因为此操作是单向的，所以在传递通知时发送方可以同时做其他工作，而且可以并发传递通知。
Because the operation is one-way, the sender can go about doing other work while the notifications are being delivered, and the notifications can be delivered concurrently.
我们只要求客户端能提供订单，然后执行其他工作，因此该操作是单向的。
We want the client to be able to just place the order and continue with other work, so the operation is one-way.
下面的清单向我们展示了代码是如何工作的。
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