tick實現定時任務

1. 示例程式碼

   package main
   
   import (
   	"fmt"
   	"math/rand"
   	"time"
   )
   
   // schedule task
   func tack(ticker <-chan time.Time) {
       // for 迴圈中不斷執行select
   	for {
   		var flag = 0
   		select {
   		case <-ticker:
   			flag += rand.Intn(1000)
   			fmt.Printf("**********task<%d>**********\n", flag)
   		default:
   			time.Sleep(1)
   		}
   	}
   }
   
   // fake competitor
   func competitor() {
   	for {
   		fmt.Printf("competitor running...\n")
   		// goroutine 是搶佔式的，必須顯式地讓出CPU資源去處理其它任務
   		time.Sleep(time.Millisecond)
   	}
   }
   
   // runner
   func run() {
   	// for {}
   	time.Sleep(time.Second * 5)
   }
   
   func main() {
       // Tick 返回一個長度為1的channel
   	ticker := time.Tick(time.Second * 2)
   	go tack(ticker)
   	go competitor()
   	run()
   }
    
   

2. 原始碼分析

   // Tick is a convenience wrapper for NewTicker providing access to the ticking
   // channel only. While Tick is useful for clients that have no need to shut down
   // the Ticker, be aware that without a way to shut it down the underlying
   // Ticker cannot be recovered by the garbage collector; it "leaks".
   // Unlike NewTicker, Tick will return nil if d <= 0.
   func Tick(d Duration) <-chan Time {
   	if d <= 0 {
   		return nil
   	}
   	return NewTicker(d).C		//