golang code episode

package main

import (
	"fmt"
	"math/rand"
)

func producer(header string,channel chan<- string)  {
	for  {
		channel<-fmt.Sprintf("%s,%v",header,rand.Int31())
	}
}

func consumer(channel <-chan string)  {
	for  {
		fmt.Println(<-channel)
	}
}

func main()  {
	channel := make(chan string)
	go producer("cat",channel)
	go producer("dog",channel)
	consumer(channel)
}

package main

import (
	"flag"
	"fmt"
)

//定义一个字符串变量，并制定默认值以及使用方式
var species = flag.String("species", "gopher", "the species we are studying")

//定义一个int型字符
var nums  = flag.Int("ins", 1, "ins nums")

func main() {
	// 上面定义了两个简单的参数，在所有参数定义生效前，需要使用flag.Parse()来解析参数
	flag.Parse()
	// 测试上面定义的函数
	fmt.Println("a string flag:",string(*species))
	fmt.Println("ins num:",rune(*nums))
}

//go run flagparse.go -ins 3 -species biaoge

//iota
https://www.cnblogs.com/sunsky303/p/11939873.html

type Stereotype int

const ( 
    TypicalNoob Stereotype = iota // 0 
    TypicalHipster                // 1   TypicalHipster = iota
    TypicalUnixWizard             // 2  TypicalUnixWizard = iota
    TypicalStartupFounder         // 3  TypicalStartupFounder = iota
)
-----------------------------------------------
const a = iota // a=0 
const ( 
  b = iota     //b=0 
  c            //c=1   相当于c=iota
)
-----------------------------------------------
type Allergen int

const ( 
    IgEggs Allergen = 1 << iota         // 1 << 0 which is 00000001 
    IgChocolate                         // 1 << 1 which is 00000010 
    IgNuts                              // 1 << 2 which is 00000100 
    IgStrawberries                      // 1 << 3 which is 00001000 
    IgShellfish                         // 1 << 4 which is 00010000 
)
-----------------------------------------------
type ByteSize float64

const (
    _           = iota                   // ignore first value by assigning to blank identifier
    KB ByteSize = 1 << (10 * iota) // 1 << (10*1)
    MB                                   // 1 << (10*2)
    GB                                   // 1 << (10*3)
    TB                                   // 1 << (10*4)
    PB                                   // 1 << (10*5)
    EB                                   // 1 << (10*6)
    ZB                                   // 1 << (10*7)
    YB                                   // 1 << (10*8)
)
-----------------------------------------------
const (
    Apple, Banana = iota + 1, iota + 2
    Cherimoya, Durian   // = iota + 1, iota + 2 
    Elderberry, Fig     //= iota + 1, iota + 2
)
-----------------------------------------------
const (
Sunday = iota
        Monday
        Tuesday
        Wednesday
        Thursday
        Friday
        Saturday
        numberOfDays // 这个常量没有导出 
)

//文件读取
https://www.jianshu.com/p/1f2c125f8ef3

len,err := fp.Read(sce) //读取小文件
r := bufio.NewReader(fp)  //读取大文件
buff,err := ioutil.Readfile("D:/lnj.txt")//小文件

//文件写入
len,err := os.Write(buf)//一次性写入小文件
w := bufio.NewWriter(fp)//写入较大文件
err := ioutil.WriteFile("D:/lnj.txt", buf, 0666)

encodeString := base64.StdEncoding.EncodeToString(input)
uEnc := base64.URLEncoding.EncodeToString([]byte(input))

package main

import "fmt"

func main() {

	var a int
	var ptr *int
	var pptr **int

	a = 3000

	/* 指针 ptr 地址 */
	ptr = &a

	/* 指向指针 ptr 地址 */
	pptr = &ptr

	/* 获取 pptr 的值 */
	fmt.Printf("变量 a = %d\n", a)
	fmt.Printf("指针变量 *ptr = %d\n", *ptr)
	fmt.Printf("指向指针的指针变量 **pptr = %d\n", **pptr)
	fmt.Println("==================================")
	fmt.Printf("变量的内存地址 a = %d\n", ptr)   //ptr这个值是指向a的内存地址的。
	fmt.Printf("第一个指针变量的内存地址 *ptr = %d\n", pptr)   //pptr这个值，是指向指针ptr在内存中的地址的。
}

// Draw calls DrawMask with a nil mask.
/**
* dst  绘图的背景图。
* r 是背景图的绘图区域
* src 是要绘制的图
* sp 是 src 对应的绘图开始点（绘制的大小 r变量定义了）
* mask 是绘图时用的蒙版，控制替换图片的方式。
* mp 是绘图时蒙版开始点（绘制的大小 r变量定义了）
**/
func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op)
func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point,mask image.Image, mp image.Point, op Op)

/**
* 容器：
* 数组是类型相同的元素的集合, 
* 列表是双链表的容器, 可以添加不同类型的数据
* 切片是对现有数组的引用, 比数组更方便灵活, 还可以追加数据
* 映射是kv键值对
*/

package main

import (
    "container/list"
    "fmt"
)

func main() {
    list1 := [6]int{1,2,3,4}   //数组
    list6 := []string{"a", "b"}//切片
    var list2 [3]int
    // 声明列表, 下面两种为初始化, 生成内存地址, 双链表 ----容器
    var list3 = list.List{}
    list4 := list.New()
    //多维数组
    list5 := [3][2]string{
        {"飞", "小"},
        {"祥", "泰"},
        {"德", "丙"},
    }

    //列表操作
    a1 := list3.PushFront(2) //从左插入
    a2 :=list3.PushBack(1)  //从右插入
    list3.InsertAfter("after", a2)   //在 a2之后
    list3.InsertBefore("before", a1) //在 a1之前
    list3.Remove(a2)
    
    //列表遍历
    for x := list3.Front(); x != nil; x = x.Next() {
        if x.Value == "after" {
            fmt.Println(x.Value)
        }
        fmt.Print(x.Value, " , ")
    }
    //切片遍历
    for _,x := range list1{
        if x == 1{
            fmt.Println(x)
        }
    }
    //切片追加
    list6 = append(list6, "c")
    //也可以和python一样根据索引覆盖值
    list1[5] = 9
    list2[2] = 9
    
    fmt.Println(list1)
    fmt.Println(list2)
    printlist(list3)
    fmt.Println(list4)
    fmt.Println(list5)
    fmt.Println(list6)
}

func printlist(lists list.List)  {
    for x := lists.Front(); x != nil; x = x.Next() {
        fmt.Println(x.Value)
    }
}

	//map 映射
	var scene sync.Map
	// 将键值对保存到sync.Map
	scene.Store("greece", 97)
	scene.Store("london", 100)
	scene.Store("egypt", 200)

	// 从sync.Map中根据键取值
	fmt.Println(scene.Load("london"))

	// 根据键删除对应的键值对
	scene.Delete("london")

	// 遍历所有sync.Map中的键值对
	scene.Range(func(k, v interface{}) bool {

		fmt.Println("iterate:", k, v)
		return true
	})

package main
import "fmt"
func main() {
    //这是我们使用range去求一个slice的和。使用数组跟这个很类似
    nums := []int{2, 3, 4}
    sum := 0
    for _, num := range nums {
        sum += num
    }
    fmt.Println("sum:", sum)
    //在数组上使用range将传入index和值两个变量。上面那个例子我们不需要使用该元素的序号，所以我们使用空白符"_"省略了。有时侯我们确实需要知道它的索引。
    for i, num := range nums {
        if num == 3 {
            fmt.Println("index:", i)
        }
    }
    //range也可以用在map的键值对上。
    kvs := map[string]string{"a": "apple", "b": "banana"}
    for k, v := range kvs {
        fmt.Printf("%s -> %s\n", k, v)
    }
    //range也可以用来枚举Unicode字符串。第一个参数是字符的索引，第二个是字符（Unicode的值）本身。
    for i, c := range "go" {
        fmt.Println(i, c)
    }
}

/*上面例子中的"你好"占据了六个字节

但是其实我们期望得到的结果是8，即不以字节数来计算长度，而是以字符数来计算长度

解决的办法就是将该string转成rune类型，rune类型为int32，即4个字节，能够很好地将utf-8编码下三字节长度的中文字符保存进来，这样就能够得到长度为8的值了
同理可知，其实byte也是为了解决字符的问题，只是它是用来解决ascii字符的，所以长度短一些，为int8
byte 等同于int8，常用来处理ascii字符
rune 等同于int32,常用来处理unicode或utf-8字符
*/
func main() {
	str := "你好 world"
	fmt.Printf("len(str):%d\n", len(str)) //返回len(str):12
	fmt.Printf("len(rune(str)):%d\n", len([]rune(str))) //len(rune(str)):8
}

var a *int
var a []int
var a map[string] int
var a chan int
var a func(string) int
var a error // error 是接口

①：指定变量类型

备注：声明后如不赋值将使用默认值，每个类型都有不同默认值。如int为0，bool为false。

func main() {
　　var num int
　　num = 1
　　fmt.Println(num)
}
 ②：根据赋值自行判定变量

num变量根据赋值内容自动判定该变量类型为int型

func main() {
    var num = 10
    fmt.Println(num)
}
 ③：省略var关键字并赋值

备注：省略var后必须通过":="定义并赋值，否则报错。

func main() {
    num := 10
    fmt.Println(num)
}
 ④：多变量定义

备注：在此过程中发现，定义了的变量必须使用，否则编译报错。

func main() {
    var num1, num2, num3 int = 10, 20, 30
    fmt.Println(num1,num2,num3)
}
 多变量定义由单变量定义大同小异。

⑤：变量不可重复定义

备注：下面代码编译时将会报错，变量一旦定义，变量类型即不可重复定义（相同类型也不可）。

func main() {
    var num1 int = 10
    var num1 string
    fmt.Println(num1,num2,num3)
}
 

//https://blog.youkuaiyun.com/weixin_43586120/article/details/89456183
// 每次外部函数执行的时 候，外部函数的引用地址不同，都会重新创建一个新的地址
func Accumulate(value int) func() int {

	// 返回一个闭包
	return func() int {

		// 累加
		value++

		// 返回一个累加值
		return value
	}
}

//错误转异常，比如程序逻辑上尝试请求某个URL，最多尝试三次，尝试三次的过程中请求失败是错误，尝试完第三次还不成功的话，失败就被提升为异常了。异常转错误，比如panic触发的异常被recover恢复后，将返回值中error类型的变量进行赋值，以便上层函数继续走错误处理流程。

package main

import (
    "fmt"
    "net"
)

func main() {
    addr, err := net.LookupHost("gygolang.com")
    if err, ok := err.(*net.DNSError); ok {
        if err.Timeout() {
            fmt.Println("operation timed out")
        } else if err.Temporary() {
            fmt.Println("temporary error")
        } else {
            fmt.Println("generic error: ", err)
        }
        return
    }
    fmt.Println(addr)
}

package main

import (  
    "fmt"
)

func recoverName() {  
    if r := recover(); r!= nil {
        fmt.Println("recovered from ", r)
    }
}

func fullName(firstName *string, lastName *string) {  
    defer recoverName()
    if firstName == nil {
        panic("runtime error: first name cannot be nil")
    }
    if lastName == nil {
        panic("runtime error: last name cannot be nil")
    }
    fmt.Printf("%s %s\n", *firstName, *lastName)
    fmt.Println("returned normally from fullName")
}

func main() {  
    defer fmt.Println("deferred call in main")
    firstName := "foo"
    fullName(&firstName, nil)
    fmt.Println("returned normally from main")
}

//链式处理，将数据和操作拆分、解耦

// 字符串处理函数，传入字符串切片和处理链
func StringProccess(list []string, chain []func(string) string) {

	// 遍历每一个字符串
	for index, str := range list {

		// 第一个需要处理的字符串
		result := str

		// 遍历每一个处理链
		for _, proc := range chain {

			// 输入一个字符串进行处理，返回数据作为下一个处理链的输入。
			result = proc(result)
		}

		// 将结果放回切片
		list[index] = result
	}
}

// 自定义的移除前缀的处理函数
func removePrefix(str string) string {

	return strings.TrimPrefix(str, "go")
}

func main() {

	// 待处理的字符串列表
	list := []string{
		"go scanner",
		"go parser",
		"go compiler",
		"go printer",
		"go formater",
	}

	// 处理函数链
	chain := []func(string) string{
		removePrefix,
		strings.TrimSpace,
		strings.ToUpper,
	}

	// 处理字符串
	StringProccess(list, chain)

	// 输出处理好的字符串
	for _, str := range list {
		fmt.Println(str)
	}

}

func main() {
   i := 10 //整形变量 i
   ip := &i //指向整型变量 i 的指针ip,包含了 i 的内存地址
   fmt.Printf("main中i的值为：%v，i 的内存地址为：%v，i的指针的内存地址为：%v\n",i,ip,&ip)
   modify(i)
   fmt.Printf("main中i的值为：%v，i 的内存地址为：%v，i的指针的内存地址为：%v\n",i,ip,&ip)
}

func modify(i int) {
   fmt.Printf("modify i 为：%v，i的指针的内存地址为：%v\n",i,&i)
   i = 11
}

----output---- 
main中 i 的值为：10，i 的内存地址为：0xc0420080b8，i 的指针的内存地址为：0xc042004028
modify i 为：10，i 的指针的内存地址为：0xc0420080d8
main中 i 的值为：10，i 的内存地址为：0xc0420080b8，i 的指针的内存地址为：0xc042004028

func main() {
   i := 10 //整形变量 i
   ip := &i //指向整型变量 i 的指针ip,包含了 i 的内存地址
   fmt.Printf("main中i的值为：%v，i 的内存地址为：%v，i的指针的内存地址为：%v\n",i,ip,&ip)
   modifyBypointer(ip)
   fmt.Printf("main中i的值为：%v，i 的内存地址为：%v，i的指针的内存地址为：%v\n",i,ip,&ip)
}

func modifyBypointer(i *int) {
   fmt.Printf("modifyBypointer i 的内存地址为：%v，i的指针的内存地址为：%v\n",i,&i)
   *i = 11
}

---output---
main中i的值为：10，i 的内存地址为：0xc042060080，i的指针ip的内存地址为：0xc042080018
modifyBypointer i 的内存地址为：0xc042060080，i的指针ip的内存地址为：0xc042080028
main中i的值为：11，i 的内存地址为：0xc042060080，i的指针ip的内存地址为：0xc042080018

//函数实现方法
package main

import (
	"fmt"
)

// 调用器接口
type Invoker interface {
	// 需要实现一个Call方法
	Call(interface{})
}

// 结构体类型
type Struct struct {
}

// 实现Invoker的Call
func (s *Struct) Call(p interface{}) {
	fmt.Println("from struct", p)
}

// 函数定义为类型
type FuncCaller func(interface{})

// 实现Invoker的Call
func (f FuncCaller) Call(p interface{}) {

	// 调用f函数本体
	f(p)
}

func main() {

	// 声明接口变量
	var invoker Invoker

	// 实例化结构体
	s := new(Struct)

	// 将实例化的结构体赋值到接口
	invoker = s

	// 使用接口调用实例化结构体的方法Struct.Call
	invoker.Call("hello")

	// 将匿名函数转为FuncCaller类型，再赋值给接口
	invoker = FuncCaller(func(v interface{}) {
		fmt.Println("from function", v)
	})

	// 使用接口调用FuncCaller.Call，内部会调用函数本体
	invoker.Call("hello")
}

package main
import "fmt"

type Rect struct{
	width float64
	height float64
}

func(r *Rect) size() float64{
	return r.width * r.height
}

func main()  {
	//fmt.Println(&Rect{100,100})

	//var r *Rect = &Rect{100,100}
	//fmt.Println(r)

	var r *Rect = &Rect{100,100}
	fmt.Println(*r)
}

package main

import "fmt"

// 可飞行的
type Flying struct{}

func (f *Flying) Fly() {
	fmt.Println("can fly")
}

// 可行走的
type Walkable struct{}

func (f *Walkable) Walk() {
	fmt.Println("can calk")
}

// 人类
type Human struct {
	Walkable // 人类能行走
}

// 鸟类
type Bird struct {
	Walkable // 鸟类能行走
	Flying   // 鸟类能飞行
}

func main() {

	// 实例化鸟类
	b := new(Bird)
	fmt.Println("Bird: ")
	b.Fly()
	b.Walk()

	// 实例化人类
	h := new(Human)
	fmt.Println("Human: ")
	h.Walk()

}

package main

import "fmt"

// 声明一个结构体
type class struct {
}

// 给结构体添加Do方法
func (c *class) Do(v int) {

	fmt.Println("call method do:", v)
}

// 普通函数的Do
func funcDo(v int) {

	fmt.Println("call function do:", v)
}

func main() {

	// 声明一个函数回调
	var delegate func(int)

	// 创建结构体实例
	c := new(class)

	// 将回调设为c的Do方法
	delegate = c.Do

	// 调用
	delegate(100)

	// 将回调设为普通函数
	delegate = funcDo

	// 调用
	delegate(100)
}

package main

import (
	"fmt"
)

// 定义一个数据写入器
type DataWriter interface {
	WriteData(data interface{}) error
}

// 定义文件结构，用于实现DataWriter
type file struct {
}

// 实现DataWriter接口的WriteData方法
func (d *file) WriteData(data interface{}) error {

	// 模拟写入数据
	fmt.Println("WriteData:", data)
	return nil
}

func main() {

	// 实例化file
	f := new(file)

	// 声明一个DataWriter的接口
	var writer DataWriter

	// 将接口赋值f，也就是*file类型
	writer = f

	// 使用DataWriter接口进行数据写入
	writer.WriteData("data234567")
}

		// 计算数据的hash值，取出已经存在的记录
		existValue := mapper[key.hash()]
		fmt.Println(key.hash())
		// 将当前数据添加到已经存在的记录切片中
		existValue = append(existValue, profile)
		fmt.Println(existValue)
		// 将切片重新设置到映射中
		mapper[key.hash()] = existValue

package main

import (
	"fmt"
	"math/rand"
	"sync"
)

func main() {
	var count int
	var once sync.Once
	max := rand.Intn(100)
	for i := 0; i < max; i++ {
		once.Do(func() {
			count++
		})
	}
	fmt.Printf("Count: %d.\n", count)
}

package main

import (
	"fmt"
	"runtime"
	"runtime/debug"
	"sync"
	"sync/atomic"
)

func main() {
	// 禁用GC，并保证在main函数执行结束前恢复GC。
	defer debug.SetGCPercent(debug.SetGCPercent(-1))
	var count int32
	newFunc := func() interface{} {
		return atomic.AddInt32(&count, 1)
	}
	pool := sync.Pool{New: newFunc}

	// New 字段值的作用。
	v1 := pool.Get()
	fmt.Printf("Value 1: %v\n", v1)

	// 临时对象池的存取。
	pool.Put(100)
	pool.Put(110)
	pool.Put(120)
	v2 := pool.Get()
	fmt.Printf("Value 2: %v\n", v2)

	// 垃圾回收对临时对象池的影响。
	debug.SetGCPercent(100)
	runtime.GC()
	v3 := pool.Get()
	fmt.Printf("Value 3: %v\n", v3)
	pool.New = nil
	v4 := pool.Get()
	fmt.Printf("Value 4: %v\n", v4)
}

package main

import (
	"fmt"
	"time"
)

func main() {
	names := []string{"Eric", "Harry", "Robert", "Jim", "Mark"}
	for _, name := range names {
		go func(who string) {
			fmt.Printf("Hello, %s!\n", who)
		}(name)
	}
	time.Sleep(time.Millisecond)
}

package main

import (
	"fmt"
	"time"
)

func main() {
	intChan := make(chan int, 1)
	ticker := time.NewTicker(time.Second)
	go func() {
		for _ = range ticker.C {
			select {
			case intChan <- 1:
			case intChan <- 2:
			case intChan <- 3:
			}
		}
		fmt.Println("End. [sender]")
	}()
	var sum int
	for e := range intChan {
		fmt.Printf("Received: %v\n", e)
		sum += e
		if sum > 10 {
			fmt.Printf("Got: %v\n", sum)
			break
		}
	}
	fmt.Println("End. [receiver]")
}

package main

import (
	"fmt"
	"time"
)

func main() {
	intChan := make(chan int, 1)
	go func() {
		for i := 0; i < 5; i++ {
			time.Sleep(time.Second)
			intChan <- i
		}
		close(intChan)
	}()
	timeout := time.Millisecond * 500
	var timer *time.Timer
	for {
		if timer == nil {
			timer = time.NewTimer(timeout)
		} else {
			timer.Reset(timeout)
		}
		select {
		case e, ok := <-intChan:
			if !ok {
				fmt.Println("End.")
				return
			}
			fmt.Printf("Received: %v\n", e)
		case <-timer.C:
			fmt.Println("Timeout!")
		}
	}

}

package main

import "fmt"

func main() {
	intChan := make(chan int, 10)
	for i := 0; i < 10; i++ {
		intChan <- i
	}
	close(intChan)
	syncChan := make(chan struct{}, 1)
	go func() {
	Loop:
		for {
			select {
			case e, ok := <-intChan:
				if !ok {
					fmt.Println("End.")
					break Loop
				}
				fmt.Printf("Received: %v\n", e)
			}
		}
		syncChan <- struct{}{}
	}()
	<-syncChan
}

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"os/exec"
)

func main() {
	runCmd()
	fmt.Println()
	runCmdWithPipe()
}

func runCmdWithPipe() {
	fmt.Println("Run command `ps aux | grep apipe`: ")
	cmd1 := exec.Command("ps", "aux")
	cmd2 := exec.Command("grep", "apipe")
	var outputBuf1 bytes.Buffer
	cmd1.Stdout = &outputBuf1
	if err := cmd1.Start(); err != nil {
		fmt.Printf("Error: The first command can not be startup %s\n", err)
		return
	}
	if err := cmd1.Wait(); err != nil {
		fmt.Printf("Error: Couldn't wait for the first command: %s\n", err)
		return
	}
	cmd2.Stdin = &outputBuf1
	var outputBuf2 bytes.Buffer
	cmd2.Stdout = &outputBuf2
	if err := cmd2.Start(); err != nil {
		fmt.Printf("Error: The second command can not be startup: %s\n", err)
		return
	}
	if err := cmd2.Wait(); err != nil {
		fmt.Printf("Error: Couldn't wait for the second command: %s\n", err)
		return
	}
	fmt.Printf("%s\n", outputBuf2.Bytes())
}

func runCmd() {
	useBufferedIO := false
	fmt.Println("Run command `echo -n \"My first command comes from golang.\"`: ")
	cmd0 := exec.Command("echo", "-n", "My first command comes from golang.")
	stdout0, err := cmd0.StdoutPipe()
	if err != nil {
		fmt.Printf("Error: Couldn't obtain the stdout pipe for command No.0: %s\n", err)
		return
	}
	defer stdout0.Close()
	if err := cmd0.Start(); err != nil {
		fmt.Printf("Error: The command No.0 can not be startup: %s\n", err)
		return
	}
	if !useBufferedIO {
		var outputBuf0 bytes.Buffer
		for {
			tempOutput := make([]byte, 5)
			n, err := stdout0.Read(tempOutput)
			if err != nil {
				if err == io.EOF {
					break
				} else {
					fmt.Printf("Error: Couldn't read data from the pipe: %s\n", err)
					return
				}
			}
			if n > 0 {
				outputBuf0.Write(tempOutput[:n])
			}
		}
		fmt.Printf("%s\n", outputBuf0.String())
	} else {
		outputBuf0 := bufio.NewReader(stdout0)
		output0, _, err := outputBuf0.ReadLine()
		if err != nil {
			fmt.Printf("Error: Couldn't read data from the pipe: %s\n", err)
			return
		}
		fmt.Printf("%s\n", string(output0))
	}
}

package main

import (
	"fmt"
	"io"
	"os"
	"time"
)

func main() {
	fileBasedPipe()
	inMemorySyncPipe()
}

func fileBasedPipe() {
	reader, writer, err := os.Pipe()
	if err != nil {
		fmt.Printf("Error: Couldn't create the named pipe: %s\n", err)
	}
	go func() {
		output := make([]byte, 100)
		n, err := reader.Read(output)
		if err != nil {
			fmt.Printf("Error: Couldn't read data from the named pipe: %s\n", err)
		}
		fmt.Printf("Read %d byte(s). [file-based pipe]\n", n)
	}()
	input := make([]byte, 26)
	for i := 65; i <= 90; i++ {
		input[i-65] = byte(i)
	}
	n, err := writer.Write(input)
	if err != nil {
		fmt.Printf("Error: Couldn't write data to the named pipe: %s\n", err)
	}
	fmt.Printf("Written %d byte(s). [file-based pipe]\n", n)
	time.Sleep(200 * time.Millisecond)
}

func inMemorySyncPipe() {
	reader, writer := io.Pipe()
	go func() {
		output := make([]byte, 100)
		n, err := reader.Read(output)
		if err != nil {
			fmt.Printf("Error: Couldn't read data from the named pipe: %s\n", err)
		}
		fmt.Printf("Read %d byte(s). [in-memory pipe]\n", n)
	}()
	input := make([]byte, 26)
	for i := 65; i <= 90; i++ {
		input[i-65] = byte(i)
	}
	n, err := writer.Write(input)
	if err != nil {
		fmt.Printf("Error: Couldn't write data to the named pipe: %s\n", err)
	}
	fmt.Printf("Written %d byte(s). [in-memory pipe]\n", n)
	time.Sleep(200 * time.Millisecond)
}

package main

import (
	"fmt"
	"time"
)

// Counter 代表计数器的类型。
type Counter struct {
	count int
}

var mapChan = make(chan map[string]*Counter, 1)

func main() {
	syncChan := make(chan struct{}, 2)
	go func() { // 用于演示接收操作。
		for {
			if elem, ok := <-mapChan; ok {
				counter := elem["count"]
				counter.count++
			} else {
				break
			}
		}
		fmt.Println("Stopped. [receiver]")
		syncChan <- struct{}{}
	}()
	go func() { // 用于演示发送操作。
		countMap := map[string]*Counter{
			"count": &Counter{},
		}
		for i := 0; i < 5; i++ {
			mapChan <- countMap
			time.Sleep(time.Millisecond)
			fmt.Printf("The count map: %v. [sender]\n", countMap)
		}
		close(mapChan)
		syncChan <- struct{}{}
	}()
	<-syncChan
	<-syncChan
}


func (counter *Counter) String() string  {
	return fmt.Sprintf("{count:%d}",counter.count)
}

package main

import (
	"fmt"
	"time"
)

var mapChan = make(chan map[string]int, 1)

func main() {
	syncChan := make(chan struct{}, 2)
	go func() { // 用于演示接收操作。
		for {
			if elem, ok := <-mapChan; ok {
				elem["count"]++
			} else {
				break
			}
		}
		fmt.Println("Stopped. [receiver]")
		syncChan <- struct{}{}
	}()
	go func() { // 用于演示发送操作。
		countMap := make(map[string]int)
		for i := 0; i < 5; i++ {
			mapChan <- countMap
			time.Sleep(time.Millisecond)
			fmt.Printf("The count map: %v. [sender]\n", countMap)
		}
		close(mapChan)
		syncChan <- struct{}{}
	}()
	<-syncChan
	<-syncChan
}

package main

import "fmt"

func main() {
	dataChan := make(chan int, 5)
	syncChan1 := make(chan struct{}, 1)
	syncChan2 := make(chan struct{}, 2)
	go func() { // 用于演示接收操作。
		<-syncChan1
		for {
			if elem, ok := <-dataChan; ok {
				fmt.Printf("Received: %d [receiver]\n", elem)
			} else {
				break
			}
		}
		fmt.Println("Done. [receiver]")
		syncChan2 <- struct{}{}
	}()
	go func() { // 用于演示发送操作。
		for i := 0; i < 5; i++ {
			dataChan <- i
			fmt.Printf("Sent: %d [sender]\n", i)
		}
		close(dataChan)
		syncChan1 <- struct{}{}
		fmt.Println("Done. [sender]")
		syncChan2 <- struct{}{}
	}()
	<-syncChan2
	<-syncChan2
}

package main

import (
	"fmt"
	"time"
)

func main() {
	sendingInterval := time.Second
	receptionInterval := time.Second * 2
	intChan := make(chan int, 0)
	go func() {
		var ts0, ts1 int64
		for i := 1; i <= 5; i++ {
			intChan <- i
			ts1 = time.Now().Unix()
			if ts0 == 0 {
				fmt.Println("Sent:", i)
			} else {
				fmt.Printf("Sent: %d [interval: %d s]\n", i, ts1-ts0)
			}
			ts0 = time.Now().Unix()
			time.Sleep(sendingInterval)
		}
		close(intChan)
	}()
	var ts0, ts1 int64
Loop:
	for {
		select {
		case v, ok := <-intChan:
			if !ok {
				break Loop
			}
			ts1 = time.Now().Unix()
			if ts0 == 0 {
				fmt.Println("Received:", v)
			} else {
				fmt.Printf("Received: %d [interval: %d s]\n", v, ts1-ts0)
			}
		}
		ts0 = time.Now().Unix()
		time.Sleep(receptionInterval)
	}
	fmt.Println("End.")
}

package main

import "fmt"

func main() {
	var ok bool
	ch := make(chan int, 1)
	_, ok = interface{}(ch).(<-chan int)
	fmt.Println("chan int => <-chan int:", ok)
	_, ok = interface{}(ch).(chan<- int)
	fmt.Println("chan int => chan<- iRnt:", ok)

	sch := make(chan<- int, 1)
	_, ok = interface{}(sch).(chan int)
	fmt.Println("chan<- int => chan int:", ok)

	rch := make(<-chan int, 1)
	_, ok = interface{}(rch).(chan int)
	fmt.Println("<-chan int => chan int:", ok)
}

package main

import (
	"fmt"
	"sync/atomic"
)

func main() {
	var countVal atomic.Value
	countVal.Store([]int{1, 3, 5, 7})
	anotherStore(countVal)
	fmt.Printf("The count value: %+v \n", countVal.Load())
}

func anotherStore(countVal atomic.Value) {
	countVal.Store([]int{2, 4, 6, 8})
}

package main

import (
	"fmt"
	"time"
)

var strChan = make(chan string, 3)

func main() {
	syncChan1 := make(chan struct{}, 1)
	syncChan2 := make(chan struct{}, 2)
	go func() { // 用于演示接收操作。
		<-syncChan1
		fmt.Println("Received a sync signal and wait a second... [receiver]")
		time.Sleep(time.Second)
		for {
			if elem, ok := <-strChan; ok {
				fmt.Println("Received:", elem, "[receiver]")
			} else {
				break
			}
		}
		fmt.Println("Stopped. [receiver]")
		syncChan2 <- struct{}{}
	}()
	go func() { // 用于演示发送操作。
		for _, elem := range []string{"a", "b", "c", "d"} {
			strChan <- elem
			fmt.Println("Sent:", elem, "[sender]")
			if elem == "c" {
				syncChan1 <- struct{}{}
				fmt.Println("Sent a sync signal. [sender]")
			}
		}
		fmt.Println("Wait 2 seconds... [sender]")
		time.Sleep(time.Second * 2)
		close(strChan)
		syncChan2 <- struct{}{}
	}()
	<-syncChan2
	<-syncChan2
}

package main

import (
	"fmt"
	"time"
)

var strChan = make(chan string, 3)

func main() {
	syncChan1 := make(chan struct{}, 1)
	syncChan2 := make(chan struct{}, 2)
	go receive(strChan, syncChan1, syncChan2) // 用于演示接收操作。
	go send(strChan, syncChan1, syncChan2)    // 用于演示发送操作。
	<-syncChan2
	<-syncChan2
}

func receive(strChan <-chan string,
	syncChan1 <-chan struct{},
	syncChan2 chan<- struct{}) {å
	<-syncChan1
	fmt.Println("Received a sync signal and wait a second... [receiver]")
	time.Sleep(time.Second)
	for elem := range strChan {
		fmt.Println("Received:", elem, "[receiver]")
	}
	fmt.Println("Stopped. [receiver]")
	syncChan2 <- struct{}{}
}

func send(strChan chan<- string,
	syncChan1 chan<- struct{},
	syncChan2 chan<- struct{}) {
	for _, elem := range []string{"a", "b", "c", "d"} {
		strChan <- elem
		fmt.Println("Sent:", elem, "[sender]")
		if elem == "c" {
			syncChan1 <- struct{}{}
			fmt.Println("Sent a sync signal. [sender]")
		}
	}
	fmt.Println("Wait 2 seconds... [sender]")
	time.Sleep(time.Second * 2)
	close(strChan)
	syncChan2 <- struct{}{}
}

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var mutex sync.Mutex
	fmt.Println("Lock the lock. (main)")
	mutex.Lock()
	fmt.Println("The lock is locked. (main)")
	for i := 1; i <= 3; i++ {
		go func(i int) {
			fmt.Printf("Lock the lock. (g%d)\n", i)
			mutex.Lock()
			fmt.Printf("The lock is locked. (g%d)\n", i)
		}(i)
	}
	time.Sleep(time.Second)
	fmt.Println("Unlock the lock. (main)")
	mutex.Unlock()
	fmt.Println("The lock is unlocked. (main)")
	time.Sleep(time.Second)
}

package main

import (
	"fmt"
	"sync"
)

func main() {
	defer func() {
		fmt.Println("Try to recover the panic.")
		if p := recover(); p != nil {
			fmt.Printf("Recovered the panic(%#v).\n", p)
		}
	}()
	var mutex sync.Mutex
	fmt.Println("Lock the lock.")
	mutex.Lock()
	fmt.Println("The lock is locked.")
	fmt.Println("Unlock the lock.")
	mutex.Unlock()
	fmt.Println("The lock is unlocked.")
	fmt.Println("Unlock the lock again.")
	mutex.Unlock()
}

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var rwm sync.RWMutex
	for i := 0; i < 3; i++ {
		go func(i int) {
			fmt.Printf("Try to lock for reading... [%d]\n", i)
			rwm.RLock()
			fmt.Printf("Locked for reading. [%d]\n", i)
			time.Sleep(time.Second * 2)
			fmt.Printf("Try to unlock for reading... [%d]\n", i)
			rwm.RUnlock()
			fmt.Printf("Unlocked for reading. [%d]\n", i)
		}(i)
	}
	time.Sleep(time.Millisecond * 100)
	fmt.Println("Try to lock for writing...")
	rwm.Lock()
	fmt.Println("Locked for writing.")
}

package main

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"os/signal"
	"runtime/debug"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
)

func main() {
	go func() {
		time.Sleep(5 * time.Second)
		sendSignal()
	}()
	handleSignal()
}

func handleSignal() {
	sigRecv1 := make(chan os.Signal, 1)
	sigs1 := []os.Signal{syscall.SIGINT, syscall.SIGQUIT}
	fmt.Printf("Set notification for %s... [sigRecv1]\n", sigs1)
	signal.Notify(sigRecv1, sigs1...)
	sigRecv2 := make(chan os.Signal, 1)
	sigs2 := []os.Signal{syscall.SIGQUIT}
	fmt.Printf("Set notification for %s... [sigRecv2]\n", sigs2)
	signal.Notify(sigRecv2, sigs2...)

	var wg sync.WaitGroup
	wg.Add(2)
	go func() {
		for sig := range sigRecv1 {
			fmt.Printf("Received a signal from sigRecv1: %s\n", sig)
		}
		fmt.Printf("End. [sigRecv1]\n")
		wg.Done()
	}()
	go func() {
		for sig := range sigRecv2 {
			fmt.Printf("Received a signal from sigRecv2: %s\n", sig)
		}
		fmt.Printf("End. [sigRecv2]\n")
		wg.Done()
	}()

	fmt.Println("Wait for 2 seconds... ")
	time.Sleep(2 * time.Second)
	fmt.Printf("Stop notification...")
	signal.Stop(sigRecv1)
	close(sigRecv1)
	fmt.Printf("done. [sigRecv1]\n")
	wg.Wait()
}

func sendSignal() {
	defer func() {
		if err := recover(); err != nil {
			fmt.Printf("Fatal Error: %s\n", err)
			debug.PrintStack()
		}
	}()
	// ps aux | grep "signal" | grep -v "grep" | grep -v "go run" | awk '{print $2}'
	cmds := []*exec.Cmd{
		exec.Command("ps", "aux"),
		exec.Command("grep", "signal"),
		exec.Command("grep", "-v", "grep"),
		exec.Command("grep", "-v", "go run"),
		exec.Command("awk", "{print $2}"),
	}
	output, err := runCmds(cmds)
	if err != nil {
		fmt.Printf("Command Execution Error: %s\n", err)
		return
	}
	pids, err := getPids(output)
	if err != nil {
		fmt.Printf("PID Parsing Error: %s\n", err)
		return
	}
	fmt.Printf("Target PID(s):\n%v\n", pids)
	for _, pid := range pids {
		proc, err := os.FindProcess(pid)
		if err != nil {
			fmt.Printf("Process Finding Error: %s\n", err)
			return
		}
		sig := syscall.SIGQUIT
		fmt.Printf("Send signal '%s' to the process (pid=%d)...\n", sig, pid)
		err = proc.Signal(sig)
		if err != nil {
			fmt.Printf("Signal Sending Error: %s\n", err)
			return
		}
	}
}

func getPids(strs []string) ([]int, error) {
	var pids []int
	for _, str := range strs {
		pid, err := strconv.Atoi(strings.TrimSpace(str))
		if err != nil {
			return nil, err
		}
		pids = append(pids, pid)
	}
	return pids, nil
}

func runCmds(cmds []*exec.Cmd) ([]string, error) {
	if cmds == nil || len(cmds) == 0 {
		return nil, errors.New("The cmd slice is invalid!")
	}
	first := true
	var output []byte
	var err error
	for _, cmd := range cmds {
		fmt.Printf("Run command: %v\n", getCmdPlaintext(cmd))
		if !first {
			var stdinBuf bytes.Buffer
			stdinBuf.Write(output)
			cmd.Stdin = &stdinBuf
		}
		var stdoutBuf bytes.Buffer
		cmd.Stdout = &stdoutBuf
		if err = cmd.Start(); err != nil {
			return nil, getError(err, cmd)
		}
		if err = cmd.Wait(); err != nil {
			return nil, getError(err, cmd)
		}
		output = stdoutBuf.Bytes()
		//fmt.Printf("Output:\n%s\n", string(output))
		if first {
			first = false
		}
	}
	var lines []string
	var outputBuf bytes.Buffer
	outputBuf.Write(output)
	for {
		line, err := outputBuf.ReadBytes('\n')
		if err != nil {
			if err == io.EOF {
				break
			} else {
				return nil, getError(err, nil)
			}
		}
		lines = append(lines, string(line))
	}
	return lines, nil
}

func getCmdPlaintext(cmd *exec.Cmd) string {
	var buf bytes.Buffer
	buf.WriteString(cmd.Path)
	for _, arg := range cmd.Args[1:] {
		buf.WriteRune(' ')
		buf.WriteString(arg)
	}
	return buf.String()
}

func getError(err error, cmd *exec.Cmd, extraInfo ...string) error {
	var errMsg string
	if cmd != nil {
		errMsg = fmt.Sprintf("%s  [%s %v]", err, (*cmd).Path, (*cmd).Args)
	} else {
		errMsg = fmt.Sprintf("%s", err)
	}
	if len(extraInfo) > 0 {
		errMsg = fmt.Sprintf("%s (%v)", errMsg, extraInfo)
	}
	return errors.New(errMsg)
}

package main

import (
	"bytes"
	"fmt"
	"io"
	"math"
	"math/rand"
	"net"
	"strconv"
	"strings"
	"sync"
	"time"
)

const (
	SERVER_NETWORK = "tcp"
	SERVER_ADDRESS = "127.0.0.1:8085"
	DELIMITER      = '\t'
)

var wg sync.WaitGroup

func printLog(role string, sn int, format string, args ...interface{}) {
	if !strings.HasSuffix(format, "\n") {
		format += "\n"
	}
	fmt.Printf("%s[%d]: %s", role, sn, fmt.Sprintf(format, args...))
}

func printServerLog(format string, args ...interface{}) {
	printLog("Server", 0, format, args...)
}

func printClientLog(sn int, format string, args ...interface{}) {
	printLog("Client", sn, format, args...)
}

func strToInt32(str string) (int32, error) {
	num, err := strconv.ParseInt(str, 10, 0)
	if err != nil {
		return 0, fmt.Errorf("\"%s\" is not integer", str)
	}
	if num > math.MaxInt32 || num < math.MinInt32 {
		return 0, fmt.Errorf("%d is not 32-bit integer", num)
	}
	return int32(num), nil
}

func cbrt(param int32) float64 {
	return math.Cbrt(float64(param))
}

// 千万不要使用这个版本的read函数！
//func read(conn net.Conn) (string, error) {
//	reader := bufio.NewReader(conn)
//	readBytes, err := reader.ReadBytes(DELIMITER)
//	if err != nil {
//		return "", err
//	}
//	return string(readBytes[:len(readBytes)-1]), nil
//}

func read(conn net.Conn) (string, error) {
	readBytes := make([]byte, 1)
	var buffer bytes.Buffer
	for {
		_, err := conn.Read(readBytes)
		if err != nil {
			return "", err
		}
		readByte := readBytes[0]
		if readByte == DELIMITER {
			break
		}
		buffer.WriteByte(readByte)
	}
	return buffer.String(), nil
}

func write(conn net.Conn, content string) (int, error) {
	var buffer bytes.Buffer
	buffer.WriteString(content)
	buffer.WriteByte(DELIMITER)
	return conn.Write(buffer.Bytes())
}

func serverGo() {
	var listener net.Listener
	listener, err := net.Listen(SERVER_NETWORK, SERVER_ADDRESS)
	if err != nil {
		printServerLog("Listen Error: %s", err)
		return
	}
	defer listener.Close()
	printServerLog("Got listener for the server. (local address: %s)", listener.Addr())
	for {
		conn, err := listener.Accept() // 阻塞直至新连接到来。
		if err != nil {
			printServerLog("Accept Error: %s", err)
			continue
		}
		printServerLog("Established a connection with a client application. (remote address: %s)",
			conn.RemoteAddr())
		go handleConn(conn)
	}
}

func handleConn(conn net.Conn) {
	defer func() {
		conn.Close()
		wg.Done()
	}()
	for {
		conn.SetReadDeadline(time.Now().Add(10 * time.Second))
		strReq, err := read(conn)
		if err != nil {
			if err == io.EOF {
				printServerLog("The connection is closed by another side.")
			} else {
				printServerLog("Read Error: %s", err)
			}
			break
		}
		printServerLog("Received request: %s.", strReq)
		intReq, err := strToInt32(strReq)
		if err != nil {
			n, err := write(conn, err.Error())
			printServerLog("Sent error message (written %d bytes): %s.", n, err)
			continue
		}
		floatResp := cbrt(intReq)
		respMsg := fmt.Sprintf("The cube root of %d is %f.", intReq, floatResp)
		n, err := write(conn, respMsg)
		if err != nil {
			printServerLog("Write Error: %s", err)
		}
		printServerLog("Sent response (written %d bytes): %s.", n, respMsg)
	}
}

func clientGo(id int) {
	defer wg.Done()
	conn, err := net.DialTimeout(SERVER_NETWORK, SERVER_ADDRESS, 2*time.Second)
	if err != nil {
		printClientLog(id, "Dial Error: %s", err)
		return
	}
	defer conn.Close()
	printClientLog(id, "Connected to server. (remote address: %s, local address: %s)",
		conn.RemoteAddr(), conn.LocalAddr())
	time.Sleep(200 * time.Millisecond)
	requestNumber := 5
	conn.SetDeadline(time.Now().Add(5 * time.Millisecond))
	for i := 0; i < requestNumber; i++ {
		req := rand.Int31()
		n, err := write(conn, fmt.Sprintf("%d", req))
		if err != nil {
			printClientLog(id, "Write Error: %s", err)
			continue
		}
		printClientLog(id, "Sent request (written %d bytes): %d.", n, req)
	}
	for j := 0; j < requestNumber; j++ {
		strResp, err := read(conn)
		if err != nil {
			if err == io.EOF {
				printClientLog(id, "The connection is closed by another side.")
			} else {
				printClientLog(id, "Read Error: %s", err)
			}
			break
		}
		printClientLog(id, "Received response: %s.", strResp)
	}
}

func main() {
	wg.Add(2)
	go serverGo()
	time.Sleep(500 * time.Millisecond)
	go clientGo(1)
	wg.Wait()
}