Add concurrent & singleton sample

Author: beyondyyh

grammar/concurrent/main.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+// 生产者：生成 factor 整数倍的序列
+func producer(factor int, out chan<- int) {
+	for i := 0; ; i++ {
+		out <- i * factor
+	}
+}
+
+// 消费者
+func consumer(in <-chan int) {
+	for v := range in {
+		fmt.Println(v)
+	}
+}
+
+func main() {
+	ch := make(chan int, 64)
+
+	go producer(3, ch)
+	// go producer(5, ch)
+	go producer(7, ch)
+	go consumer(ch)
+
+	time.Sleep(500 * time.Millisecond)
+
+	// // Ctrl+C 退出
+	// sig := make(chan os.Signal, 1)
+	// signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
+	// fmt.Printf("quit (%v)\n", <-sig)
+}

grammar/singleton/singleton_by_atomic.go

@@ -0,0 +1,33 @@
+package singleton
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type singleton struct{}
+
+var (
+	instance    *singleton
+	initialized uint32
+	mu          sync.Mutex
+)
+
+// 原子操作`atomic`配合互斥锁`mutex`可以实现非常高效的单件模式
+// 增加一个原子标记位`atomic.StoreUint32(addr *uint32, val uint32)`，
+// 通过原子检测标记位状态`atomic.LoadUint32(addr *unit32)`
+func Instance() *singleton {
+	if atomic.LoadUint32(&initialized) == 1 {
+		return instance
+	}
+
+	mu.Lock()
+	defer mu.Unlock()
+
+	if instance == nil {
+		defer atomic.StoreUint32(&initialized, 1)
+		instance = &singleton{}
+	}
+
+	return instance
+}

grammar/singleton/singleton_by_once.go

@@ -0,0 +1,18 @@
+package singleton
+
+import (
+	"sync"
+)
+
+var (
+	// singleton *singleton
+	once sync.Once
+)
+
+func Instance2() *singleton {
+	once.Do(func() {
+		instance = &singleton{}
+	})
+
+	return instance
+}