Why does using a copy of Sync.WaitGroup in an external function lead to missing output in a goroutine?

Using Sync.WaitGroup with External Functions

In the code provided, the intention is for the primary goroutine to print numbers from 1 to 11 by utilizing a channel and a wait group. However, it occasionally skips number 11, resulting in an incomplete output.

The issue arises from the incorrect传递 of sync.WaitGroup to the external function, Print. By passing a copy of WaitGroup to the function, it can't perform the necessary Done() call on the original wait group being waited on by the main goroutine.

Best Solution:

The recommended solution involves modifying the code as follows:

<code class="go">func main() {
    ch := make(chan int)

    var wg sync.WaitGroup
    wg.Add(2)

    go Print(ch, &wg)

    go func() {
        for i := 1; i <= 11; i++ {
            ch <- i
        }
        close(ch)
        defer wg.Done()
    }()

    wg.Wait()
}

func Print(ch <-chan int, wg *sync.WaitGroup) {
    for n := range ch { // reads from channel until it's closed
        fmt.Println(n)
    }
    defer wg.Done()
}</code>

In this fix, the Print function receives a pointer to the wait group, ensuring that its Done() method is called within the function, thus allowing the main goroutine to proceed correctly.

Alternative Solution:

Alternatively, one can eliminate the need for WaitGroup within the Print function by directly closing the channel after sending all numbers:

<code class="go">func Print(ch <-chan int) {
    for n := range ch { // reads from channel until it's closed
        fmt.Println(n)
    }
}</code>

In this case, the main goroutine must wait on the channel's closure instead:

<code class="go">wg.Wait()
close(ch)</code>

The above is the detailed content of Why does using a copy of Sync.WaitGroup in an external function lead to missing output in a goroutine?. For more information, please follow other related articles on the PHP Chinese website!