Go语言使用select{}阻塞main函数介绍

func main() {
    for i := 0; i < 20; i++ { //启动20个协程处理消息队列中的消息
        c := consumer.New()
        go c.Start()
    }
    select {} // 阻塞
}

func main(){
 var count int
 for {
  select {
  case <-time.Tick(time.Millisecond * 500):
   fmt.Println("咖啡色的羊驼")
   count++
   fmt.Println("count--->" , count)
  case <-time.Tick(time.Millisecond * 499) :
   fmt.Println(time.Now().Unix())
   count++
   fmt.Println("count--->" , count)
  }
 }
}

func main(){
 t1 := time.Tick(time.Second)
 t2 := time.Tick(time.Second)
 var count int
 for {
  select {
  case <-t1:
   fmt.Println("咖啡色的羊驼")
   count++
   fmt.Println("count--->" , count)
  case <-t2 :
   fmt.Println(time.Now().Unix())
   count++
   fmt.Println("count--->" , count)
  }
 }
}

1535673600
count---> 1
1535673600
count---> 2
1535673601
count---> 3

咖啡色的羊驼
count---> 1
1535673600
count---> 2
咖啡色的羊驼
count---> 3
1535673601
count---> 4

func selectgo(sel *hselect) int {
 // ...
 // case洗牌
 pollslice := slice{unsafe.Pointer(sel.pollorder), int(sel.ncase), int(sel.ncase)}
 pollorder := *(*[]uint16)(unsafe.Pointer(&pollslice))
 for i := 1; i < int(sel.ncase); i++ {
  //....
 }
 // 给case排序
 lockslice := slice{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
 lockorder := *(*[]uint16)(unsafe.Pointer(&lockslice))
 for i := 0; i < int(sel.ncase); i++ {
  // ...
 }
 for i := int(sel.ncase) - 1; i >= 0; i-- {
  // ...
 }
 // 加锁该select中所有的channel
 sellock(scases, lockorder)
 // 进入loop
loop:
 // ... 
 // pass 1 - look for something already waiting
 // 按顺序遍历case来寻找可执行的case
 for i := 0; i < int(sel.ncase); i++ {
  //...
  switch cas.kind {
  case caseNil:
   continue
  case caseRecv:
   // ... goto xxx
  case caseSend:
   // ... goto xxx
  case caseDefault:
   dfli = casi
   dfl = cas
  }
 }
 // 没有找到可以执行的case，但有default条件，这个if里就会直接退出了。
 if dfl != nil {
  // ...
 }
 // ...
 // pass 2 - enqueue on all chans
 // chan入等待队列
 for _, casei := range lockorder {
  // ...
  switch cas.kind {
  case caseRecv:
   c.recvq.enqueue(sg)
  case caseSend:
   c.sendq.enqueue(sg)
  }
 }
 // wait for someone to wake us up
 // 等待被唤起,同时解锁channel(selparkcommit这里实现的)
 gp.param = nil
 gopark(selparkcommit, nil, "select", traceEvGoBlockSelect, 1)
 
 // 突然有故事发生，被唤醒，再次该select下全部channel加锁
 sellock(scases, lockorder)
 // pass 3 - dequeue from unsuccessful chans
 // 本轮最后一次循环操作，获取可执行case，其余全部出队列丢弃
 casi = -1
 cas = nil
 sglist = gp.waiting
 // Clear all elem before unlinking from gp.waiting.
 for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink {
  sg1.isSelect = false
  sg1.elem = nil
  sg1.c = nil
 }
 gp.waiting = nil
 for _, casei := range lockorder {
  // ...
  if sg == sglist {
   // sg has already been dequeued by the G that woke us up.
   casi = int(casei)
   cas = k
  } else {
   c = k.c
   if k.kind == caseSend {
    c.sendq.dequeueSudoG(sglist)
   } else {
    c.recvq.dequeueSudoG(sglist)
   }
  }
  // ...
 }
 // 没有的话，再走一次loop
 if cas == nil {
  goto loop
 }
 // ...
bufrecv:
 // can receive from buffer
bufsend:
 // ...
recv:
 // ...
rclose:
 // ...
send:
 // ...
retc:
 // ...
sclose:
 // send on closed channel
}