktopBackground(dummy, CENTER);
+  desktop_background_mode_ = BACKGROUND_IMAGE;
+}
+
 }  // namespace ash