This is where. NET Remoting comes into the picture. NET Remoting allows two independent application domains to interact among themselves. What is. NET Remoting exactly? NET Remoting is a framework where you can invoke or consume methods or objects in a remote computer named the server from your computer, the client. We can also perform asynchronous calls in. NET Remoting using callback delegates. How to do. NET Remoting In order to do. NET Remoting, we need to have a server that holds the instance of the Remoting service object and a client that connects to the server to use the Remoting object.
There may be more than one client using objects remotely from a server. More than one server cannot be started since there is a common port to listen to remote client applications. The client will not understand the objects in the remote without the use of a proxy class.
The proxy classes are used in web services as well. We use a transparent proxy class. When we invoke methods of this proxy, the proxy redirects these calls to a. NET Remoting server. All the. All Remoting objects must be inherited from this class. Then, in the server-side classes, we need to use the following keywords: All the Remoting classes and methods are from the namespace system. We need to use RemoteConfiguration. Configure to configure a Remoting server. This configuration is done in the form of an XML file.
For example: RemotingConfiguration. All these should be included inside a tag and described in the well-known section. The client-side will be the same with minor changes. This is listed below: Here, the problem of creating objects is clarified and we must look at how these objects are activated. These objects are activated using server-side activation and client-side activation.
The server-side activation has two steps, namely, singleton and singlecall. Singleton Objects : These objects share data service multiple clients.
Client-Activated Objects : They are the ones which are activated once they get a call from the client. To create an object, we must declare a remotable class. It is to note that the class has to inherit the MarshalByRefObject. To do this, Open a new project of Class library type.
Now to create object of this class remotely, we must build a host application which registers our created class and a channel for remoting. Create it in the same directory where you have addsubs. And compile it to dll our code will be using host. The host. Configure "host. WriteLine "Your requests Press Enter to exit" ; Console.
Our application must reside in the client application domain to use. NET Remoting system. For this we will create a client. Save the above as client. Keep a note on the directory where you save these files. You should save the client. Scenarios that are often well suited for the SingleCall activation mode are those applications where the object is required by the client to do a small amount of work and then the object is no longer required. Some common examples include retrieving the inventory level for an item, displaying tracking information for a shipment, and so on.
In the Singleton activation mode, there is at most one instance of the remote object, regardless of the number of clients accessing it. A Singleton mode object can maintain state information across the method calls. Therefore, they are also sometimes known as stateful objects. The state maintained by the Singleton mode server-activated object is globally shared by all its clients.
A Singleton object does not exist on the server forever. Its lifetime is determined by the lifetime lease of the object. I'll discuss lifetime leases shortly in the section, "Lifetime Leases. Singleton activation mode is useful in scenarios such as in a chat server where multiple clients talk to the same remote object and share data between one another.
Client-activated objects CAOs are those remote objects whose lifetime is directly controlled by the client. This is in direct contrast with SAOs, where the server, not the client, has complete control over objects' lifetimes. Client-activated objects are instantiated on the server as soon as the client requests the object to be created. You can use any of the available constructors of the remotable class to create a CAO. A typical CAO activation involves the following steps:.
When the client attempts to create an instance of the server object, an activation request message is sent to the remote server. The server then creates an instance of the requested class by using the specified constructor and returns an ObjRef object to the client application that invoked it. The ObjRef object contains all the required information to generate a proxy object that is capable of communicating with a remote object.
The client uses the ObjRef object to create a proxy of the server object on the client side. An instance of the CAO serves only the client that was responsible for its creation, and the CAO doesn't get discarded with each request. The lifetime of a CAO is determined by the lifetime leases. I'll talk more about this topic shortly in a section titled "Lifetime Leases. CAOs are useful in scenarios such as entering a complex purchase order where multiple roundtrips are involved and clients want to maintain their own private state with the remote object.
Based on the discussions in the previous section, the various object activation techniques can be compared as shown in Figure 3. SingleCall server activation mode offers maximum scalability because the remote object occupies server resources for the minimum length of the time. This enables the server to allocate its resources between many clients. On the other hand, the client activation of remote objects offers maximum flexibility because you have complete control over the construction and lifetime of the remote object.
A lifetime lease is the period of time that a particular object shall be active in memory before the. NET framework deletes it and reclaims its memory. Custom and Infinite Lifetimes A remote object can choose to have a custom defined lifetime if the InitializeLifetimeService method of the base class, MarshalByRefObject , is overridden.
If the InitializeLifetimeService method returns a null , the type tells the. NET remoting system that its instances are intended to have an infinite lifetime. A lifetime lease is represented by an object that implements the ILease interface that is defined in the System.
Lifetime namespace. Some of the important members of this interface are listed in Table 3. Gets the amount of time remaining on the lease before the object is marked for garbage collection.
Gets or sets the initial time for the lease. If the object does not receive any method calls, it lives for only this period. Gets or sets the amount of time by which a call to the remote object will increase the CurrentLeaseTime. When an object is created, the value of the InitialLeaseTime property which is by default 5 minutes is used to set its lifetime lease CurrentLeaseTime.
Whenever the object receives a call, its CurrentLeaseTime is increased by the time specified by value of RenewOnCallTime property which is by default 2 minutes. The client can also renew a lease for a remote object by directly calling the ILease. Renew method:. When the value of CurrentLeaseTime reaches 0 , the. NET Framework contacts any sponsors registered with the lease to check whether they are ready to sponsor a renewal of the lease of the object. If the sponsor does not renew the object or the server cannot contact the sponsor within the duration specified by the SponsorshipTimeout property, then the object is marked for garbage collection.
Sponsors are the objects responsible for dynamically renewing an object's lease if its lease expires. Sponsors implement the ISponsor interface and are registered with the lease manager by calling the ILease. Register method. When the lease for such an object expires, the lease manager calls the ISponsor. Renewal method implemented by the sponsor objects to renew the lease time. For more information about sponsors, refer to the "Renewing Leases" topic in the. The MBR remotable objects can be activated in two modes: server-activated mode and client-activated mode.
You can activate SAOs in two ways: SingleCall object is created for each client request and Singleton object is created once on the server and is shared by all clients. The SingleCall activation mode provides the maximum scalability because it does not maintain any state and the object lives for the shortest duration possible. CAOs are created for each client when the client requests that a remote object be created. These objects maintain state for each client with which they are associated.
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