为什么golang ticker.Stop（）在tickerTest1中不起作用？

Question

I know the Stop function can not close the channel. I am just confused with the two different results of tickerTest1 and tickerTest2.

package main

import (
    "time"
    "log"
)

func tickerTest1() {
    ticker := *time.NewTicker(time.Second)
    count := 0
    go func() {
        time.Sleep(3*time.Second)
        ticker.Stop()
    }()
    for range ticker.C {
        count ++
        log.Println("tickerTest1：", count)
    }
}

func tickerTest2() {
    ticker := time.NewTicker(time.Second)
    count := 0
    go func() {
        time.Sleep(3*time.Second)
        ticker.Stop()
    }()
    for range ticker.C {
        count ++
        log.Println("tickerTest2：", count)
    }
}

func main() {
    go tickerTest1()
    tickerTest2()
}

Answer 1

tickerTest2() works as expected, so let's examine tickerTest1().

time.NewTicker() returns a pointer value, a value of type *time.Ticker. This already hints you should use it as that: as a pointer (and should not dereference it).

Yet, you dereference it by using the indirection operator:

ticker := *time.NewTicker(time.Second)

By dereferencing it,ticker will be of type time.Ticker, a non-pointer type. And its value will be a copy of the value pointed by the pointer that NewTicker() returns.

This alone wouldn't be a problem, because Go automatically takes the address of ticker whenever you call a method with pointer receiver on it (such as Ticker.Stop()). But the address that is passed as the receiver will be the address of this ticker variable, and any method that modifies the time.Ticker struct will only modify this distinct copy, and not the time.Ticker value that is pointed by the return value of the NewTicker() function.

So in effect, you only stop the copy Ticker stored in the ticker variable, and not the original Ticker that was returned by NewTicker() and which is actually sending the values on the channel. That remains unstopped.