go time. after

Golang time after characteristic use

time after Trigger , Example ：

package main
import (
	"fmt"
	"time"
)
func main() {
    
	fmt.Println("Start Time =", time.Now())
	a := time.After(5*time.Second)
	fmt.Println(<-a)
	fmt.Println("End Start Time =", time.Now())
}

After program running , The output is shown in the following figure ：

We see ,time After Waiting for 5 Seconds later , Returned a read-only channel. therefore , If you will After() In the select One of the statement blocks case in , Then you can make others case There is a certain length of time to listen and read 、 Write events .

If there are others within this period of time case Not readable yet 、 Can write event , This After() Where case Will end the current select, And then terminate select ( If select Not in loop ) Or enter the next round select ( If select In circulation ).

time after Set timeout , Example

package main
import (
	"fmt"
	"time"
)
func main() {
    
	ch1 := make(chan string)
	//  Activate a goroutine, but 5 Seconds before sending data 
	go func() {
    
		time.Sleep(5 * time.Second)
		ch1 <- "put value into ch1"
	}()
	select {
    
	case val := <-ch1:
		fmt.Println("recv value from ch1:",val)
		return
	//  Just wait 3 second , And then it's over 
	case <-time.After(3 * time.Second):
		fmt.Println("3 second over, timeover")
	}
}

After program running , The output is shown in the following figure ：

There is a timeout phenomenon on it , because Newly activated goroutine Wait first 5 second , Then send the data to channel ch1 in . however main goroutine Continue to run to select Sentence block , Because of the first case Conditions not met ( Be careful ,main goroutine It won't block ).

Evaluate the second case when , Will perform time.After() wait for 3 second ,3 Seconds later, the channel data returned by this function is read , So it's time to case Satisfy select Conditions , The select Because it's not in the loop , So just end ,main goroutine And so it ends . From beginning to end , Newly activated goroutine No chance to send data to ch1 in .