Go - receiving from an empty channel

package main

import (
    "fmt"
    "sync"
    "time"
)

var workers = 3

func processItem(input <-chan int, output chan<- int, wg *sync.WaitGroup) {
    for {
        fmt.Println("=")
        in := <-input
        fmt.Printf("Working on input: %v\n", in)
        time.Sleep(2 * time.Second)
        output <- in + 1
        wg.Done()
    }
}

func main() {
    items := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

    var wg sync.WaitGroup
    wg.Add(len(items))
    out := make(chan int, len(items))
    in := make(chan int)

    for i := 0; i < workers; i++ {
        go processItem(in, out, &wg)
    }

    for _, val := range items {
        in <- val
    }

    wg.Wait()

    total := 0
    for j := 0; j < len(items); j++ {
        total += <-out
    }
    fmt.Printf("Total sum is : %v\n", total)
}

zzh@ZZHPC:/zdata/MyPrograms/Go/ddd$ go run main.go
=
Working on input: 1
=
Working on input: 2
=
Working on input: 3
=
Working on input: 4
=
=
Working on input: 5
Working on input: 6
=
Working on input: 7
=
Working on input: 8
=
Working on input: 9
=
Working on input: 10
=
=
=
Total sum is : 65

"Working on input"输出有10个，"="输出有13个，说明函数processItem中的for循环是因为语句“in := <-input”而退出的（从空channel中接收不到数据会导致goroutine异常退出）。