Mandoline: Introduce ApplicationConnection::CloseConnection

mojo/application/public/cpp/application_connection.h

 // Copyright 2014 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.
 
 #ifndef MOJO_APPLICATION_PUBLIC_CPP_APPLICATION_CONNECTION_H_
 #define MOJO_APPLICATION_PUBLIC_CPP_APPLICATION_CONNECTION_H_
 
 #include <string>
 
 #include "mojo/application/public/cpp/lib/interface_factory_connector.h"
@@ skipping 22 matching lines @@
 //   connection->AddService<Bar>(&my_foo_and_bar_factory_);
 //
 // The InterfaceFactory must outlive the ApplicationConnection.
 //
 // Additionally you specify a ServiceConnector. If a ServiceConnector has
 // been set and an InterfaceFactory has not been registered for the interface
 // request, than the interface request is sent to the ServiceConnector.
 //
 // Just as with InterfaceFactory, ServiceConnector must outlive
 // ApplicationConnection.
+//
+// An ApplicationConnection's lifetime is managed by an ApplicationImpl. To
+// close a connection, call CloseConnection which will destroy this object.
 class ApplicationConnection {
  public:
   virtual ~ApplicationConnection();

[sky, 2015/06/29 16:56:02]

Can the destructor be made protected to prevent accidental usage? Alternatively
can you make it so deleting the connection closes the connection?

[Fady Samuel, 2015/06/29 20:32:36]

I took the following approach.

1. I made ~ApplicationConnection and ~ServiceRegistry protected.
2. I made CloseConnection to be non-virtual.
3. I introduced a protected pure virtual OnCloseConnection() that is overridden
by ServiceRegistry.
4. I introduced a flag connection_closed_ in ApplicationConnection that becomes
true when CloseConnection is called. This both prevents double deletes and
ensures that only CloseConnection can actually destroy the object.
5. I added a DCHECK in ~ApplicationConnection to verify that the
connection_closed_ flag is set.

 
+  // Closes the connection.
+  virtual void CloseConnection() = 0;
+
   // See class description for details.
   virtual void SetServiceConnector(ServiceConnector* connector) = 0;
 
   // Makes Interface available as a service to the remote application.
   // |factory| will create implementations of Interface on demand.
   template <typename Interface>
   void AddService(InterfaceFactory<Interface>* factory) {
     SetServiceConnectorForName(
         new internal::InterfaceFactoryConnector<Interface>(factory),
         Interface::Name_);
@@ skipping 32 matching lines @@
   virtual ServiceProvider* GetServiceProvider() = 0;
 
  private:
   virtual void SetServiceConnectorForName(ServiceConnector* service_connector,
                                           const std::string& name) = 0;
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_APPLICATION_PUBLIC_CPP_APPLICATION_CONNECTION_H_