java线程和操作系统线程之间的关系：
java线程管理是JVM的一部分，虽然大部分JVM直接映射java线程到底层系统线程，但是还是java的线程管理决定谁有机会运行
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The thread scheduler is the part of the JVM (although most JVMs map Java threads directly to native threads on the underlying OS) that decides which thread should run at any given moment, and also takes threads out of the run state. Assuming a single processor machine, only one thread can actually run at a time. Only one stack can ever be executing at one time. And it's the thread scheduler that decides which thread—of all that are eligible—will actually run. |
参考资料：
1. Java线程学习和总结: http://blog.csdn.net/fantian830211/article/details/784597