abci: remove lock protecting calls to the application interface (#7984)

Closes #7073

As part of the 0.36 cycle we've discussed and decided to remove the mutex in tendermint that protects the ABCI application. First, applications should be able to be responsible for their own concurrency control, and can make more fine-grained decisions about concurrent use than tendermint ever could. Second, I've observed in recent weeks as we've been making this change that the mutex wasn't applied particularly consistently in many cases (e.g. multiple "local" connections to the application had multiple locks, etc.) so this will give more consistent experiences across ABCI execution environments, and simplifies the tendermint ABCI handling code.

abci/server/grpc_server.go

@@ -16,10 +16,9 @@ type GRPCServer struct {
 	service.BaseService
 	logger log.Logger
 
-	proto    string
-	addr     string
-	listener net.Listener
-	server   *grpc.Server
+	proto  string
+	addr   string
+	server *grpc.Server
 
 	app types.ABCIApplicationServer
 }
@@ -28,11 +27,10 @@ type GRPCServer struct {
 func NewGRPCServer(logger log.Logger, protoAddr string, app types.ABCIApplicationServer) service.Service {
 	proto, addr := tmnet.ProtocolAndAddress(protoAddr)
 	s := &GRPCServer{
-		logger:   logger,
-		proto:    proto,
-		addr:     addr,
-		listener: nil,
-		app:      app,
+		logger: logger,
+		proto:  proto,
+		addr:   addr,
+		app:    app,
 	}
 	s.BaseService = *service.NewBaseService(logger, "ABCIServer", s)
 	return s
@@ -40,13 +38,11 @@ func NewGRPCServer(logger log.Logger, protoAddr string, app types.ABCIApplicatio
 
 // OnStart starts the gRPC service.
 func (s *GRPCServer) OnStart(ctx context.Context) error {
-
 	ln, err := net.Listen(s.proto, s.addr)
 	if err != nil {
 		return err
 	}
 
-	s.listener = ln
 	s.server = grpc.NewServer()
 	types.RegisterABCIApplicationServer(s.server, s.app)
 
@@ -57,7 +53,7 @@ func (s *GRPCServer) OnStart(ctx context.Context) error {
 			s.server.GracefulStop()
 		}()
 
-		if err := s.server.Serve(s.listener); err != nil {
+		if err := s.server.Serve(ln); err != nil {
 			s.logger.Error("error serving gRPC server", "err", err)
 		}
 	}()
@@ -65,6 +61,4 @@ func (s *GRPCServer) OnStart(ctx context.Context) error {
 }
 
 // OnStop stops the gRPC server.
-func (s *GRPCServer) OnStop() {
-	s.server.Stop()
-}
+func (s *GRPCServer) OnStop() { s.server.Stop() }