一、測試int為執行緒不安全

在java中，高併發/多執行緒情況下，int的自增自減操作都不是執行緒安全的，使用AtomicInteger可以保證。

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(){ //測試，輸出結果隨機，為執行緒不安全
        for(;loop<100000;loop++) {
            add();
        }
    }
    public void testAtomicInteger(){  //輸出1000000，執行緒安全
        for(;atomicLoop.getAndAdd(1)<100000;) {
            add();
        }
    }
    @Override
    public String toString() {
        return ""+shareI;
    }
}
 

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(){ //執行緒不安全的
        for(;looper.getLoop()<100000;looper.setLoop(looper.getLoop()+1)){
            add();
        }
    }
    public void testUseAtomic(){
        AtomicIntegerFieldUpdater<Looper> atomicIntegerFieldUpdater =  //使用Atomic來進行自加
                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;  //對於AtomicIntegerFieldUpdater要控制的欄位必須為public volatile
    public int getLoop() {
        return loop;
    }
    public void setLoop(int loop) {
        this.loop = loop;
    }
}