Change AboutResourceLoader::GetAboutResource to wait for inflight update task.

chrome/browser/chromeos/drive/change_list_loader.cc

 // Copyright (c) 2012 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 "chrome/browser/chromeos/drive/change_list_loader.h"
 
 #include <set>
 
 #include "base/callback.h"
 #include "base/callback_helpers.h"
@@ skipping 191 matching lines @@
     return;
 
   std::vector<base::Closure> tasks;
   tasks.swap(pending_tasks_);
   for (size_t i = 0; i < tasks.size(); ++i)
     tasks[i].Run();
 }
 
 AboutResourceLoader::AboutResourceLoader(JobScheduler* scheduler)
     : scheduler_(scheduler),
+      current_update_task_id_(-1),
       weak_ptr_factory_(this) {
 }
 
 AboutResourceLoader::~AboutResourceLoader() {}
 
 void AboutResourceLoader::GetAboutResource(
     const google_apis::AboutResourceCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(!callback.is_null());
 
+  // If the latest UpdateAboutResource task is still running. Wait for it,
+  if (pending_callbacks_.count(current_update_task_id_)) {
+    pending_callbacks_[current_update_task_id_].push_back(callback);
+    return;
+  }
+
   if (cached_about_resource_) {
     base::MessageLoopProxy::current()->PostTask(
         FROM_HERE,
         base::Bind(
             callback,
             google_apis::HTTP_NO_CONTENT,
             base::Passed(scoped_ptr<google_apis::AboutResource>(
                 new google_apis::AboutResource(*cached_about_resource_)))));
   } else {
     UpdateAboutResource(callback);
   }
 }
 
 void AboutResourceLoader::UpdateAboutResource(
     const google_apis::AboutResourceCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(!callback.is_null());
 
+  ++current_update_task_id_;
+  pending_callbacks_[current_update_task_id_].push_back(callback);
+
   scheduler_->GetAboutResource(
       base::Bind(&AboutResourceLoader::UpdateAboutResourceAfterGetAbout,
                  weak_ptr_factory_.GetWeakPtr(),
-                 callback));
+                 current_update_task_id_));
 }
 
 void AboutResourceLoader::UpdateAboutResourceAfterGetAbout(
-    const google_apis::AboutResourceCallback& callback,
+    int task_id,
     google_apis::GDataErrorCode status,
     scoped_ptr<google_apis::AboutResource> about_resource) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK(!callback.is_null());
   FileError error = GDataToFileError(status);
 
-  if (error == FILE_ERROR_OK) {
-    if (cached_about_resource_ &&
-        cached_about_resource_->largest_change_id() >
-        about_resource->largest_change_id()) {
-      LOG(WARNING) << "Local cached about resource is fresher than server, "
-                   << "local = " << cached_about_resource_->largest_change_id()
-                   << ", server = " << about_resource->largest_change_id();
-    }
+  const std::vector<google_apis::AboutResourceCallback> callbacks =
+      pending_callbacks_[task_id];
+  pending_callbacks_.erase(task_id);
 
-    cached_about_resource_.reset(
-        new google_apis::AboutResource(*about_resource));
+  if (error != FILE_ERROR_OK) {
+    for (size_t i = 0; i < callbacks.size(); ++i)
+      callbacks[i].Run(status, scoped_ptr<google_apis::AboutResource>());
+    return;
   }
 
-  callback.Run(status, about_resource.Pass());
+  // Updates the cache when the resource is successfully obtained.
+  if (cached_about_resource_ &&
+      cached_about_resource_->largest_change_id() >
+      about_resource->largest_change_id()) {
+    LOG(WARNING) << "Local cached about resource is fresher than server, "
+                 << "local = " << cached_about_resource_->largest_change_id()
+                 << ", server = " << about_resource->largest_change_id();
+  }
+  cached_about_resource_.reset(new google_apis::AboutResource(*about_resource));
+
+  for (size_t i = 0; i < callbacks.size(); ++i) {
+    callbacks[i].Run(
+        status,
+        make_scoped_ptr(new google_apis::AboutResource(*about_resource)));
+  }
 }
 
 ChangeListLoader::ChangeListLoader(
     EventLogger* logger,
     base::SequencedTaskRunner* blocking_task_runner,
     ResourceMetadata* resource_metadata,
     JobScheduler* scheduler,
     AboutResourceLoader* about_resource_loader,
     LoaderController* loader_controller)
     : logger_(logger),
@@ skipping 252 matching lines @@
 
   OnChangeListLoadComplete(error);
 
   FOR_EACH_OBSERVER(ChangeListLoaderObserver,
                     observers_,
                     OnLoadFromServerComplete());
 }
 
 }  // namespace internal
 }  // namespace drive