Fix login visual hitch on chromebook

chrome/browser/chromeos/login/user_image_loader.cc

Index: chrome/browser/chromeos/login/user_image_loader.cc
diff --git a/chrome/browser/chromeos/login/user_image_loader.cc b/chrome/browser/chromeos/login/user_image_loader.cc
index 89fae745c7470cdf743eb2dede89d70dd382861f..ea599a59ae3aab1b72f86a2139010d54c5db5c33 100644
--- a/chrome/browser/chromeos/login/user_image_loader.cc
+++ b/chrome/browser/chromeos/login/user_image_loader.cc
@@ -9,6 +9,7 @@
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
+#include "base/threading/worker_pool.h"
 #include "chrome/browser/chromeos/login/helper.h"
 #include "chrome/browser/chromeos/login/user_image.h"
 #include "content/public/browser/browser_thread.h"
@@ -21,6 +22,9 @@ using content::BrowserThread;
 
 namespace chromeos {
 
+// static
+const char* UserImageLoader::kUserImageLoaderTokenName = "user-image-loader";
+
 UserImageLoader::ImageInfo::ImageInfo(int size,
                                       const LoadedCallback& loaded_cb)
     : size(size),
@@ -33,6 +37,9 @@ UserImageLoader::ImageInfo::~ImageInfo() {
 UserImageLoader::UserImageLoader(ImageDecoder::ImageCodec image_codec)
     : target_message_loop_(NULL),
       image_codec_(image_codec) {
+  sequence_token_ =
+      BrowserThread::GetBlockingPool()->
+          GetNamedSequenceToken(kUserImageLoaderTokenName);

[Nikita (slow), 2013/01/18 16:40:13]

This does mean that there would no 2 image loading operation at a time.

// No two tasks with the same token will run at the same time.

I think we should not have such restriction. Imagine login screen with 18 users
and each of them with custom image.

[Joao da Silva, 2013/01/18 17:24:58]

AFAICT the ImageDecoder spawns a utility process to decode the image, and
multiple processes can be spawned at the same time. If so then using a
non-sequenced task runner won't make the loading faster, but will complicated
this class because OnImageDecoded() will be invoked concurrently, and mutates
image_info_map_.

[Nikita (slow), 2013/01/18 17:41:45]

My point was that first it will load image using this token sequence_token_.
That means that all images will be loaded one by one.

For user images we'll use single UserImageLoader instance so  I agree that there
would be issues while accessing image_info_map_. It should be lock protected
then.

 }
 
 UserImageLoader::~UserImageLoader() {
@@ -44,14 +51,19 @@ void UserImageLoader::Start(const std::string& filepath,
   target_message_loop_ = MessageLoop::current();
 
   ImageInfo image_info(size, loaded_cb);
-  BrowserThread::PostTask(
-      BrowserThread::FILE, FROM_HERE,
+  scoped_refptr<base::SequencedTaskRunner> task_runner =
+      BrowserThread::GetBlockingPool()->
+          GetSequencedTaskRunnerWithShutdownBehavior(
+              sequence_token_, base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
+  task_runner->PostTask(
+      FROM_HERE,
       base::Bind(&UserImageLoader::LoadImage, this, filepath, image_info));
 }
 
 void UserImageLoader::LoadImage(const std::string& filepath,
                                 const ImageInfo& image_info) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  DCHECK(BrowserThread::GetBlockingPool()->
+      IsRunningSequenceOnCurrentThread(sequence_token_));
 
   std::string image_data;
   file_util::ReadFileToString(FilePath(filepath), &image_data);
@@ -59,12 +71,13 @@ void UserImageLoader::LoadImage(const std::string& filepath,
   scoped_refptr<ImageDecoder> image_decoder =
       new ImageDecoder(this, image_data, image_codec_);
   image_info_map_.insert(std::make_pair(image_decoder.get(), image_info));
-  image_decoder->Start();
+  image_decoder->Start(kUserImageLoaderTokenName);

[Joao da Silva, 2013/01/18 17:24:58]

The current task_runner could be passed instead of the token.

 }
 
 void UserImageLoader::OnImageDecoded(const ImageDecoder* decoder,
                                      const SkBitmap& decoded_image) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  DCHECK(BrowserThread::GetBlockingPool()->
+      IsRunningSequenceOnCurrentThread(sequence_token_));
 
   ImageInfoMap::iterator info_it = image_info_map_.find(decoder);
   if (info_it == image_info_map_.end()) {
@@ -106,7 +119,8 @@ void UserImageLoader::OnImageDecoded(const ImageDecoder* decoder,
 }
 
 void UserImageLoader::OnDecodeImageFailed(const ImageDecoder* decoder) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  DCHECK(BrowserThread::GetBlockingPool()->
+      IsRunningSequenceOnCurrentThread(sequence_token_));
 
   ImageInfoMap::iterator info_it = image_info_map_.find(decoder);
   if (info_it == image_info_map_.end()) {