The WCF server invokes the callback function one-way-double-pass operation mode:

The server-side server implements the callback interface interface definition. The client implements the callback interface interface implementation, thus implementing the server side via var channel = operationcontent.current.getcallbackchannel</* Interface class name */> (); Gets the callback instance object channel; The client implementation-related callback interface can be invoked on the server side by channel. This approach is most used in the way the heartbeat packets are implemented in distributed servers. Easily use two-way mode + delegate to implement event-driven clustered distributed WCF data servers

The WCF server invokes the callback function one-way-double-pass operation mode: