service_manager: More consistent Service lifecycle API

services/service_manager/public/cpp/service.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 SERVICES_SERVICE_MANAGER_PUBLIC_CPP_SERVICE_H_
 #define SERVICES_SERVICE_MANAGER_PUBLIC_CPP_SERVICE_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "mojo/public/cpp/system/message_pipe.h"
 
 namespace service_manager {
 
 class InterfaceRegistry;
 class ServiceContext;
 struct ServiceInfo;
 
 // The primary contract between a Service and the Service Manager, receiving
 // lifecycle notifications and connection requests.
 class Service {
  public:
   Service();
   virtual ~Service();
 
-  // Called exactly once, when a bidirectional connection with the Service
-  // Manager has been established. No calls to OnConnect() will be received
-  // before this.
+  // Called exactly once when a bidirectional connection with the Service
+  // Manager has been established. No calls to OnConnect(), OnBindInterface(),
+  // or OnStop() will be made before this. Note that this call is mutually
+  // exclusive to OnStartFailed() - either one or the other will be the first
+  // call on any given Service instance.
   virtual void OnStart();
 
+  // Called if the Service loses its connection to the Service Manager before
+  // OnStart() could be invoked. Once this called, none of the other public
+  // Service interface methods will be called.  Note that this call is mutually
+  // exclusive to OnStart() - either one or the other will be the first call on
+  // any given Service instance.
+  //
+  // The default implementation calls QuitNow() on context().
+  virtual void OnStartFailed();
+
   // Called each time a connection to this service is brokered by the Service
   // Manager. Implement this to expose interfaces to other services.
   //
   // Return true if the connection should succeed or false if the connection
   // should be rejected.
   //
   // The default implementation returns false.
   virtual bool OnConnect(const ServiceInfo& remote_info,
                          InterfaceRegistry* registry);
 
   // Called when the service identified by |source_info| requests this service
   // bind a request for |interface_name|. If this method has been called, the
   // service manager has already determined that policy permits this interface
   // to be bound, so the implementation of this method can trust that it should
   // just blindly bind it under most conditions.
   virtual void OnBindInterface(const ServiceInfo& source_info,
                                const std::string& interface_name,
                                mojo::ScopedMessagePipeHandle interface_pipe);
 
   // Called when the Service Manager has stopped tracking this instance. The
   // service should use this as a signal to shut down, and in fact its process
   // may be reaped shortly afterward if applicable.
   //
-  // Return true from this method to tell the ServiceContext to signal its
-  // shutdown externally (i.e. to invoke its "connection lost" closure if set),
-  // or return false to defer the signal. If deferred, the Service should
-  // explicitly call QuitNow() on the ServiceContext when it's ready to be
-  // torn down.
+  // Returning true from this method signals that the Service instance can be
+  // destroyed immediately. More precisely, it will cause the context()'s
+  // QuitNow() method to be invoked immediately after this OnStop() call.
+  //
+  // If shutdown is deferred by returning false, the Service itself is
+  // responsible for explicitly calling QuitNow() on context() when it's ready
+  // to be destroyed.
   //
   // The default implementation returns true.
   //
-  // While it's possible for this to be invoked before either OnStart() or
-  // OnConnect() is invoked, neither will be invoked at any point after this
-  // OnStop().
+  // NOTE: This will only be called after OnStart(), and none of the other
+  // public Service methods will be called after this.
   virtual bool OnStop();
 
  protected:
-  // Access the ServiceContext associated with this Service. Note that this is
-  // only valid to call during or after OnStart(), but never before! As such,
-  // it's always safe to call in OnStart() and OnConnect(), but should generally
-  // be avoided in OnStop().
+  // Accesses the ServiceContext associated with this Service. Note that this is
+  // only valid during or after OnStart() or OnStartFailed(), but never before.
   ServiceContext* context() const;
 
  private:
   friend class ForwardingService;
   friend class ServiceContext;
 
   // NOTE: This is guaranteed to be called before OnStart().
   void set_context(ServiceContext* context) { service_context_ = context; }
 
   ServiceContext* service_context_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(Service);
 };
 
 // TODO(rockot): Remove this. It's here to satisfy a few remaining use cases
 // where a Service impl is owned by something other than its ServiceContext.
 class ForwardingService : public Service {
  public:
   // |target| must outlive this object.
   explicit ForwardingService(Service* target);
   ~ForwardingService() override;
 
   // Service:
   void OnStart() override;
   bool OnConnect(const ServiceInfo& remote_info,
                  InterfaceRegistry* registry) override;
+  void OnBindInterface(const ServiceInfo& remote_info,
+                       const std::string& interface_name,
+                       mojo::ScopedMessagePipeHandle interface_pipe) override;
   bool OnStop() override;
+  void OnStartFailed() override;
 
  private:
   Service* const target_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(ForwardingService);
 };
 
 }  // namespace service_manager
 
 #endif  // SERVICES_SERVICE_MANAGER_PUBLIC_CPP_SERVICE_H_