Use mojo to connect to BackgroundSyncManager object

content/child/background_sync/background_sync_provider.h

Index: content/child/background_sync/background_sync_provider.h
diff --git a/content/child/background_sync/background_sync_provider.h b/content/child/background_sync/background_sync_provider.h
index 0dc6d6c3a56d2acdad12b756f4369698ad532373..bf5489f42493d774948f76c8b5350363e857abac 100644
--- a/content/child/background_sync/background_sync_provider.h
+++ b/content/child/background_sync/background_sync_provider.h
@@ -8,24 +8,27 @@
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
-#include "content/child/worker_task_runner.h"
 #include "content/common/background_sync_service.mojom.h"
+#include "content/public/child/worker_thread.h"
 #include "third_party/WebKit/public/platform/modules/background_sync/WebSyncProvider.h"
 
-namespace content {
+namespace base {
+class SingleThreadTaskRunner;
+}
 
-class ServiceRegistry;
+namespace content {
 
 // The BackgroundSyncProvider is called by the SyncManager and SyncRegistration
 // objects (and their Periodic counterparts) and communicates with the
-// BackgroundSyncManager object in the browser process. This class is
-// instantiated on the main thread by BlinkPlatformImpl, and its methods can be
-// called directly from the main thread.
-class BackgroundSyncProvider : public blink::WebSyncProvider {
+// BackgroundSyncManager object in the browser process. Each thread will have

[jkarlin, 2015/09/28 20:10:05]

It communicates with the BackgroundSyncManager via the
BackgroundSyncServiceImpl. 

[chasej, 2015/10/08 03:28:53]

Acknowledged.

+// its own instance (e.g. main thread, worker threads), instantiated as needed
+// by BlinkPlatformImpl.  Each instance of the provider will create a separate
+// mojo connection to the BackgroundSyncManager object in the browser process.

[jkarlin, 2015/09/28 20:10:05]

Each instance creates a new mojo connection to a new BackgroundSyncServiceImpl.
The ServiceImpl talks to the BackgroundSyncManager.

[chasej, 2015/10/08 03:28:53]

Comment updated to be more precise about the behaviour.

+class BackgroundSyncProvider : public blink::WebSyncProvider,
+                               public WorkerThread::Observer {
  public:
-  explicit BackgroundSyncProvider(ServiceRegistry* service_registry);
-
-  ~BackgroundSyncProvider() override;
+  static BackgroundSyncProvider* GetThreadInstance(
+      base::SingleThreadTaskRunner* main_thread_task_runner);
 
   // blink::WebSyncProvider implementation
   // TODO(jkarlin) convert int64_t handle_id to int handle_id in all
@@ -66,7 +69,15 @@ class BackgroundSyncProvider : public blink::WebSyncProvider {
       const BackgroundSyncService::DuplicateRegistrationHandleCallback&
           callback);
 
+  // WorkerThread::Observer implementation.
+  void WillStopCurrentWorkerThread() override;

[jkarlin, 2015/09/28 20:12:51]

I see how worker threads get killed, thanks to this override. But how does the
main thread's provider get killed?

[michaeln, 2015/10/02 00:13:08]

For other threadspecific classes like this, the instance for the main thread can
be owned and deleted by the RenderThreadImpl (see IndexedDBDispatcher for
example). In newer classes we usually make a distinction between
GetThreadSpecificInstance() and GetOrCreateThreadSpecificInstance(). The
RenderThreadImpl dtor could test and conditionally delete the main threads
instance. I think we might intentionally leak some of these objects too???

+
  private:
+  explicit BackgroundSyncProvider(
+      const scoped_refptr<base::SingleThreadTaskRunner> main_task_runner);
+
+  ~BackgroundSyncProvider() override;
+
   // Callback handlers
   void RegisterCallback(
       scoped_ptr<blink::WebSyncRegistrationCallbacks> callbacks,
@@ -95,8 +106,8 @@ class BackgroundSyncProvider : public blink::WebSyncProvider {
   // Helper method that returns an initialized BackgroundSyncServicePtr.
   BackgroundSyncServicePtr& GetBackgroundSyncServicePtr();
 
-  ServiceRegistry* service_registry_;
   BackgroundSyncServicePtr background_sync_service_;
+  scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(BackgroundSyncProvider);
 };