python两种实现多线程的方式及实例
http://www.tutorialspoint.com/python/python_multithreading.htm
python中介绍的生产者消费者、信号量、队列等问题
http://www.laurentluce.com/posts/python-threads-synchronization-locks-rlocks-semaphores-conditions-events-and-queues/