Call the Begin method, passing the callback function as the second argument and an object providing state (in this example, the client implementation of PrimeFactorizer) as the third argument.

• 调用Begin方法,将回调函数作为第二个参数传递,将提供状态的对象(在本示例中是PrimeFactorizer的客户端实现)作为第三个参数传递。