package main
 
import (
    "fmt"
    "math/rand"
    "time"
)
 
func main() {
    // 準備好三個通道。
    intChannels := [3]chan int{
        make(chan int, 1),
        make(chan int, 1),
        make(chan int, 1),
    }
    // 隨機選擇一個通道，并向它發送元素值。
    index := rand.Intn(3)
    fmt.Printf("The index: %d\n", index)
 
    //?? 取消這行代碼的注視，超時條件的選擇就會觸發。
    //intChannels[index] <- index
    // 哪一個通道中有可取的元素值，哪個對應的分支就會被執行。
    select {
    case <-intChannels[0]:
        fmt.Println("The first candidate case is selected.")
    case <-intChannels[1]:
        fmt.Println("The second candidate case is selected.")
    case elem := <-intChannels[2]:
        fmt.Printf("The third candidate case is selected, the element is %d.\n", elem)
    case <-time.After(5 * time.Second):
        fmt.Println("timed out")
    }
}

package main
 
import (
    "fmt"
    "sync"
    "time"
)
 
type Client struct {
    lock sync.Mutex //加鎖
    nextTimeOutTime time.Time //下次超時時間
}
 
const tenSec = 10
/**
刷新每次的心跳超時機制
 */
func (client *Client) freshTimeOutTime()  {
    client.lock.Lock()
    defer client.lock.Unlock()
    client.nextTimeOutTime =time.Now().Add(tenSec*time.Second)
}
 
//開啟一個gp，每隔500ms判斷有沒有超時
func (client *Client) judgeTimeOut()  {
    for  {
        time.Sleep(500*time.Millisecond)
        fmt.Printf("%v 在判斷是否超時\n", client.nextTimeOutTime)
        if time.Now().After(client.nextTimeOutTime) {
            fmt.Printf("%v 超時了\n", client.nextTimeOutTime)
        }
    }
}
 
//客戶端收到以后，修改下次心跳超時時間
func (client *Client) receiveHeart()  {
    client.freshTimeOutTime()
}
 
//開啟一個模擬ping 客戶端的線程
func pingClient(client *Client)  {
    for true {
        time.Sleep(11*time.Second)
        fmt.Printf("%v 請求發送時間\n", time.Now())
        client.receiveHeart()
    }
 
}
 
func main() {
    client := Client{
        lock:            sync.Mutex{},
        nextTimeOutTime: time.Time{},
    }
    //在當前時刻，更新下次的超時時刻是10s中后
    client.freshTimeOutTime()
 
 
    go pingClient(&client)
 
 
    go client.judgeTimeOut()
 
    for true {
 
    }
}