AtomicInteger是基于CAS实现的一个线程安全的整型类,Unsafe调用CPU底层指令实现原子操作
// java.util.concurrent.atomic.AtomicInteger
public final int getAndIncrement() {
return unsafe.getAndAddInt(this, valueOffset, 1);
}
public final int getAndDecrement() {
return unsafe.getAndAddInt(this, valueOffset, -1);
}
// sun.misc.Unsafe
public final int getAndAddInt(Object o, long offset, int delta) {
int v;
do {
v = getIntVolatile(o, offset);
} while (!compareAndSwapInt(o, offset, v, v + delta));
return v;
}
public native int getIntVolatile(Object o, long offset);
public final native boolean compareAndSwapInt(Object o, long offset, int expected, int x);