public final int incrementAndGet() {for (;;) {int current = get(); //从主内存中拷贝value放到本地线程栈内存中 这二行代码可能另一个线程也在执行int next = current + 1; //做增加操作if (compareAndSet(current, next)) return next;}}
//调用unsafe的compareAndSwapInt方法
public final boolean compareAndSet(int expect, int update) {return unsafe.compareAndSwapInt(this, valueOffset, expect, update);}public final int get() {return value;}private volatile int value;  //volatile保证了可见性，在incrementAndGet()方法中get（）方法获取的value是从主内存中拿到的

private static final Unsafe unsafe = Unsafe.getUnsafe(); 

private static final long valueOffset;static {        try {         valueOffset = unsafe.objectFieldOffset (AtomicInteger.class.getDeclaredField("value")); //获取value值在AtomicInteger内存地址中的偏移量

        }catch (Exception ex)         { throw new Error(ex); } } 

//Unsafe class 代码 public final native boolean compareAndSwapInt(Object var1, long var2, int var4, int var5);

UNSAFE_ENTRY(jboolean, Unsafe_CompareAndSwapInt(JNIEnv *env, jobject unsafe, jobject obj, jlong offset, jint e, jint x))UnsafeWrapper("Unsafe_CompareAndSwapInt");oop p = JNIHandles::resolve(obj);jint* addr = (jint *) index_oop_from_field_offset_long(p, offset);return (jint)(Atomic::cmpxchg(x, addr, e)) == e;
UNSAFE_END

// Adding a lock prefix to an instruction on MP machine
// VC++ doesn't like the lock prefix to be on a single line
// so we can't insert a label after the lock prefix.
// By emitting a lock prefix, we can define a label after it.
#define LOCK_IF_MP(mp) __asm cmp mp, 0  \__asm je L0      \__asm _emit 0xF0 \__asm L0:inline jint     Atomic::cmpxchg    (jint     exchange_value, volatile jint*     dest, jint     compare_value) {// alternative for InterlockedCompareExchangeint mp = os::is_MP();  //判断当前系统环境__asm {mov edx, dest   mov ecx, exchange_valuemov eax, compare_valueLOCK_IF_MP(mp)cmpxchg dword ptr [edx], ecx}
}