From 009cf68312ec166d1523f4863229044a6bf75073 Mon Sep 17 00:00:00 2001
From: Tony Chen <zhihui_chen@foxmail.com>
Date: Wed, 8 Sep 2021 23:23:05 +0800
Subject: [PATCH] feat: add container group (#1452)

* add container group
---
 container/group/example_test.go | 42 +++++++++++++++++++++
 container/group/group.go        | 64 ++++++++++++++++++++++++++++++++
 container/group/group_test.go   | 65 +++++++++++++++++++++++++++++++++
 3 files changed, 171 insertions(+)
 create mode 100644 container/group/example_test.go
 create mode 100644 container/group/group.go
 create mode 100644 container/group/group_test.go

diff --git a/container/group/example_test.go b/container/group/example_test.go
new file mode 100644
index 000000000..dc90f229a
--- /dev/null
+++ b/container/group/example_test.go
@@ -0,0 +1,42 @@
+package group
+
+import "fmt"
+
+type Counter struct {
+	Value int
+}
+
+func (c *Counter) Incr() {
+	c.Value++
+}
+
+func ExampleGroup_Get() {
+	group := NewGroup(func() interface{} {
+		fmt.Println("Only Once")
+		return &Counter{}
+	})
+
+	// Create a new Counter
+	group.Get("pass").(*Counter).Incr()
+
+	// Get the created Counter again.
+	group.Get("pass").(*Counter).Incr()
+	// Output:
+	// Only Once
+}
+
+func ExampleGroup_Reset() {
+	group := NewGroup(func() interface{} {
+		return &Counter{}
+	})
+
+	// Reset the new function and clear all created objects.
+	group.Reset(func() interface{} {
+		fmt.Println("reset")
+		return &Counter{}
+	})
+
+	// Create a new Counter
+	group.Get("pass").(*Counter).Incr()
+	// Output:reset
+}
diff --git a/container/group/group.go b/container/group/group.go
new file mode 100644
index 000000000..bb9d0568f
--- /dev/null
+++ b/container/group/group.go
@@ -0,0 +1,64 @@
+// Package group provides a sample lazy load container.
+// The group only creating a new object not until the object is needed by user.
+// And it will cache all the objects to reduce the creation of object.
+package group
+
+import "sync"
+
+// Group is a lazy load container.
+type Group struct {
+	new  func() interface{}
+	vals map[string]interface{}
+	sync.RWMutex
+}
+
+// NewGroup news a group container.
+func NewGroup(new func() interface{}) *Group {
+	if new == nil {
+		panic("container.group: can't assign a nil to the new function")
+	}
+	return &Group{
+		new:  new,
+		vals: make(map[string]interface{}),
+	}
+}
+
+// Get gets the object by the given key.
+func (g *Group) Get(key string) interface{} {
+	g.RLock()
+	v, ok := g.vals[key]
+	if ok {
+		g.RUnlock()
+		return v
+	}
+	g.RUnlock()
+
+	// slowpath for group don`t have specified key value
+	g.Lock()
+	defer g.Unlock()
+	v, ok = g.vals[key]
+	if ok {
+		return v
+	}
+	v = g.new()
+	g.vals[key] = v
+	return v
+}
+
+// Reset resets the new function and deletes all existing objects.
+func (g *Group) Reset(new func() interface{}) {
+	if new == nil {
+		panic("container.group: can't assign a nil to the new function")
+	}
+	g.Lock()
+	g.new = new
+	g.Unlock()
+	g.Clear()
+}
+
+// Clear deletes all objects.
+func (g *Group) Clear() {
+	g.Lock()
+	g.vals = make(map[string]interface{})
+	g.Unlock()
+}
diff --git a/container/group/group_test.go b/container/group/group_test.go
new file mode 100644
index 000000000..46a7d4ac2
--- /dev/null
+++ b/container/group/group_test.go
@@ -0,0 +1,65 @@
+package group
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGroupGet(t *testing.T) {
+	count := 0
+	g := NewGroup(func() interface{} {
+		count++
+		return count
+	})
+	v := g.Get("key_0")
+	assert.Equal(t, 1, v.(int))
+
+	v = g.Get("key_1")
+	assert.Equal(t, 2, v.(int))
+
+	v = g.Get("key_0")
+	assert.Equal(t, 1, v.(int))
+	assert.Equal(t, 2, count)
+}
+
+func TestGroupReset(t *testing.T) {
+	g := NewGroup(func() interface{} {
+		return 1
+	})
+	g.Get("key")
+	call := false
+	g.Reset(func() interface{} {
+		call = true
+		return 1
+	})
+
+	length := 0
+	for range g.vals {
+		length++
+	}
+
+	assert.Equal(t, 0, length)
+
+	g.Get("key")
+	assert.Equal(t, true, call)
+}
+
+func TestGroupClear(t *testing.T) {
+	g := NewGroup(func() interface{} {
+		return 1
+	})
+	g.Get("key")
+	length := 0
+	for range g.vals {
+		length++
+	}
+	assert.Equal(t, 1, length)
+
+	g.Clear()
+	length = 0
+	for range g.vals {
+		length++
+	}
+	assert.Equal(t, 0, length)
+}