AtomicInteger在多线程下的原子性测试_JAVA_编程开发_程序员俱乐部

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使用AtomicInteger做计数器的一个例子：

class="java">package test.caipiao.log;

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

public class CounterTest {

    public static void main(String[] args) throws InterruptedException {

        final Counter counter = new Counter();

        // create 1000 threads
        ArrayList<MyThread> threads = new ArrayList<MyThread>();
        for (int x = 0; x < 1000; x++) {
            threads.add(new MyThread(counter));
        }

        // start all of the threads
        Iterator i1 = threads.iterator();
        while (i1.hasNext()) {
            MyThread mt = (MyThread) i1.next();
            mt.start();
        }

        // wait for all the threads to finish
        Iterator i2 = threads.iterator();
        while (i2.hasNext()) {
            MyThread mt = (MyThread) i2.next();
            mt.join();
        }

        System.out.println("Count: " + counter.getCount());
    }
}

// thread that increments the counter 100000 times.
class MyThread extends Thread {
    Counter counter;

    MyThread(Counter counter) {
        this.counter = counter;
    }

    public void run() {
        for (int x = 0; x < 100000; x++) {
            counter.incrementCount();
        }
    }
}

// class that uses AtomicInteger for counter
class Counter {

    private AtomicInteger count = new AtomicInteger(0);

    public void incrementCount() {
        count.incrementAndGet();
    }

    public int getCount() {
        return count.get();
    }
}

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输出如下：

Count: 100000000

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使用int做计数器的一个例子：

package test.caipiao.log;

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

public class CounterTest2 {

    public static void main(String[] args) throws InterruptedException {

        final Counter2 counter = new Counter2();

        // create 1000 threads
        ArrayList<MyThread2> threads = new ArrayList<MyThread2>();
        for (int x = 0; x < 1000; x++) {
            threads.add(new MyThread2(counter));
        }

        // start all of the threads
        Iterator i1 = threads.iterator();
        while (i1.hasNext()) {
            MyThread2 mt = (MyThread2) i1.next();
            mt.start();
        }

        // wait for all the threads to finish
        Iterator i2 = threads.iterator();
        while (i2.hasNext()) {
            MyThread2 mt = (MyThread2) i2.next();
            mt.join();
        }

        System.out.println("Count: " + counter.getCount());
    }
}

// thread that increments the counter 100000 times.
class MyThread2 extends Thread {
    Counter2 counter;

    MyThread2(Counter2 counter) {
        this.counter = counter;
    }

    public void run() {
        for (int x = 0; x < 100000; x++) {
            counter.incrementCount();
        }
    }
}

// class that uses AtomicInteger for counter
class Counter2 {

    private int count = 0;

    public void incrementCount() {
        count ++;
    }

    public int getCount() {
        return count;
    }
}

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输出如下：

Count: 43034849

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可以看到AtomicInteger例子输出结果是正确的，AtomicInteger 的incrementAndGet()是一个原子操作；

而int例子的输出结果是不正确的，int 的++不是一个原子操作。

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