为什么此Go程序未按预期进入死锁状态？

Question

I am a newbie in Go, i wrote this code and hope it will enter deadlock status, but failed.

var mux sync.Mutex

func main() {
    runtime.GOMAXPROCS(1)
    for i := 0; i < 3; i++ {
    go func() {
        log.Println("Trying to Lock the Mux")
        mux.Lock()
        log.Println("The mux is Locked")
    }()
  }
  runtime.Gosched()
}
//Output:
//2017/01/17 08:59:42 Trying to Lock the Mux
//2017/01/17 08:59:42 The mux is Locked
//2017/01/17 08:59:42 Trying to Lock the Mux
//2017/01/17 08:59:42 Trying to Lock the Mux

As you can see. this code run well and print something and then quit without any deadlock error. For I know, the first go func(){} goroutine has returned and locked the mux then quit. But the other two goroutines will be blocked because the mux has already blocked.

The function runtime.Gosched() should push the main goroutine to the only FIFO queue(runtime.GOMAXPROCS(1)) right? why it can be excute before the left two goroutine that already in the queue?

BTW,this following code will return the deadlock error as expected

var mux sync.Mutex

func main() {
    runtime.GOMAXPROCS(1)
    var wg sync.WaitGroup
    wg.Add(3)
    for i := 0; i < 3; i++ {
        go func() {
            defer wg.Done()
            log.Println("Trying to Lock the Mux")
            mux.Lock()
            log.Println("The mux is Locked")

        }()
    }
    wg.Wait()
}

Thanks!

Answer 1

For your code:

var mux sync.Mutex

func main() {
    runtime.GOMAXPROCS(1)
    for i := 0; i < 3; i++ {
    go func() {
        log.Println("Trying to Lock the Mux")
        mux.Lock()
        log.Println("The mux is Locked")
    }()
  }
  runtime.Gosched()
}

There is no deadlock, for

func (m *Mutex) Lock()

Lock locks m. If the lock is already in use, the calling goroutine blocks until the mutex is available.

So the second and third goroutine just wait there. This is busy waiting. then the main goroutine exit, so the second and third goroutine also exist.