What is the major use of MarshalByRefObject?

Solution 1:

Remoting; it means that between AppDomains or machines, rather than serialize and transfer the object, the object stays at one end and a proxy is created at the other. All method calls to the proxy are intercepted and the call is transmitted as RPC ^{wiki, msdn}, causing the method to execute on the other machine (typically serialising the arguments and return value).

Note: this can lead to unexpectedly "chatty" interfaces. The object/proxy/RPC approach is now less preferable to approaches with an explicit service boundary; Microsoft now recommends WCF ^{wiki, msdn} instead of remoting.

Solution 2:

Another important use of MarshalByRefObject is for implementing AOP via remoting sink-chains.

If you have an object that derives from ContextBoundObject (which itself derives from MarshalByRefObject) you can instantiate it in a separate Context within the same AppDomain and have communications between objects automatically go through the Remoting proxy system - allowing you to plug custom sinks into the Remoting sink-chain.

This ultimately allows you to 'decorate' method calls to your objects and implement cross-cutting services, such as logging and security etc.