【转】AtomicReference与volatile的区别

来源：AtomicReference与volatile的区别

volatile能保证可见性，但不能保证原子性。

AtomicReference在实现上用volatile来保证可见性，用Unsafe.compareAndSwapObject()来保证原子性。

 package org.liws;

 import java.util.concurrent.atomic.AtomicReference;
 import org.junit.Test;

 public class Test{

     private static volatile Integer volatileInt = 0;
     private static AtomicReference<Integer> atmicRef = new AtomicReference<Integer>(volatileInt);

     /** 验证volatile不能保证原子性 */
     @Test public void test_volatile() throws InterruptedException {
         for (int i = 0; i < 100; i++) {
             new Thread(new Runnable() {
                 @Override public void run() {
                     for (int i = 0; i < 10000; i++) {
                         volatileInt++;
                     }
                 }
             }).start();
         }
         Thread.sleep(1000);
         System.out.println(volatileInt); // out: something like 398793
     }

     /** 验证AtomicReference能保证原子性 */
     @Test public void test_AtomicReference() throws InterruptedException{
         for (int i = 0; i < 100; i++) {
             new Thread(new Runnable(){
                 @Override public void run() {
                     for (int i = 0; i < 10000; i++) {
                         while (true) {
                             Integer temp = atmicRef.get();
                             if (atmicRef.compareAndSet(temp, temp + 1)) {
                                 break;
                             }
                         }
                     }
                 }
             }).start();
         }
         Thread.sleep(1000);
         System.out.println(atmicRef.get());  // out: 1000000
     }
 }