From 1f23c8a85a61e0be91903bae186df15f73a39bca Mon Sep 17 00:00:00 2001
From: Milos Gajdos <milosgajdos83@gmail.com>
Date: Wed, 25 Sep 2019 01:57:37 +0100
Subject: [PATCH] Emit memory registry event only when it actually happens

---
 registry/memory/memory.go | 87 +++++++++++++++++++++++++--------------
 1 file changed, 56 insertions(+), 31 deletions(-)

diff --git a/registry/memory/memory.go b/registry/memory/memory.go
index 6c03df67..446aa0f0 100644
--- a/registry/memory/memory.go
+++ b/registry/memory/memory.go
@@ -10,6 +10,10 @@ import (
 	"github.com/micro/go-micro/registry"
 )
 
+var (
+	timeout = time.Millisecond * 10
+)
+
 type Registry struct {
 	options registry.Options
 
@@ -18,11 +22,28 @@ type Registry struct {
 	Watchers map[string]*Watcher
 }
 
-var (
-	timeout = time.Millisecond * 10
-)
+func NewRegistry(opts ...registry.Option) registry.Registry {
+	options := registry.Options{
+		Context: context.Background(),
+	}
 
-func (m *Registry) watch(r *registry.Result) {
+	for _, o := range opts {
+		o(&options)
+	}
+
+	services := getServices(options.Context)
+	if services == nil {
+		services = make(map[string][]*registry.Service)
+	}
+
+	return &Registry{
+		options:  options,
+		Services: services,
+		Watchers: make(map[string]*Watcher),
+	}
+}
+
+func (m *Registry) sendEvent(r *registry.Result) {
 	var watchers []*Watcher
 
 	m.RLock()
@@ -87,30 +108,55 @@ func (m *Registry) ListServices() ([]*registry.Service, error) {
 }
 
 func (m *Registry) Register(s *registry.Service, opts ...registry.RegisterOption) error {
-	go m.watch(&registry.Result{Action: "update", Service: s})
 	m.Lock()
+	defer m.Unlock()
+
 	if service, ok := m.Services[s.Name]; !ok {
 		m.Services[s.Name] = []*registry.Service{s}
+		go m.sendEvent(&registry.Result{Action: "update", Service: s})
 	} else {
-		m.Services[s.Name] = registry.Merge(service, []*registry.Service{s})
+		svcCount := len(service)
+		svcNodeCounts := make(map[string]map[string]int)
+		for _, s := range service {
+			if _, ok := svcNodeCounts[s.Name]; !ok {
+				svcNodeCounts[s.Name] = make(map[string]int)
+			}
+			if _, ok := svcNodeCounts[s.Name][s.Version]; !ok {
+				svcNodeCounts[s.Name][s.Version] = len(s.Nodes)
+			}
+		}
+		// if merged count and original service counts changed we added new version of the service
+		merged := registry.Merge(service, []*registry.Service{s})
+		if len(merged) != svcCount {
+			m.Services[s.Name] = merged
+			go m.sendEvent(&registry.Result{Action: "update", Service: s})
+			return nil
+		}
+		// if the node count for a particular service has changed we added a new node to the service
+		for _, s := range merged {
+			if len(s.Nodes) != svcNodeCounts[s.Name][s.Version] {
+				m.Services[s.Name] = merged
+				go m.sendEvent(&registry.Result{Action: "update", Service: s})
+				return nil
+			}
+		}
 	}
-	m.Unlock()
 
 	return nil
 }
 
 func (m *Registry) Deregister(s *registry.Service) error {
-	go m.watch(&registry.Result{Action: "delete", Service: s})
-
 	m.Lock()
+	defer m.Unlock()
+
 	if service, ok := m.Services[s.Name]; ok {
+		go m.sendEvent(&registry.Result{Action: "delete", Service: s})
 		if service := registry.Remove(service, []*registry.Service{s}); len(service) == 0 {
 			delete(m.Services, s.Name)
 		} else {
 			m.Services[s.Name] = service
 		}
 	}
-	m.Unlock()
 
 	return nil
 }
@@ -137,24 +183,3 @@ func (m *Registry) Watch(opts ...registry.WatchOption) (registry.Watcher, error)
 func (m *Registry) String() string {
 	return "memory"
 }
-
-func NewRegistry(opts ...registry.Option) registry.Registry {
-	options := registry.Options{
-		Context: context.Background(),
-	}
-
-	for _, o := range opts {
-		o(&options)
-	}
-
-	services := getServices(options.Context)
-	if services == nil {
-		services = make(map[string][]*registry.Service)
-	}
-
-	return &Registry{
-		options:  options,
-		Services: services,
-		Watchers: make(map[string]*Watcher),
-	}
-}