java内存模型 多线程

synchronized
volatile variable read/write
explicit lock
原子变量
monitor each object
use of classes in the java.util.concurrent package
http://www.cs.umd.edu/~pugh/java/memoryModel/
https://docs.oracle.com/javase/specs/jls/se10/html/jls-17.html

every object, in addition to having associated monitor, has an associated wait set. A wait set is a set of threads.

Object.wait
Object.notify
Object.notifyAll

rules for which values may be seen by a read of shared memory that is updated by multiple threads.

Java programming language memory model

Synchronization

communicating between threads
synchronization
which is implemented using monitors, which a thread can lock or unlock.

一个线程持有多把锁，可能会死锁。

synchronization方法：

• reads and writes of volatile variables
• the use of classes in the java.util.concurrent package

内存模型Memory Model

• 一个线程内，只有不影响最终结果，可以乱序执行
• 对于共享内存，每个线程有一份缓存，如果不是volatile变量，可能不更新缓存值
• a data race
  一个线程读
  一个线程写
  and the write and read are not ordered by synchronization