Remoting in C#

While you are developing distributed application by csharp, you might need to have communication between objects that run in different processes.
.NET remoting enables client applications to use objects in other processes on the same computer or on any other computer available on its network.(MSDN)

Each remoting application consist of three part:

• A remotable object.

• A host application domain to listen for requests for that object.

• A client application domain that makes requests for that object.

We have two kind of remotable objects, one Marshal-by-value objects and Marshal-by-reference objects.

• Marshal-by-value objects are either inherited from ISerializable interface or using a Serializable attribute, which are copied and passed from the application domain.
• Marshal-by-reference objects are the objects from a class which is inherited from MarshalByRefObject class.

Notice that the objects from other classes which are not in that two types cannot be used in remoting.

Part 1: Remotable Types
In my first post about remoting I will create a class named "MyRemotableType" which is a Marshal-by-reference type, and I will put this class into a class library with name MyRemotableTypes.dll.

public class MyRemotableType:MarshalByRefObject
{
public MyRemotableType()
{
Console.WriteLine("A New MarshalByRefObject created");
}
public void AddNumbers(int a,int b)
{
Console.WriteLine("Sum is : {0}",a+b);
}
public string CaldSum(int a,int b)
{
return string.Format("Sum is: {0}", a + b);
}
}


Notice that Marshal-by-reference objects needs to be activated. Activation for Marshal-by-reference objects has two types:

• Server activation: which means that objects will be created by server at the first method call, but not when the object is initializing by calling new keyword.
  
• Client activation: which means that objects will be created by server when the client calls the new keyword.

Server activation it self contains two types, which can be specified with using WellKnownObjectMode enumeration items:

• Singleton: It means that there will always be only one instance, regardless of how many clients there are for that object, and which have a default lifetime.
• SingleCall: It means that the system creates a new object for each client method invocation.

Part 2: Host Application
Now I need another application which will listen to request from clients. In this sample I 'm going to create a console application. First I have to add a reference to System.RunTime.Remoting. Then I have to prepare a communication line between clients and server. To do this you can use a TCP or HTTP channel. Like this:

HttpChannel channel = new HttpChannel(1234);
ChannelServices.RegisterChannel(channel);

Then you have register the remotable types you want to prepare. As I said before you can choose with activation you want to use. If you want to have Server Activation use this line of code:

RemotingConfiguration.RegisterWellKnownServiceType(typeof(MyRemotableType),"RemotingTest.soap", WellKnownObjectMode.Singleton);
Console.WriteLine("Remote server started ...\r\nPress enter to stop");
Console.ReadLine();

Notice that in line above I used the Singleton but you can change it to SingleCall, also.You can also use RegisterActivatedServiceType . Notice that here in server application I used ReigsterXXXXServicesType
but in the client side you have to use RegisterXXXXClientType. And I also passed a name for this channel " RemotingTest.soap", this name is used to find the remote channel.

Part 3: Client Application
Now I want to use MyRemotableType and create instance from that but as a remote object. To do this first I add a reference to my MyRemotableTypes.dll. The I have to set the channel in my client application. I do this by using the RegisterWellKnownClientType method of RemotingConfiguration, as I said before.

RemotingConfiguration.RegisterWellKnownClientType(typeof(MyRemotableType),"http://RemoteServerName/RemotingTest.soap");

But notice that you give the type you want to use by remoting and also the url of remote server as parameters.
Now try to create some objects from the MyRemotableType.

MyRemotableType t = new MyRemotableType();
t.AddNumbers(10,10);
Console.WriteLine(t.CaldSum(10,10));

Part 4: Test the Applications
Now for testing the application, first run the Server Application,then while the server is running start the client application. And see the result.

As you may see, you will get just one line printed in client :

Sum is: 20

But in server side you got two printed line:
A New MarshalByRefObject created
ُS um is: 20

It means that you the object is created on server and the first method call is Writing to Console of server, but the result of method is accessible in client.

It will discuss more about remoting in my next posts.
You can download the sample code at:
http://www.tabatabaei.info/csharpsamples/firstremoting.rar

Service Controller Sample

In this sample I've used the ServiceController class to view services installed on local or any machine.
You can download the source code here:
http://www.tabatabaei.info/csharpsamples/serviceController.rar

Please let me know if there was any question.

Windows Service Applications

In some cases you may want to have an application which is performing since the computer has been turned on. For instance consider an application which is logging changes in an specific directory in your server, or you might think about Anti Viruses or any other application like that.

Windows Services a kind of windows application without any user interface, which is working in background of your system. In many situation you may want to have an application which is working on your system, event before any user has been logged in.

There is a class names ServiceBase in System.ServiceProcess namespace which has to be derived if you want to have your own Windows Service application. The ServiceBase classs has OnStart() method which will occur when the service has been started using SCM (Service Control Manager) which is accessible by Services icon on Administrative Tools of Control Panel. You can override the OnStart() method for doing any special task in your service. You can also stop your service tasks by overriding the OnStop() method of ServiceBase.

Consider that every service class needs an Service Installer to install the service. So for creating the service installer just goto design mode of your service class and Right Click on it and then click on Add Installer then you will see that a new class has been added to your project. Consider that your services will be run with an specific User of system, to change this behavior you have to change the Account property of ServiceProcessIntaller instance in the new added class to LocalSystem. In the next post I will talk more about other accounts and properties of this class.

َFor running a service you SCM first you have to install. To achieve this goal you can use the InstallUtil application with your assembly (the exe file) passed as parameter. You may also want to uninstall a service which can be done by passing /U at the end of InstallUtil.

I've prepared a sample which will log all the changes in a specified directory within the configuration file. The log file path is also can be set within the configuration file.

You can download the source code here:
http://www.tabatabaei.info/csharpsamples/systemwatcher.rar