java中的自增过程不是原子性操作

在java中多线程访问同一数据时，会出现数据不一致的问题。java中的自增操作需要多步完成，而且不是原子性操作控制。下面的代码说明了问题，源自java编程思想

</pre><pre code_snippet_id="1623662" snippet_file_name="blog_20160325_2_1202041" name="code" class="java">package synchonize;public class EvenGenerator extends IntGenerator {private int currentEvenValue = 0;public int next(){++currentEvenValue;Thread.yield();++currentEvenValue;return currentEvenValue;}public static void main(String []args){EvenChecker.test(new EvenGenerator());}}

package synchonize;public abstract class IntGenerator {private volatile boolean canceled = false;public abstract int next();public void cancel(){canceled = true;}public boolean isCanceled(){return canceled;}}

package synchonize;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class EvenChecker implements Runnable{private IntGenerator generator;private final int id;public EvenChecker(IntGenerator g, int id){this.generator = g; this.id = id;}public void run() {// TODO Auto-generated method stubwhile(!generator.isCanceled()){int val = generator.next();if(val %2 !=0){System.out.println(val + "not even!");generator.cancel();}}}public static void test(IntGenerator gp, int count){System.out.println("press control-c to exit");ExecutorService exec = Executors.newCachedThreadPool();for(int i=0; i < count; i++){exec.execute(new EvenChecker(gp, i));}exec.shutdown();}public static void test(IntGenerator gp){test(gp, 10);}}

好不容易调出这个结果来

press control-c to exit
5not even!
3not even!
7not even!
3not even!