Java多线程之内存可见性

public class SynchronizedDemo {
	private boolean ready = false;
	private int result = 0;
	private int number = 1;
	/**
	 * 写操作
	 */
	public void write(){
		ready = true;			//1.1
		number = 2;				//1.2
	}
	/**
	 * 读操作
	 */
	public void read(){
		if(ready){				//2.1
			result = number*3;	//2.2
		}
		System.out.println("result的值为:"+result);
	}
	private class ReadWriteThread extends Thread{
		private boolean flag;
		public ReadWriteThread(boolean flag){
			this.flag = flag;
		}
		@Override
		public void run(){
			if(flag){
				//构造方法中传入true，执行写操作
				write();
			}else{
				//构造方法中传入true，执行读操作
				read();
			}
		}
	}
	public static void main(String[] args) {
		SynchronizedDemo demo = new SynchronizedDemo();
		//启动线程执行写操作
		demo.new ReadWriteThread(true).start();
		//启动线程执行读操作
		demo.new ReadWriteThread(false).start();
	}
}

• 能够保证volatile变量的可见性
• 不能保证volatile变量复合操作的原子性

public class VolatileDemo {
	private volatile int number = 0;
	public int getNumber(){
		return this.number;
	}
	public void increase(){
		this.number++;
	}

	public static void main(String[] args) {
		final VolatileDemo demo = new VolatileDemo();
		for(int i = 0;i<500;i++){
			new Thread(new Runnable(){
				@Override
				public void run() {
					demo.increase();
				}
			}).start();;
		}
		//如果还有子线程在运行，主线程就让出cpu资源
		//直到所有子线程都运行完了，主线程再继续往下执行
		while(Thread.activeCount()>1){
			Thread.yield();
		}
		System.out.println("number:"+demo.getNumber());
	}
}