如何保证变量的原子性?

加synchronized (lock)锁, 缺点：加锁，释放锁，速度会比较慢

public class AtomDemo {
    public static void main(String[] args) {
        MyAtomThread atom = new MyAtomThread();

        for (int i = 0; i < 100; i++) {
            new Thread(atom).start();
        }
    }
}

class MyAtomThread implements Runnable {
    private volatile int count = 0; //送冰淇淋的数量
    private Object lock = new Object();

    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            //1,从共享数据中读取数据到本线程栈中.
            //2,修改本线程栈中变量副本的值
            //3,会把本线程栈中变量副本的值赋值给共享数据.
            synchronized (lock) {
                count++;
                System.out.println("已经送了" + count + "个冰淇淋");
            }
        }
    }
}