如何让 TCP 出现 Accept()错误？

	ctx := context.Background()

	for {
		conn, err := l.listener.Accept()
		if err != nil {
			// Close() was probably called.
        	// 想要走到这里，执行这行代码
			connRefuse.Add(1)
			return
		}

		acceptTime := time.Now()

		connectionID := l.connectionID
		l.connectionID++

		connCount.Add(1)
		connAccept.Add(1)

		go func() {
			if l.PreHandleFunc != nil {
				conn, err = l.PreHandleFunc(ctx, conn, connectionID)
				if err != nil {
					log.Errorf("mysql_server pre hook: %s", err)
					return
				}
			}

			l.handle(conn, connectionID, acceptTime)
		}()
	}