Golang中time.After的使用理解与释放问题

package main

import (
 "fmt"
 "time"
)


func main() {
 //closeChannel()
 c := make(chan int)
 timeout := time.After(time.Second * 2) //
 t1 := time.NewTimer(time.Second * 3) // 效果相同 只执行一次
 var i int
 go func() {
 for {
 select {
 case <-c:
 fmt.Println("channel sign")
 return
 case <-t1.C: // 代码段2
 fmt.Println("3s定时任务")
 case <-timeout: // 代码段1
 i++
 fmt.Println(i, "2s定时输出")
 case <-time.After(time.Second * 4): // 代码段3
 fmt.Println("4s timeout。。。。") 
 default:    // 代码段4
 fmt.Println("default")
 time.Sleep(time.Second * 1)
 }
 }
 }()
 time.Sleep(time.Second * 6)
 close(c)
 time.Sleep(time.Second * 2)
 fmt.Println("main退出")
}

package main

import (
 "fmt"
 "time"
)

//发送者
func sender(c chan int) {
 for i := 0; i < 100; i++ {
 c <- i
 if i >= 5 {
 time.Sleep(time.Second * 7)
 } else {
 time.Sleep(time.Second)
 }
 }
}

func main() {
 c := make(chan int)
 go sender(c)
 timeout := time.After(time.Second * 3)
 for {
 select {
 case d := <-c:
 fmt.Println(d)
 case <-timeout:
 fmt.Println("这是定时操作任务 >")
 case dd := <-time.After(time.Second * 3):
 fmt.Println(dd, "这是超时*****")
 }

 fmt.Println("for end")
 }
}

// After waits for the duration to elapse and then sends the current time
// on the returned channel.
// It is equivalent to NewTimer(d).C.
// The underlying Timer is not recovered by the garbage collector
// until the timer fires. If efficiency is a concern, use NewTimer
// instead and call Timer.Stop if the timer is no longer needed.
func After(d Duration) <-chan Time {
 return NewTimer(d).C
}

package main

import "time"

func main() {
 for {
  <- time.After(10 * time.Nanosecond)
 }
}

package main

import "time"

func main() {
 for i := 0; i < 100; i++ {
  go func(){
   for {
    <- time.After(10 * time.Nanosecond)
   }
  }()
 }
 time.Sleep(1 * time.Hour)
}

select {
 case time.After(3*time.Second):
  return errTimeout
 case packet := packetChannel:
  // process packet.
}

package main

import "time"

func main() {
 for {
  select {
  case <-time.After(3 * time.Second):
  default:
  }
 }
}

package main

import "time"

func main() {
 for {
  t := time.NewTimer(3*time.Second)

  select {
  case <- t.C:
  default:
   t.Stop()
  }
 }
}