未将createJobs放入goroutine为何触发Go死锁？

问题代码 #

package main

import (
    "fmt"
    "os"
    "time"
)

func main() {

    fmt.Print("wassap")

    jobs := make(chan int)
    processStarted := make(chan struct{}, 1)
    processCompleted := make(chan struct{}, 1)

    createJobs(jobs)

    go func() {
        worker(jobs, processStarted, processCompleted)
    }()

    go func() {
        sync(processStarted, processCompleted)
    }()

    time.Sleep(3600 * time.Second)
    fmt.Print("\nend of main...")

    interrupt := make(chan os.Signal)
    <-interrupt

}

func createJobs(jobs chan<- int) {
    defer close(jobs)
    for i := 1; i < 20; i++ {
        jobs <- i
    }
}

func worker(jobs <-chan int, processStarted <-chan struct{}, processCompleted <-chan struct{}) {

    for {
        select {
        case i := <-jobs:
            fmt.Printf("\nFetching job #%d from channel", i)
            time.Sleep(2 * time.Second)
        case <-processStarted:
            fmt.Print("\nProcess Started. Waiting for it to be completed")
            <-processCompleted
            fmt.Print("\nProcess completed")
        }

    }
}

func sync(processStarted chan<- struct{}, processCompleted chan<- struct{}) {

    // acquire semaphore. Send signal to channel to indicate that it is busy
    processStarted <- struct{}{}

    for i := 1; i < 5; i++ {
        fmt.Printf("\nprocessing %d", i)
        time.Sleep(5 * time.Second)
    }

    // release semaphore
    processCompleted <- struct{}{}
}

死锁原因 #

直接调用createJobs(jobs)时，核心问题出在无缓冲通道的阻塞特性：

1. jobs是无缓冲通道，无缓冲通道的发送操作必须等到有接收方准备好才能完成，否则会一直阻塞当前goroutine。
2. 主goroutine先执行createJobs(jobs)，此时worker和sync的goroutine还未启动，没有任何goroutine在接收jobs通道的数据。
3. createJobs执行到jobs <- 1时立刻阻塞，后续启动worker和sync的代码完全没有机会运行。
4. 此时程序只有主goroutine在运行，且它被无缓冲通道的发送操作卡死，没有其他goroutine能唤醒它，Go运行时检测到所有goroutine都处于休眠阻塞状态，就触发了死锁错误。

内容的提问来源于stack exchange，提问作者MrCujo