自定义实现 AtomicInteger 类

其实获得了 Unsafe 之后直接调 API 就行。

package dongguabai.atomic;

import org.springframework.objenesis.instantiator.util.UnsafeUtils;
import sun.misc.Unsafe;

/**
 * @author Dongguabai
 * @description
 * @date 2021-02-21 19:53
 */
public class MyAtomicInteger {

    private volatile int value;

    private static final long valueOffset;

    private static final Unsafe UNSAFE = UnsafeUtils.getUnsafe();

    static {
        try {
            valueOffset = UNSAFE.objectFieldOffset(MyAtomicInteger.class.getDeclaredField("value"));
        } catch (NoSuchFieldException e) {
           throw new RuntimeException(e);
        }
    }

    public final int incrementAndGet() {
        return UNSAFE.getAndAddInt(this, valueOffset, 1) + 1;
    }

    public final int incrementAndGet2() {
        int i;
        while (true){
            i = value+1;
            if (UNSAFE.compareAndSwapInt(this,valueOffset,value,i)){
                return i;
            }
        }
    }
}

测试：

package dongguabai.atomic;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * @author Dongguabai
 * @description
 * @date 2021-02-21 16:35
 */
public class AtomicIntegerDemo {

    static int i ;

    static AtomicInteger j = new AtomicInteger(0);

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

        System.out.println("i++：");
        for (int k = 0; k < 10; k++) {
            new Thread(()-> System.out.println(++i)).start();
        }
        Thread.sleep(1000);
        System.out.println("\nAtomicInteger：");
        for (int k = 0; k < 10; k++) {
            new Thread(()-> System.out.println(j.incrementAndGet())).start();
        }
        Thread.sleep(1000);
        System.out.println("\nAtomicInteger：");
        MyAtomicInteger myAtomicInteger = new MyAtomicInteger();
        for (int k = 0; k < 10; k++) {
            new Thread(()-> System.out.println(myAtomicInteger.incrementAndGet())).start();
        }

        Thread.sleep(1000);
        System.out.println("\nAtomicInteger2：");
        MyAtomicInteger myAtomicInteger2 = new MyAtomicInteger();
        for (int k = 0; k < 10; k++) {
            new Thread(()-> System.out.println(myAtomicInteger2.incrementAndGet2())).start();
        }
    }
}

输出结果：

i++：
1
2
3
4
5
6
7
8
9
10

AtomicInteger：
1
2
3
4
5
6
7
8
9
10

AtomicInteger：
1
2
3
4
5
6
7
8
9
10

AtomicInteger2：
1
2
3
4
5
6
7
8
9
10