002 使用CAS自實現簡易AtomicInteger原子變量類

package org.aidan;

import java.util.concurrent.CountDownLatch;

/**
 * @author aidan
 */
public class MyAtomicInteger implements java.io.Serializable {
    private static final long serialVersionUID = -7932402631919933044L;
    private volatile int value;

    public MyAtomicInteger(int value) {
        this.value = value;
    }

    public int getValue() {
        return value;
    }

    /**
     * 相當於 原版中的 compareAndSet 方法
     *
     * @param expect
     * @param update
     * @return
     */
    public boolean cas(int expect, int update) {
        return UnsafeUtil.casInt(this, "value", expect, update);
    }

    public int incrementAndGet() {
        boolean casSuccess = false;
        for (; !casSuccess; ) {
            int value = getValue();
            casSuccess = cas(value, value + 1);
        }
        return getValue();
    }

    public static void main(String[] args) {
        final MyAtomicInteger myAtomicInteger = new MyAtomicInteger(0);
        int threadCount = 100;
        final CountDownLatch latch = new CountDownLatch(threadCount);
        for (int i = 0; i < threadCount; i++) {
            new Thread(() -> {
                myAtomicInteger.incrementAndGet();
                latch.countDown();
            }).start();
        }
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(myAtomicInteger.getValue());
    }
}

啓動100個線程，每個線程都讓MyAtomicInteger自增，最後輸出:

100