golang select

使用场景

  select主要用来监控多个channel，channel的数据读取，写入，关闭等事件，采用的是轮训算法

监控事件

   channel读取事件
   channel的写入事件
   channel关闭事件
   其他default

读取事件

func addNumberToChan(chanName chan int) {
for {
    chanName <- 1
    time.Sleep(1 * time.Second)
}
}
// select 监控channel的push事件
  func testReadChannel()  {
var chan1 = make(chan int, 10)
var chan2 = make(chan int, 10)
go addNumberToChan(chan1)
go addNumberToChan(chan2)
for {
    select {
    case e := <- chan1 :
        fmt.Printf("Get element from chan1: %d\n", e)
    case e := <- chan2 :
        fmt.Printf("Get element from chan2: %d\n", e)
    default:
        fmt.Printf("No element in chan1 and chan2.\n")
        time.Sleep(1 * time.Second)
    }
}
}

写入事件

 func testAddChannel()  {
   var chan1 = make(chan int, 10)
   var chan2 = make(chan int, 10)

    chan1 <- 1
    chan2 <- 0
//go addNumberToChan(chan1)
//go addNumberToChan(chan2)

for {
    select {
    case chan1 <- 1 :
        fmt.Printf("Get element from chan1: 1")
    case chan2 <- 0 :
        fmt.Printf("Get element from chan2: 0")
    default:
        fmt.Printf("No element in chan1 and chan2.\n")
        time.Sleep(1 * time.Second)
    }
}

}

PS:注意select语句如果做监听使用的话，尽量嵌套在for循环中，因为单独的select是阻塞的，并且是又返回值的，eg:

   func server1(ch chan string) {
time.Sleep(1 * time.Second)
ch <- "from server1"
   }
   func server2(ch chan string) {
time.Sleep(1 * time.Second)
ch <- "from server2"

   }
   func main() {
output1 := make(chan string,1)
output2 := make(chan string,1)
go server1(output1)
go server2(output2)
select {
case s1 := <-output1:
    fmt.Println(s1)
case s2 := <-output2:
    fmt.Println(s2)
    }

这个程序的结果要么是“from server1”或者“from server2”，因为select读取到一个数据后就返回了