volatile关键字

package com.bjsxt.base.sync007;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * volatile关键字不具备synchronized关键字的原子性（同步）
 * 可以使用AtomicInteger 替代普通变量或者用 synchronized修饰方法
 * @author alienware
 *
 */
public class VolatileNoAtomic extends Thread{
	private static volatile int count;
	//private static AtomicInteger count = new AtomicInteger(0);
	/*synchronized*/
	private static void addCount(){
		for (int i = 0; i < 1000; i++) {
			count++ ;
			//count.incrementAndGet();
		}
		System.out.println(count);
	}
	
	public void run(){
		addCount();
	}
	
	public static void main(String[] args) {
		
		VolatileNoAtomic[] arr = new VolatileNoAtomic[100];
		for (int i = 0; i < 10; i++) {
			arr[i] = new VolatileNoAtomic();
		}
		
		for (int i = 0; i < 10; i++) {
			arr[i].start();
		}
	}
	
	
	
	
}

 

package com.bjsxt.base.sync007;

public class RunThread extends Thread{
    /*没有 volatile 关键字试一下 */
	private volatile boolean isRunning = true;
	private void setRunning(boolean isRunning){
		this.isRunning = isRunning;
	}
	
	public void run(){
		System.out.println("进入run方法..");
		int i = 0;
		while(isRunning == true){
			//..
		}
		System.out.println("线程停止");
	}
	
	public static void main(String[] args) throws InterruptedException {
		RunThread rt = new RunThread();
		rt.start();
		Thread.sleep(1000);
		rt.setRunning(false);
		System.out.println("isRunning的值已经被设置了false");
	}
	
	
}

 

package com.bjsxt.base.sync007;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

public class AtomicUse {

	private static AtomicInteger count = new AtomicInteger(0);
	
	//多个addAndGet在一个方法内是非原子性的，需要加synchronized进行修饰，保证4个addAndGet整体原子性
	//也就是说你 同一个方法里，同时使用多个count.addAndGet 原子性就失去了。
	/**synchronized*/
	public  int multiAdd(){
			try {
				Thread.sleep(100);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			count.addAndGet(1);
			count.addAndGet(2);
			count.addAndGet(3);
			count.addAndGet(4); //+10
			return count.get();
	}
	
	
	public static void main(String[] args) {
		
		final AtomicUse au = new AtomicUse();

		List<Thread> ts = new ArrayList<Thread>();
		for (int i = 0; i < 100; i++) {
			ts.add(new Thread(new Runnable() {
				@Override
				public void run() {
					System.out.println(au.multiAdd());
				}
			}));
		}

		for(Thread t : ts){
			t.start();
		}


	
		

		
	}
}