(C#) 多线程修改布尔值， volatile

参考： https://msdn.microsoft.com/en-us/library/x13ttww7(VS.80).aspx

http://stackoverflow.com/questions/2474945/is-it-safe-to-use-a-boolean-flag-to-stop-a-thread-from-running-in-c-sharp

https://msdn.microsoft.com/en-us/library/7a2f3ay4(v=vs.80).aspx