面试处处都是坑啊?让实现线程安全的单例,又不让用synchronizedhttps://m.toutiaocdn.com/group/6825568922264142350/?app=news_article×tamp=1589243495&use_new_style=0&req_id=20200512083134010129027033226E85A7&group_id=6825568922264142350&tt_from=android_share&utm_medium=toutiao_android&utm_campaign=client_share