Golang sync.NewCond条件锁的用法

package main

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

func main() {
    c := sync.NewCond(&sync.Mutex{})
    queue := make([]interface{}, 0, 10)

    removeFromQueue := func(delay time.Duration) {
        time.Sleep(delay)
        c.L.Lock()
        queue = queue[1:]
        fmt.Println("Remove from queue")
        c.L.Unlock()
        c.Signal()
    }

    for i := 0; i < 10; i++ {
        c.L.Lock()
        for len(queue) == 2 {
            c.Wait()
        }

        fmt.Println("Adding to queue")
        queue = append(queue, struct{}{})
        go removeFromQueue(1 * time.Second)
        c.L.Unlock()
    }
}

程序输出如下，
Adding to queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue
Remove from queue
Adding to queue