This question appears in Mumbai University > Distributed System Subject

Marks: 5 M

Year: Dec 2015

In the usual RPC protocol, the caller and callee processes have a client – server relationship. Unlike this, the callback RPC facilitates a peer-to-peer paradigm among the participating processes. It allows a process to be both a client and a server. Callback RPC facility is very useful in certain distributed applications.

For example, remotely processed interactive applications that need user input from time to time or under special conditions for further processing require this type of facility. In such 48 applications, the client process makes an RPC to the concerned server process, and during procedure execution for the client, the server process makes a callback RPC to the client process. The client process takes necessary action based on the server’s request and returns a reply for the call back RPC to the server process. On receiving this reply, the server resumes the execution of the procedure and finally returns the result of the initial call to the client.

Note that the server may make several callbacks to the client before returning the result of the initial call to the client process.

The ability for a server to call its client back is very important, and care is needed in the design of RPC protocols to ensure that it is possible. In particular, to provide callback RPC facility, the following are necessary. Providing the server with the client’s handle. Making the client process wait for the callback RPC. Handling callback deadlocks.