happens-before原则

 下面是java内存模型下一些“天然”的先行发生关系，这些先行发生关系无须任何同步器协助就已经存在，可以在编码中直接使用。如果两个操作之间的关系不再此列，并且无法从下面规则中推导出来，则它们就没有顺序性保障，虚拟机可以对它们进行任意地重排序。

 

1.Program order rule. Each action in a thread happens-before every action in
 that thread that comes later in the program order.

    程序次序规则：在一个线程内，按照程序代码的顺序，书写在前面的操作先行发生与书写在后面的操作。

 

2.Monitor lock rule. An unlock on a monitor lock happens-before every subsequent
 lock on that same monitor lock.

   冠程锁定规则：一个锁的unlock操作先行发生于“后面”对同一个锁的lock操作。这里的“后面”是指时间上的先后顺序。

 

3.Volatile variable rule. A write to a volatile field happens-before every
 subsequent read of that same field.

 volatile变量规则：对一个volatile变量的写操作先行发生于“后面”对这个变量的读操作。这里的“后面”同样是指时间上的先后顺序。

 

4.Thread start rule. A call to Thread.start on a thread happens-before any 
other thread detects taht thread has terminated, either by successfully 
return from Thread.join or by Thread.isAlive returning false.

 线程的启动规则：Thread对象的start()方法先行发生于此线程的没一个动作。

 

5.Interruption rule. A thread calling interrupt on another thread 
happens-before the interrupted thread detects the interrupt( either by
 having InterruptedException thrown, or invoking isInterrupted or
 interrupted).

 线程中断规则：对线程的interrupt()方法的调用先行发生于被中断线程的代码检测。

6.Finalizer rule. The end of a constrcutor for an object happens-before the
 start of the finalizer for that obejct.

 对象终结原则：一个对象的初始化完成（构造函数执行完成）先行发生与它的finalize()方法的开始。

 

7.Transitivity. If A happens-before B, and B happens-before C, then A 
happens-before C.

 传递性：你懂的。