From 7af536b2225692a603a97124b2279baea0b4babd Mon Sep 17 00:00:00 2001
From: Edward <chenlulei@gmail.com>
Date: Thu, 23 Apr 2020 09:47:58 +0800
Subject: [PATCH] finish Singleton pattern

---
 creation/03_singleton/README.md         |  8 +++-
 creation/03_singleton/singleton.go      | 47 ++++++++++++++++++----
 creation/03_singleton/singleton_test.go | 52 +++++++++++++++++++------
 3 files changed, 87 insertions(+), 20 deletions(-)

diff --git a/creation/03_singleton/README.md b/creation/03_singleton/README.md
index 8bf5720..6b6ac50 100644
--- a/creation/03_singleton/README.md
+++ b/creation/03_singleton/README.md
@@ -1,3 +1,9 @@
 # 单例模式
 
-使用懒惰模式的单例模式，使用双重检查加锁保证线程安全
+大名鼎鼎的单例模式，永远返回相同内存位置的绝对的、同一个实例对象。
+
+Go有两种常见的单例模式：
+
++ 使用懒惰模式的单例模式，使用`once.Do()`的双重同步检查保证线程安全生成单实例
+
++ 使用初始化的`init(){}`能力保证只生成一个实例
diff --git a/creation/03_singleton/singleton.go b/creation/03_singleton/singleton.go
index c99a380..bd644f1 100644
--- a/creation/03_singleton/singleton.go
+++ b/creation/03_singleton/singleton.go
@@ -2,17 +2,50 @@ package singleton
 
 import "sync"
 
-//Singleton 是单例模式类
-type Singleton struct{}
+////////////////////////////////
+//way 1
+//使用 sync的	once.Do(){}确保执行一次
+////////////////////////////////
 
-var singleton *Singleton
+//Worker Singleton 是单例模式类
+type Worker struct{}
+
+//better to be pointer
+var onlyTheWorker *Worker
+
+// init a control
 var once sync.Once
 
-//GetInstance 用于获取单例模式对象
-func GetInstance() *Singleton {
+//GetWorkerInstance 总是获取到同一个Worker对象(内存位置相同)
+func GetWorkerInstance() *Worker {
+
+	//be sure ,to do this,only once!
 	once.Do(func() {
-		singleton = &Singleton{}
+		onlyTheWorker = &Worker{}
 	})
 
-	return singleton
+	return onlyTheWorker
+}
+
+//Manager Singleton 是单例模式类
+type Manager struct{}
+
+//better to be pointer
+var instance *Manager
+
+//better to be pointer
+var onlyTheManager *Manager
+
+////////////////////////////////
+//way2
+//使用func init(){}函数来初始化保证，只初始化一次,更简单.
+////////////////////////////////
+
+func init() {
+	onlyTheManager = &Manager{}
+}
+
+//GetManagerInstance 总是获取到同一个Manager对象(内存位置相同)
+func GetManagerInstance() *Manager {
+	return onlyTheManager
 }
diff --git a/creation/03_singleton/singleton_test.go b/creation/03_singleton/singleton_test.go
index ad7928e..76dc2b8 100644
--- a/creation/03_singleton/singleton_test.go
+++ b/creation/03_singleton/singleton_test.go
@@ -5,30 +5,58 @@ import (
 	"testing"
 )
 
-const parCount = 100
+const workerCount = 500
 
-func TestSingleton(t *testing.T) {
-	ins1 := GetInstance()
-	ins2 := GetInstance()
+func TestWorkerSingleton(t *testing.T) {
+	ins1 := GetWorkerInstance()
+	ins2 := GetWorkerInstance()
 	if ins1 != ins2 {
-		t.Fatal("instance is not equal")
+		t.Fatal("worker(instance) is not exactly the same")
 	}
 }
 
-func TestParallelSingleton(t *testing.T) {
+// 获取500次，Worker 是否总是同一个worker
+func TestParallelWorkerSingleton(t *testing.T) {
 	wg := sync.WaitGroup{}
-	wg.Add(parCount)
-	instances := [parCount]*Singleton{}
-	for i := 0; i < parCount; i++ {
+	wg.Add(workerCount)
+	instances := [workerCount]*Worker{}
+	for i := 0; i < workerCount; i++ {
 		go func(index int) {
-			instances[index] = GetInstance()
+			instances[index] = GetWorkerInstance()
 			wg.Done()
 		}(i)
 	}
 	wg.Wait()
-	for i := 1; i < parCount; i++ {
+	for i := 1; i < workerCount; i++ {
 		if instances[i] != instances[i-1] {
-			t.Fatal("instance is not equal")
+			t.Fatal("Worker instance is not equal")
+		}
+	}
+}
+
+func TestManagerSingleton(t *testing.T) {
+	ins1 := GetManagerInstance()
+	ins2 := GetManagerInstance()
+	if ins1 != ins2 {
+		t.Fatal("Manager(instance) is not exactly the same")
+	}
+}
+
+// 获取500次，Manager 是否总是同一个Manager
+func TestParallelManagerSingleton(t *testing.T) {
+	wg := sync.WaitGroup{}
+	wg.Add(workerCount)
+	instances := [workerCount]*Manager{}
+	for i := 0; i < workerCount; i++ {
+		go func(index int) {
+			instances[index] = GetManagerInstance()
+			wg.Done()
+		}(i)
+	}
+	wg.Wait()
+	for i := 1; i < workerCount; i++ {
+		if instances[i] != instances[i-1] {
+			t.Fatal("Manager instance is not exactly equal")
 		}
 	}
 }