Merge pull request #9629 from yang-g/qqq

Add a PreServerStart in global server callbacks

include/grpc++/server.h

@@ -88,6 +88,8 @@ class Server final : public ServerInterface, private GrpcLibraryCodegen {
     virtual void PreSynchronousRequest(ServerContext* context) = 0;
     /// Called after application callback for each synchronous server request
     virtual void PostSynchronousRequest(ServerContext* context) = 0;
+    /// Called before server is started.
+    virtual void PreServerStart(Server* server) {}
   };
   /// Set the global callback object. Can only be called once. Does not take
   /// ownership of callbacks, and expects the pointed to object to be alive

src/cpp/server/server_cc.cc

@@ -478,6 +478,7 @@ int Server::AddListeningPort(const grpc::string& addr,
 
 bool Server::Start(ServerCompletionQueue** cqs, size_t num_cqs) {
   GPR_ASSERT(!started_);
+  global_callbacks_->PreServerStart(this);
   started_ = true;
   grpc_server_start(server_);