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package goConcurrency
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import (
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"fmt"
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"math/rand"
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"sync"
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"time"
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)
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func SelectStmt() {
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// 声明需要的变量
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var a [4]int // 注意后边索引的使用
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var c1, c2, c3, c4 = make(chan int), make(chan int), make(chan int), make(chan int)
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//var i1, i2 = 0, 42
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var i1 = 0
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// 操作channel的goroutine
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go func() {
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c1 <- 10
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}()
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go func() {
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<-c2
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}()
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go func() {
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close(c3)
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}()
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go func() {
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c4 <- 40
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}()
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// select 多路监听的goroutine
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go func() {
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select {
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// 监听是否可以从 c1 中接收值
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case i1 = <-c1:
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println("received ", i1, " from channel c1")
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// 监听对c2的写操作
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//case c2 <- i2:
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// println("sent ", i2, " to channel c2")
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case c2 <- i2Value():
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println("sent ", i2Value(), " to channel c2")
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// 监听c3的关闭状态
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case i3, ok := <-c3:
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if ok {
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println("received ", i3, " from channel c3")
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} else {
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println("channel c3 was closed")
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}
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// 测试左值表达式的执行时机
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case a[f()] = <-c4:
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println("received ", a[f()], " from channel c4")
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// 默认case
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default:
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println("on channel operation.")
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}
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}()
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// 简单阻塞，等待goroutine执行完毕
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time.Sleep(100 * time.Millisecond)
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}
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func i2Value() int {
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println("send value is evaluate")
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return 42
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}
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func f() int {
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print("f() is running.")
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return 2
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}
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func SelectBlock() {
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// 空select阻塞
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//println("before select")
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//select {} // block()
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//println("after select")
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// nil select阻塞
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var ch chan int // nil channel, 不能receive和send
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go func() {
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ch <- 1024
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println("send data")
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}()
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println("before select")
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select {
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case <-ch:
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case ch <- 42:
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}
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println("after select")
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}
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func SelectNilChannel() {
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// 一，初始化channel
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ch := make(chan int) // non nil channel
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// 二，操作channel的goroutine
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go func() {
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// 随机写入int
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rand.Seed(time.Now().Unix())
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for {
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ch <- rand.Intn(10)
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time.Sleep(400 * time.Millisecond)
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}
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}()
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// 三，select处理定时内的channel
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// 到达时间，停止处理
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go func() {
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// 设置定时器
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t := time.After(3 * time.Second)
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sum := 0
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for {
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select {
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case v := <-ch:
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println("received value ", v)
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sum += v
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case <-t:
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// 将 channel 设置为 nil，不再处理ch
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ch = nil
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println("ch was set inl, sum is ", sum)
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}
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}
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}()
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time.Sleep(5 * time.Second)
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}
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//func main() {
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// println("before select")
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// select {} // block()
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// println("after select")
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//}
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func SelectFor() {
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// 定义channel
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ch := make(chan int)
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// 操作Channel
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// send to channel
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go func() {
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for {
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// 模拟演示数据来自于随机数
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//实操时，数据可以来自各种I/O，例如网络、缓存、数据库等
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ch <- rand.Intn(100)
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time.Sleep(200 * time.Millisecond)
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}
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}()
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// 监控Channel
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go func() {
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// 持续监控
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for {
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select {
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case v := <-ch:
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println("received from channel, value is ", v)
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}
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}
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}()
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time.Sleep(3 * time.Second)
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}
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func SelectNonBlock() {
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// 一，初始化数据
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counter := 10 // 参与人数
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max := 20 // [0, 19] // 最大范围
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rand.Seed(time.Now().UnixMilli())
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answer := rand.Intn(max) // 随机答案
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println("The answer is ", answer)
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println("------------------------------")
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// 正确答案channel
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bingoCh := make(chan int, counter)
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// 二，模拟猜
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// wg
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wg := sync.WaitGroup{}
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wg.Add(counter)
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for i := 0; i < counter; i++ {
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// 每个goroutine代表一个猜数字的人
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go func() {
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defer wg.Done()
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result := rand.Intn(max)
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println("someone guess ", result)
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// 答案争取，写入channel
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if result == answer {
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bingoCh <- result
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}
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}()
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}
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wg.Wait()
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println("------------------------------")
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// 三，检测是否有人猜中
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select {
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case result := <-bingoCh:
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println("some one hint the answer ", result)
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default:
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// 非阻塞的保证，存在default case
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println("no one hint the answer")
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}
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}
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func SelectRace() {
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// 一，初始化数据
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// 模拟查询结果，需要与具体的querier建立联系
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type Rows struct {
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// 数据字段
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// 索引标识
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Index int
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}
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// 模拟的querier数量
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const QuerierNum = 8
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// 用于通信的channel，数据，停止信号
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ch := make(chan Rows, 1)
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stopChs := [QuerierNum]chan struct{}{}
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for i := range stopChs {
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stopChs[i] = make(chan struct{})
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}
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// wg,rand
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wg := sync.WaitGroup{}
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rand.Seed(time.Now().UnixMilli())
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// 二，模拟querier查询，每个查询持续不同的时间
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wg.Add(QuerierNum)
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for i := 0; i < QuerierNum; i++ {
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// 每一个 querier
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go func(i int) {
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defer wg.Done()
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// 模拟执行时间
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randD := rand.Intn(1000)
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println("querier ", i, " start fetch data, need duration is ", randD, " ms.")
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// 查询结果的channel
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chRst := make(chan Rows, 1)
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// 执行查询工作
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go func() {
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// 模拟时长
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time.Sleep(time.Duration(randD) * time.Millisecond)
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chRst <- Rows{
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Index: i,
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}
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}()
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// 监听查询结果和停止信号channel
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select {
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// 查询结果
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case rows := <-chRst:
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println("querier ", i, " get result.")
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// 保证没有其他结果写入，才写入结果
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if len(ch) == 0 {
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ch <- rows
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}
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// stop信号
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case <-stopChs[i]:
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println("querier ", i, " is stopping.")
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return
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}
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}(i)
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}
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// 三，等待第一个查询结果的反馈
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wg.Add(1)
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go func() {
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defer wg.Done()
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// 等待ch中传递的结果
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select {
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// 等待第一个查询结果
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case rows := <-ch:
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println("get first result from ", rows.Index, ". stop other querier.")
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// 循环结构，全部通知querier结束
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for i := range stopChs {
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// 当前返回结果的goroutine不需要了，因为已经结束
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if i == rows.Index {
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continue
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}
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stopChs[i] <- struct{}{}
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}
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// 计划一个超时时间
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case <-time.After(5 * time.Second):
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println("all querier timeout.")
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// 循环结构，全部通知querier结束
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for i := range stopChs {
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stopChs[i] <- struct{}{}
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}
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}
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}()
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wg.Wait()
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}
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func SelectAll() {
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// 一，初始化资源
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// 整体的资源类型
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type Content struct {
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Subject string
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Tags []string
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Views int
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// 标识操作了资源的哪个部分
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part string
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}
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// 三个用于表示不同部分的常量
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const (
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PartSubject = "subject"
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PartTags = "tags"
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PartViews = "views"
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)
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// 同步停止的信号channel的map
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stopChs := map[string]chan struct{}{
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PartSubject: make(chan struct{}),
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PartTags: make(chan struct{}),
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PartViews: make(chan struct{}),
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}
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// 接收和发送操作的通信channel
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ch := make(chan Content, len(stopChs))
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// timeover 表示超时的channel
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to := time.After(time.Millisecond * 800)
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// waitgroup
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wg := sync.WaitGroup{}
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// 初始化全局随机数种子
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rand.Seed(time.Now().UnixMilli())
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// 二，goroutine执行每个部分的获取
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// 为每个部分的处理使用goroutine完成
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for part := range stopChs {
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wg.Add(1)
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go func(part string) {
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defer wg.Done()
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// 一，初始化信息
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randD := rand.Intn(1000) //ms
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fmt.Println("start fetch ", part, " data, need duration is ", randD, " ms.")
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// 查询结果的channel
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chRst := make(chan Content, 1)
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// 二，模拟延时的获取资源
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go func() {
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// 模拟执行时间
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time.Sleep(time.Duration(randD) * time.Millisecond)
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// 模拟业务逻辑
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content := Content{
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part: part,
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}
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// 基于不同的part，完成不同属性的设置
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switch part {
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case PartSubject:
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content.Subject = "Subject of content"
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case PartTags:
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content.Tags = []string{"go", "Goroutine", "Channel", "select"}
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case PartViews:
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content.Views = 1024
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}
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// 发送到rstCh
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chRst <- content
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}()
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// 三，监控资源获取成功还是超时到达
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select {
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// 查询到结果
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case rst := <-chRst:
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fmt.Println("querier ", part, " get result.")
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ch <- rst
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// 超时到了
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case <-stopChs[part]:
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fmt.Println("querier ", part, " is stopping.")
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return
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}
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}(part)
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}
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// 三，接收每个部分，整合在一起
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wg.Add(1)
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go func() {
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defer wg.Done()
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// 一，初始化资源
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// 整体的资源
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content := Content{}
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// 标识哪个部分已经接收完毕
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received := map[string]struct{}{}
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// 二，等待接收或者超时到期
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// 超时时间到要通知未完成的goroutine结束
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// 未到超时时间，将结果整合到一起，并判定是否需要继续等待
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loopReceive:
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for {
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select {
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// 超时
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case <-to:
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println("querier timeout. Content is incomplete.")
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// 超时时间到要通知未完成的goroutine结束
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// 遍历stopCh,判定是否存在与received中即可
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for part := range stopChs {
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if _, exists := received[part]; !exists {
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// 不存在，说明没有处理完，应该技术
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stopChs[part] <- struct{}{}
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}
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}
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// 关闭
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close(ch)
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// 不再继续监听了，结束！
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break loopReceive
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// 有处理完毕的业务
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case rst := <-ch:
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println("received some part ", rst.part)
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// 根据不同的part，更新整体content的字段
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// 同时要记录，哪个part已经完成接收了
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switch rst.part {
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case PartSubject:
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content.Subject = rst.Subject
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received[PartSubject] = struct{}{}
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case PartTags:
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content.Tags = rst.Tags
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received[PartTags] = struct{}{}
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case PartViews:
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content.Views = rst.Views
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received[PartViews] = struct{}{}
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}
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// 判定是否已经接收完毕，需要继续等待
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finish := true // 完成标志
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// 确认是否都接收了
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for part := range stopChs {
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if _, exists := received[part]; !exists {
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// 不存在，说明存在没有处理完毕的，没有结束
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finish = false
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break
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}
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}
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// 判定 finish
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if finish {
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// 说明，全部已经处理完毕，结束了！
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fmt.Println("all querier finished. Content is complete")
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close(ch)
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break loopReceive
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}
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}
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}
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// 三，输出结果
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fmt.Println("content:", content)
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}()
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wg.Wait()
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}
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func SelectChannelCloseSignal() {
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wg := sync.WaitGroup{}
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// 定义无缓冲channel
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// 作为一个终止信号使用（啥功能的信号都可以，信号本身不分功能）
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ch := make(chan struct{})
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// goroutine，用来close, 表示发出信号
|
|
|
wg.Add(1)
|
|
|
go func() {
|
|
|
defer wg.Done()
|
|
|
time.Sleep(2 * time.Second)
|
|
|
fmt.Println("发出信号, close(ch)")
|
|
|
close(ch)
|
|
|
}()
|
|
|
|
|
|
// goroutine，接收ch，表示接收信号
|
|
|
wg.Add(1)
|
|
|
go func() {
|
|
|
defer wg.Done()
|
|
|
// 先正常处理，等待ch的信号到来
|
|
|
for {
|
|
|
select {
|
|
|
case <-ch:
|
|
|
fmt.Println("收到信号, <-ch")
|
|
|
return
|
|
|
default:
|
|
|
|
|
|
}
|
|
|
// 正常的业务逻辑
|
|
|
fmt.Println("业务逻辑处理中....")
|
|
|
time.Sleep(300 * time.Millisecond)
|
|
|
}
|
|
|
}()
|
|
|
|
|
|
wg.Wait()
|
|
|
}
|
