看到一篇非常简洁的解释并发（Concurrent）与并行（Parallel）的区别的文章，纪录一下，以供参考。原文出自：http://joearms.github.io/2013/04/05/concurrent-and-parallel-programming.html
What’s the difference between concurrency and parallelism?
Explain it to a five year old.
Concurrent = Two queues and one coffee machine.
Parallel = Two queues and two coffee machines.
