java的int类型线程安全

一、测试int为线程不安全

在java中，高并发/多线程情况下，int的自增自减操作都不是线程安全的，使用AtomicInteger可以保证。

package com.yezi.learn.atomic;
import java.util.concurrent.atomic.AtomicInteger;
/**
 * Created by yezi on 2014/5/10.
 */
public class TestAtomicInteger {
    private int shareI=0;
    private AtomicInteger atomicLoop = new AtomicInteger(0);
    private int loop =0;
    public static void main(String []args) throws Exception{
        TestAtomicInteger t = new TestAtomicInteger();
        t.testMethod();
        System.out.println(t);
    }
    public void testMethod() throws Exception{
        Thread th1 = new Thread(new ThreadTest());
        Thread th2 = new Thread(new ThreadTest());
        th1.start();
        th2.start();
        th1.join();
        th2.join();
    }
    public synchronized void add(){
        shareI++;
    }
    class ThreadTest implements Runnable{
        @Override
        public void run() {
            //testAtomicInteger();
            testInt();
        }
    }
    public void testInt(){ //测试，输出结果随机，为线程不安全
        for(;loop<100000;loop++) {
            add();
        }
    }
    public void testAtomicInteger(){  //输出1000000，线程安全
        for(;atomicLoop.getAndAdd(1)<100000;) {
            add();
        }
    }
    @Override
    public String toString() {
        return ""+shareI;
    }
}

二、AtomicIntegerFieldUpdater可以对Obj的字段进行处理

package com.yezi.learn.atomic;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
/**
 * Created by yezi on 2014/5/10.
 */
public class TestAtomicObjectInteger {
    private Looper looper = new Looper();
    private int shareI=0;
    public static void main(String ...args) throws Exception{
        TestAtomicObjectInteger t = new TestAtomicObjectInteger();
        t.testMethod();
        System.out.println(t);
    }
    public void testNormal(){ //线程不安全的
        for(;looper.getLoop()<100000;looper.setLoop(looper.getLoop()+1)){
            add();
        }
    }
    public void testUseAtomic(){
        AtomicIntegerFieldUpdater<Looper> atomicIntegerFieldUpdater =  //使用Atomic来进行自加
                AtomicIntegerFieldUpdater.newUpdater(Looper.class,"loop");
        for(;atomicIntegerFieldUpdater.getAndAdd(looper,1)<100000;){
            add();
        }
    }
    public void testMethod() throws Exception{
        Thread th1 = new Thread(new ThreadTest());
        Thread th2 = new Thread(new ThreadTest());
        th1.start();
        th2.start();
        th1.join();
        th2.join();
    }
    class ThreadTest implements Runnable{
        @Override
        public void run() {
            testUseAtomic();
            //testNormal();
        }
    }
    public synchronized void add(){
        shareI++;
    }
    @Override
    public String toString() {
        return shareI+"";
    }
}
class Looper{
    public volatile int loop=0;  //对于AtomicIntegerFieldUpdater要控制的字段必须为public volatile
    public int getLoop() {
        return loop;
    }
    public void setLoop(int loop) {
        this.loop = loop;
    }
}