java语言规范
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阅读了2.17 Execution，2.15 Arrays，The?class?File Format
http://java.sun.com/docs/books/jvms/second_edition/html/Concepts.doc.html#16491
阅读8.1 Terminology and Framework至8.7章节
主内存和工作内存，read(main)、load(thread)、assign(thread)、store(thread)、write(main)、lock and unlock(thread)
线程之间不直接交互，都是通过主内存来交互的。
double和long双字节操作是非原子的，thread从main read-load是按单字节进行的
volatile只是轻量级的同步，保证可见性。thread use 之前会先从main load一把，thread在assign之后会紧跟着store一把。对volatile的操作是非原子的，写操作不能依赖于当前值，比如自增操作。
Locking can guarantee both visibility and atomicity; volatile variables can only guarantee visibility.
阅读8.7-8.14，完成第8章
class SynchSynchSimple {
??? int a = 1, b = 2;
??? synchronized void to() {
??? a = 3;
??? b = 4;
??? }
??? synchronized void fro()?
??? System.out.println("a= " + a + ", b=" + b);
??? }
}
一个时刻只能有一个线程获得对象锁，也就是说to fro不可能同时进行。There is a lock associated with every object，synchronized 其实是在执行方法体之前获得对象锁(锁和条件变量notify之类是java同步的两个重要武器)
Locking is not just about mutual exclusion; it is also about memory visibility
object.wait and object.notify()
http://www.zeroup.org/javas-synchronized-object-wait-object-notify-notifyall-works.html
如何获得对象锁
? * <li>By executing a synchronized instance method of that object.
???? * <li>By executing the body of a synchronized} statement
???? *???? that synchronizes on the object.
???? * <li>For objects of type Class,} by executing a
???? *???? synchronized static method of that class.
使用场景：并发对象发生变化调用notify,不可操作并发对象时调用wait。总是要先获得对象锁才能调用objg.wait()，总是以循环的形式使用wait.
http://suo.iteye.com/blog/1199694
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