各位大佬，下面的 Go 代码中，当主 Goroutine 执行到 c.Wait() 的时候，第 28 行的 c.L.Lock() 肯定执行了，那么当执行到第 17 行的 c.L.Lock()，为什么程序不会一直阻塞呢？

package main import ( "fmt" "sync" "time" ) // a goroutine that is waiting for a signal, and a goroutine that is sending signals. // Say we have a queue of fixed length 2, and 10 items we want to push onto the queue func main() { c := sync.NewCond(&sync.Mutex{}) queue := make([]interface{}, 0, 10) removeFromQueue := func(delay time.Duration) { time.Sleep(delay) c.L.Lock() // 这是第 17 行，执行到这里为什么不是一直阻塞等待锁？ queue = queue[1:] fmt.Println("Removed from queue") c.L.Unlock() c.Signal() // let a goroutine waiting on the condition know that something has ocurred } for i := 0; i < 10; i++ { c.L.Lock() // 这是 28 行，critical section // When the queue is equal to two the main goroutine is suspend // until a signal on the condition has been sent length := len(queue) fmt.Println(length) for len(queue) == 2 { fmt.Println("wait signal") c.Wait() // 这是 36 行，等待 signal ，但是 removeFromQueue 为什么不会一直等待锁呢？ } fmt.Println("Adding to queue") queue = append(queue, struct{}{}) go removeFromQueue(10 * time.Second) c.L.Unlock() } }