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Article :.NET Remoting ( Part - 3 Formatters,ObjectActivation,Proxy & Msg Sinks)
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From:
Nasha
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Hi Frndz,
Continuing our yesterdays discussion letz start with formatters.
Formatters :- .NET framework provides us with two formatters classes namely SoapFormatter and BinaryFormatter. You can find them under namespace System..Runtime.Serialization.Formatters.Binary and System.Runtime.Serialization.Formatters.Soap . Formatters are used to transfer data to and fro from a channel. They are associated with a channel through formatter sink objects and providers.Both these formatters implement a common interface know as IRemotingFormatter. IRemoting is available under System.Runtime.Remoting.Messaging Namespace. This interface has two methods Serialize and Deserialize which help to serialize data to be transfered across.
Both these formatters are primarily used for serialization and deseralization of method calls and reponses.When a method call is made , the method call information has to be serialized inorder to be sent to the remote object. To execute the request it has to be deserialized. After the request is executed on the remote object the response has to be serialized and sent. The response is further deserialised by the client.
You can also create your custom formatter and associate it to a channel.
Object Activation :- Remote objects can be either client activiated or server activated. You can get reference to the remote objects using the Activator class. Activator.GetObject method returns you a reference to the proxy of a server activated object. Activator.CreateInstance returns you a refernce to a proxy of client Activated object.
Server or WellKnown Objects :- Activator.GetObject and RemotingServices.Connect both return a reference to a proxy of a server or wellknown object. There are two types of the wellknown service type. SingleCall and Singleton.
SingleCall :- SingleCall objects dont hold any state that means for every call you make to the remote object a new object is created. So there is no object to persist data in between calls. This can be efficient as the server does not need to hold any resources for the client.
Singleton :- As the word singleton says the same object is used across client. This object can be used to share data across clients. As with any other singleton object one has to be careful of locking of resources and concurrency.
When we create a server activated remote object we can register the wellknownservicetype as either of them.
Client-Activated Objects :-Activator.CreateInstance creates a client activated object. Life-time of the client activated object is in the hands of the client unlike the server activated objects i.e. the object lives till the time the cleint wants it to live. On creating a client activated object yuo can specifiy the lease time of the object. Since the the client has reference to the object, object state can be maintained easily.
Proxy :- We just saw above that both the static methods Activator.GetObject and Activator.CreateInstance return us reference to a proxy object. In Remoting there are two types of proxies Transparent and Real Proxy. Transparent proxy is an object that looks like the remote object but all the method calls are further redirected to real proxy. Transparent proxy calls the Invoke method of the real proxy object.
To check whether the proxy received by you is a real proxy or a transparent proxy .NET provides us with a method called IsTransparentProxy exposed by RemotingServices class. This method takes the refrence to the proxy object as a parameter and returns a boolean value.
MessageSinks :- Message sinks are interceptors that can change the messages and perform some additional actions. Whenever we create an object we get a reterence to its proxy. This proxy uses a chain of envoy sinks to pass messages to the channel. All message sinks implement IMessageSink Interface which has one property NextSink and two methods SyncProcessMessage and AsyncProcessMessage.
NextSink returns a refernce to the next sink in the hierarchy to pass the message. SycnProcessMessage method processes a message request in a synchronous manner and returns a response message [ a an IMessage object ]. AsyncProcessMessage method process the message request asynchronously and returns a reference to the passed async message [ an IMessageCtrl object].
There are mainly three types of message sinks i.e. Envoy,Server Context and Object.
Envoy Sink :- They are created from the server context so the server can pass messages to the client. Envoy sinks are generally used to collect client info and pass it to the server.
Server Context Sink :- When a message is received on the server side it is passed to the server context sink.
Object Sink :- An object sink is created for a particular object if its class defines context sinks and attributes. -- Please post your queries and comments for my articles in the user group for the benefit of all. I hope this step from my end is helpful to all of us. You can find all articles written by me at my personal blog http://spaces.msn.com/members/nasha.
Regards,
Namratha (Nasha) |
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