修复container/group在相同的key并发get时，可能会初始化多次的bug (#606)

* 修复container/group在相同的key并发get时，可能会初始化多次的bug

* update unit test case

Co-authored-by: demons <lu.xu@zenjoy.net>

pkg/container/group/group.go

@@ -8,7 +8,7 @@ import "sync"
 // Group is a lazy load container.
 type Group struct {
 	new  func() interface{}
-	objs sync.Map
+	objs map[string]interface{}
 	sync.RWMutex
 }
 
@@ -19,19 +19,29 @@ func NewGroup(new func() interface{}) *Group {
 	}
 	return &Group{
 		new: new,
+		objs: make(map[string]interface{}),
 	}
 }
 
 // Get gets the object by the given key.
 func (g *Group) Get(key string) interface{} {
 	g.RLock()
-	new := g.new
-	g.RUnlock()
-	obj, ok := g.objs.Load(key)
-	if !ok {
-		obj = new()
-		g.objs.Store(key, obj)
+	obj, ok := g.objs[key]
+	if ok {
+		g.RUnlock()
+		return obj
 	}
+	g.RUnlock()
+
+	// double check
+	g.Lock()
+	defer g.Unlock()
+	obj, ok = g.objs[key]
+	if ok {
+		return obj
+	}
+	obj = g.new()
+	g.objs[key] = obj
 	return obj
 }
 
@@ -48,8 +58,7 @@ func (g *Group) Reset(new func() interface{}) {
 
 // Clear deletes all objects.
 func (g *Group) Clear() {
-	g.objs.Range(func(key, value interface{}) bool {
-		g.objs.Delete(key)
-		return true
-	})
+	g.Lock()
+	g.objs = make(map[string]interface{})
+	g.Unlock()
 }

pkg/container/group/group_test.go

@@ -36,10 +36,10 @@ func TestGroupReset(t *testing.T) {
 	})
 
 	length := 0
-	g.objs.Range(func(_, _ interface{}) bool {
+	for _,_ = range g.objs {
 		length++
-		return true
-	})
+	}
+
 	assert.Equal(t, 0, length)
 
 	g.Get("/x/internal/dummy/user")
@@ -52,18 +52,16 @@ func TestGroupClear(t *testing.T) {
 	})
 	g.Get("/x/internal/dummy/user")
 	length := 0
-	g.objs.Range(func(_, _ interface{}) bool {
+	for _,_ = range g.objs {
 		length++
-		return true
-	})
+	}
 	assert.Equal(t, 1, length)
 
 	g.Clear()
 	length = 0
-	g.objs.Range(func(_, _ interface{}) bool {
+	for _,_ = range g.objs {
 		length++
-		return true
-	})
+	}
 	assert.Equal(t, 0, length)
 
 }