The following describes the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. In descriptions of this application, “/” represents an “or” relationship between associated objects unless otherwise specified. For example, A/B may represent A or B. The term “and/or” in this application describes only an association relationship between associated objects and indicates that three relationships may exist. For example, A and/or B may indicate the following three cases: only A exists, both A and B exist, and only B exists, where A and B may be singular or plural. In addition, in the descriptions of this application, “a plurality of” means two or more than two. “At least one item (piece) of the following” or a similar expression thereof refers to any combination of these items, including any combination of a singular item (piece) or plural items (pieces). For example, at least one of a, b, or c may indicate a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c may be singular or plural. In addition, for convenience of clear description of the technical solutions in the embodiments of this application, terms such as “first” and “second” are used in the embodiments of this application to distinguish between same objects or similar objects that have basically same functions and purposes. A person skilled in the art may understand that the terms such as “first” and “second” do not intend to limit a quantity or an execution sequence, and the terms such as “first” and “second” do not indicate a definite difference.