Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

Figure 12-3: How .NET Remoting marshals objects by reference.The .NET Remoting implementation of MBR provides for a proxy/stub pair and aphysical channel for network transportation. The proxy represents the remote object tothe client, as it simply mirrors the same set of methods and properties. Each clientinvocation of a remote method actually hits the local proxy, which, in turn, takes care ofrouting the call down to the server. A method invocation originates a message thattravels on top of a channel and a transmission protocol.Each message passes through a chain of hook objects (called sinks) on each side ofthe transport channel. Sinks are nearly identical to Windows hooks. By defining andregistering a sink, the programmer can perform a specific operation at a specific stageof the remoting process. Because the creation of the proxy takes place automatically,the programmer has little to do other than creating an instance of the target object andissuing the call.If the object resides in an external AppDomain, the remoting infrastructure creates alocal proxy for it to perform the requested operation. But how can the code determinewhether a given object is local, lives in a remote AppDomain, or just doesn't exist? Inspite of the sophisticated code that constitutes the remoting infrastructure,programming remote objects is mostly a matter of setup. Once the client has beenproperly configured, you normally create a new instance of the remote class using thenew operator, no matter what type of class you're calling and where it resides. Clientsmust declare to the CLR which classes are remote and provide connection information.Remote objects, in turn, must be publicly available and bound to a given channel.The MarshalByRefObject ClassInheriting from the MarshalByRefObject class is the key that enables user classes to beaccessed across AppDomain boundaries in applications that support remoting.MarshalByRefObject is the base class for objects that communicate acrossAppDomains. Serializable classes that do not inherit from MarshalByRefObject, wheninstantiated from a remote assembly, are implicitly marshaled by value. Other classesare simply considered nonremotable.So if you want to write a remote component that uses the network efficiently and alwaysruns on the server, the only thing you have to do is create the class inheriting fromMarshalByRefObject, as follows:public class NorthwindService : MarshalByRefObject430