Tomcat中多线程开发中Reload报错问题。

目前项目使用的JFinal，项目使用了一个线程池来管理下载线程，然后重启Tomcat有时候会报如下错误。
Illegal access: this web application instance has been stopped already. Could not load com.mchange.v2.c3p0.impl.IdentityTokenResolvableBeanInfo. The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
大概原因是因为在tomcat重启的时候，之前的Tomcat的线程还没有完全关闭。
如何能保证重启的时候，能把线程全部关闭？
什么设置标志位，都不管用，有没有办法强制关闭某个线程。