Advanced Topics in Visual Studio .NET

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Advanced Topics
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Return New TimeSpan(0, 0, 10) Else Return TimeSpan.Zero End If End Function End Class
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Using the CalculatorSponsorEx class is conceptually similar to having the client manu ally call the lease s Renew method but offers more flexibility. For example, you can have one sponsor for each distinct client application, and thus a single call to the SetState method from a client would extend the lifetime of all the remote objects that have been returned to that specific client.
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The ClientSponsor Class
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Interestingly, the .NET Framework defines a class named ClientSponsor that works much like the initial version of the CalculatorSponsor class. This generic sponsor extends the lease time of the associated object by the TimeSpan value that you pass to its constructor or assign to its RenewalTime property. For example, here s how you might use this generic sponsor with a remotable object from inside the Calculator class:
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Get a reference to the lease object.
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Dim lease As ILease = DirectCast(calc.GetLifetimeService(), ILease)
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Create a generic sponsor that will renew for half a minute, and register it.
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Dim mysponsor As New ClientSponsor(New TimeSpan(0, 0, 30)
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lease.Register(mysponsor)
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If you later want to double the renewal time...
mysponsor.RenewalTime = New TimeSpan(0, 1, 0)
This is what you do to prevent the sponsor from renewing the lease.
mysponsor.RenewalTime = TimeSpan.Zero
Defining a Tracking Handler
A tracking handler is an object that receives a notification when an object is mar shaled, unmarshaled, or disconnected. From the developer s perspective, a tracking handler is a public class that implements the System.Runtime.Remoting.Ser vices.ITrackingHandler interface. Here s a simple tracking handler that displays diag nostic messages in the console window:
Public Class CustomTracker Implements ITrackingHandler Public Sub DisconnectedObject(ByVal obj As Object) _ Implements ITrackingHandler.DisconnectedObject Console.WriteLine( CustomTracker.DisconnectedObject {0}", obj) End Sub Public Sub MarshaledObject(ByVal obj As Object, ByVal ref As ObjRef) _ Implements ITrackingHandler.MarshaledObject
32:
Remoting
Console.WriteLine( CustomTracker.MarshaledObject {0}", obj) If Not ref.URI Is Nothing Then Console.WriteLine( URI = {0}", ref.URI) End Sub Public Sub UnmarshaledObject(ByVal obj As Object, ByVal ref As ObjRef) _ Implements ITrackingHandler.UnmarshaledObject Console.WriteLine( CustomTracker.UnmarshaledObject {0}", obj) If Not ref.URI Is Nothing Then Console.WriteLine( URI = {0}", ref.URI) End Sub End Class
The URI information displayed when an object is marshaled or unmarshaled is a path that the .NET remoting architecture generates for internal use; it can be useful in the debug phase to distinguish objects of the same class. (See Figure 32-6.)
Figure 32-6 Tracking handlers let you display notification messages when a remote object is marshaled, unmarshaled, or disconnected.
The host application must register the handler object by passing it to the RegisterTrack ingHandler method of the TrackingServices class, also in the System.Runtime.Remot ing.Services namespace:
(In the host application.)
Dim tracker As New CustomTracker
TrackingServices.RegisterTrackingHandler(New tracker)
You can later unregister the handler by calling the UnregisterTrackingHandler method and retrieve the array of all the registered handlers with the RegisteredHandlers property.
Metadata Deployment
For simplicity s sake, all the samples you ve seen so far assumed that the client applica tion has access to the DLL containing the remote object (RemoteComponents.dll in this case). In real-world distributed applications, this assumption is quite unrealistic, for at least a couple of reasons. First, distributing the DLL containing the remote objects makes deployment a nightmare, especially if you plan to frequently release new versions. Sec ond, in many cases you don t want to give your remote clients the real DLL that runs on the server, because malicious users might reverse-engineer the assembly and borrow your code for use in other projects or access data that should be kept secret.
Part VII:
Advanced Topics
There are three solutions to this issue: using the SoapSuds utility, creating an assembly that defines a public interface, or creating an assembly that defines a public base class. Let s examine the pros and cons of each.
Using the SoapSuds Tool
The client application needs to access the object s metadata for two reasons: to instan tiate the object with a New keyword and to reference the object using a strongly typed variable. If the client can t access the remote object s metadata, these operations would fail with an error at run time. You can provide your clients with the remote object s metadata without giving them the actual assembly by compiling an assembly (known as proxy assembly) that con tains the same classes with the same methods as the real assembly, but without any code inside those methods. Once compiled, all the classes in this proxy assembly would have the same identity as the actual assembly, and a strongly typed object could be assigned a reference to the remote object without a glitch. While in theory this approach is feasible, in practice maintaining two source code sets (or using compilation constants and tons of #If statements) to generate the two assem blies is problematic at the least. Fortunately, the SoapSuds tool can create the proxy assembly for you.
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