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Instead of using the new operator to instantiate remote objects, we can use the
Activator class. Behind the scenes in the implementation of the new operator
this class is used not only for remote but also for local object instantiations. For well-known
objects the static method GetObject() returns a proxy to the remote object.
Using Activator.GetObject() instead of the new operator we no longer need
to register the well known client type, because the URL to the remote object must be passed as argument
to the GetObject() method:
// Create and register the client channel
TcpClientChannel channel = new TcpClientChannel();
ChannelServices.RegisterChannel(channel);
MyRemoteObject obj = (MyRemoteObject)Activator.GetObject(
typeof(MyRemoteObject),
"tcp://localhost:9000/SimpleServer/MyRemoteObject");Whether we use the new operator or the Activator.GetObject() method is just
a matter of choice. The new operator is easier to use and hides the fact that we deal
with remote objects. GetObject() is nearer to the reality as the name of this method
clearly shows that a new object does not get instantiated. We already know that with both versions
when we use well-known objects a proxy is returned, and no connection to the server happens at
this time.
Well-known objects can be in SingleCall mode or Singleton. With the
SingleCall mode an object is created with every method call; with a Singleton
only one object is created in all. Singleton objects can be used to share information
between multiple clients.
Using a configuration file the only change that must be done to the server is setting the
mode attribute of the <wellknown> element to Singleton:
<wellknown
mode="Singleton"
type="Wrox.Samples.MyRemoteObject, MyRemoteObject"
objectUri="MyRemoteObject" />Without using a configuration file, the enumeration WellKnownObjectMode.SingleCall has to
be replaced with WellKnownObjectMode.Singleton:
WellKnownServiceTypeEntry remObj = new WellKnownServiceTypeEntry(
typeof(MyRemoteObject),
"SimpleServer/MyRemoteObject",
WellKnownObjectMode.Singleton);
RemotingConfiguration.RegisterWellKnownServiceType(remObj);No changes are required for the client.
Multiple threads are used on the server to fulfill concurrent requests from clients. We have to develop this remote object in a thread-safe manner. For more about thread issues see the Wrox book Professional C#.
One more aspect of singletons that must be thought of is scalability. A
Singletonobject can't be spread across multiple servers. If scalability across multiple servers may be needed, don't use singletons.
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Created: February 25, 2002
Revised: February 25, 2002
URL: http://webreference.com/programming/csharp/webservices/chap6/2/3.html
