参考：
https://stackoverflow.com/questions/8463008/multiprocessing-pipe-vs-queue
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区别：
- A Pipe() can only have two endpoints.
- A Queue() can have multiple producers and consumers.
When to use them
If you need more than two points to communicate, use a Queue().
If you need absolute performance, a Pipe() is much faster because Queue() is built on top of Pipe().
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结论：
In summary Pipe() is about three times faster than a Queue().
Queue 的底层是使用Pipe来实现的，或者说Queue是对Pipe的进一步包装，所以性能上有所下降，按照上面的参考资料显示速度降为了Pipe的3分之一，但是Queue支持的功能更加广泛，所以使用Pipe还是Queue要综合考虑性能要求及功能需求。
