协程顺序打印和交替打印

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package main
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import (
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  "fmt"
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  "sync"
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)
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func main() {
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  fmt.Println("=====通过 channel 顺序打印=====")
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  printOrderlyByChannel()
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  fmt.Println("=====通过 WaitGroup 顺序打印=====")
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  printOrderlyByWaitGroup()
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}
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// 协程顺序打印 A B C
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func printOrderlyByChannel() {
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  wg := &sync.WaitGroup{}
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  wg.Add(3)
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  ch := make(chan string)
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  ch2 := make(chan string)
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  go func ()  {
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    defer wg.Done()
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    fmt.Println("A")
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    ch <- "B"
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  }()
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  go func ()  {
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    defer wg.Done()
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    fmt.Println(<- ch)
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    ch2 <- "C"
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  }()
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  go func ()  {
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    defer wg.Done()
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    fmt.Println(<- ch2)
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  }()
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  wg.Wait()
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}
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func printOrderlyByWaitGroup() {
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  wg := &sync.WaitGroup{}
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  wg.Add(1)
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  go func ()  {
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    fmt.Println("A")
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    wg.Done()
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  }()
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  wg.Wait()
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  wg.Add(1)
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  go func ()  {
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    fmt.Println("B")
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    wg.Done()
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  }()
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  wg.Wait()
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  wg.Add(1)
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  go func ()  {
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    fmt.Println("C")
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    wg.Done()
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  }()
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  wg.Wait()
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}

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func main() {
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  wg := &sync.WaitGroup{}
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  wg.Add(2)
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  chA := make(chan int, 1)
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  chB := make(chan int)
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  chA <- 1
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  go func() {
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    defer wg.Done()
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    for i := 0; i < 3; i++ {
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      <-chA
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      fmt.Println(string(rune('a' + i)))
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      chB <- 1
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    }
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  }()
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  go func() {
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    defer wg.Done()
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    for i := 0; i < 3; i++ {
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      <-chB
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      fmt.Println(i + 1)
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      if i == 2 {
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        break
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      }
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      chA <- 1
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    }
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  }()
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  wg.Wait()
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}