service_manager: More consistent Service lifecycle API

services/service_manager/public/cpp/service.h

Index: services/service_manager/public/cpp/service.h
diff --git a/services/service_manager/public/cpp/service.h b/services/service_manager/public/cpp/service.h
index 250b8abdfb4d7e20c51cf69c2b12555d173ed4e0..02d9e0c740f59ad85c77854f67ee320e9662b547 100644
--- a/services/service_manager/public/cpp/service.h
+++ b/services/service_manager/public/cpp/service.h
@@ -23,11 +23,22 @@ class Service {
   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.
   //
@@ -51,24 +62,23 @@ class Service {
   // 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:
@@ -95,7 +105,11 @@ class ForwardingService : public 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;