ActomicInteger源码解析

public final int incrementAndGet() {
        for (;;) {
            int current = get();
            int next = current + 1;
            if (compareAndSet(current, next))
                return next;
        }
    }

public final boolean compareAndSet(int expect, int update) {

        return unsafe.compareAndSwapInt(this, valueOffset, expect, update);

    }
Unsafe里的CAS操作相关：
//第一个参数o为给定对象，offset为对象内存的偏移量，通过这个偏移量迅速定位字段并设置或获取该字段的值，
//expected表示期望值，x表示要设置的值，下面3个方法都通过CAS原子指令执行操作。
public final native boolean compareAndSwapObject(Object o, long offset,Object expected, Object x);                                                                                                  
 
public final native boolean compareAndSwapInt(Object o, long offset,int expected,int x);

public final native boolean compareAndSwapLong(Object o, long offset,long expected,long x);