1、The user should be able to exploit the concurrency error in this web application and view login information for another user that is attempting the same function at the same time. This will require the use of two browsers. Valid user names are 'jeff' and 'dave'.
Please enter your username to access your account.
同时开2个浏览器，分别请求jeff 和 dave的数据，然后同时请求。
但是因为没有考虑到多线程安全的问题，然后后面返回的结果会冲掉之前的。
设计程序时，需要考虑线程安全问题。