arc-bridge: Expose the Mojo version number of the interfaces

components/arc/arc_bridge_service.h

Index: components/arc/arc_bridge_service.h
diff --git a/components/arc/arc_bridge_service.h b/components/arc/arc_bridge_service.h
index 12aae9d30f76d063bda8a67dfb05e6add5973802..2baa8b9500e72a3521c8da6d49af7b65f321a01f 100644
--- a/components/arc/arc_bridge_service.h
+++ b/components/arc/arc_bridge_service.h
@@ -150,6 +150,13 @@ class ArcBridgeService : public ArcBridgeHost {
   ProcessInstance* process_instance() { return process_ptr_.get(); }
   SettingsInstance* settings_instance() { return settings_ptr_.get(); }
 
+  int32_t app_version() const { return app_ptr_.version(); }
+  int32_t input_version() const { return input_ptr_.version(); }
+  int32_t notifications_version() const { return notifications_ptr_.version(); }
+  int32_t power_version() const { return power_ptr_.version(); }
+  int32_t process_version() const { return process_ptr_.version(); }
+  int32_t settings_version() const { return settings_ptr_.version(); }
+
   // ArcHost:
   void OnAppInstanceReady(AppInstancePtr app_ptr) override;
   void OnInputInstanceReady(InputInstancePtr input_ptr) override;
@@ -184,6 +191,14 @@ class ArcBridgeService : public ArcBridgeHost {
   FRIEND_TEST_ALL_PREFIXES(ArcBridgeTest, Prerequisites);
   FRIEND_TEST_ALL_PREFIXES(ArcBridgeTest, ShutdownMidStartup);
 
+  // Callbacks for QueryVersion.
+  void OnAppVersionReady(int32_t version);
+  void OnInputVersionReady(int32_t version);
+  void OnNotificationsVersionReady(int32_t version);
+  void OnPowerVersionReady(int32_t version);
+  void OnProcessVersionReady(int32_t version);
+  void OnSettingsVersionReady(int32_t version);
+
   // Mojo interfaces.
   AppInstancePtr app_ptr_;
   InputInstancePtr input_ptr_;
@@ -192,6 +207,19 @@ class ArcBridgeService : public ArcBridgeHost {
   ProcessInstancePtr process_ptr_;
   SettingsInstancePtr settings_ptr_;
 
+  // Temporary Mojo interfaces.  After a Mojo interface pointer has been
+  // received from the other endpoint, we still need to asynchronously query
+  // its version.  While that is going on, we should still return nullptr on
+  // the xxx_instance() functions.
+  // To keep the xxx_instance() functions being trivial, store the instance
+  // pointer in a temporary variable to avoid losing its reference.
+  AppInstancePtr temporary_app_ptr_;

[hidehiko, 2015/12/29 13:49:20]

Instead of making temporary_XXX_ptr_ fields, you can pass the ptr to the bound
methods' arguments, I believe.

[Luis Héctor Chávez, 2015/12/29 16:51:09]

That won't work. It would need something like

app_ptr.QueryVersion(base::Bind(...,
                                base::Passed(&app_ptr)));

By the time QueryVersion() is executed, |app_ptr| points to invalid data (or
rather, an empty InterfacePtr<...>), so it crashes on a DCHECK.

Alternatively, passing the InterfacePtr as a pointer, which seems even worse.

[hidehiko, 2016/01/05 08:05:52]

Ah, you're right. QueryVersion is a member of InterfacePtr... Sorry for wrong
suggestion.

+  InputInstancePtr temporary_input_ptr_;
+  NotificationsInstancePtr temporary_notifications_ptr_;
+  PowerInstancePtr temporary_power_ptr_;
+  ProcessInstancePtr temporary_process_ptr_;
+  SettingsInstancePtr temporary_settings_ptr_;
+
   base::ObserverList<Observer> observer_list_;
 
   base::ThreadChecker thread_checker_;
@@ -202,6 +230,9 @@ class ArcBridgeService : public ArcBridgeHost {
   // The current state of the bridge.
   ArcBridgeService::State state_;
 
+  // WeakPtrFactory to use callbacks.
+  base::WeakPtrFactory<ArcBridgeService> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ArcBridgeService);
 };