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This page shows how to create an Ice application with C#.

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Compiling a Slice Definition for C#

The first step in creating our C# application is to compile our Slice definition to generate C# proxies and skeletons. You can compile the definition as follows:

> mkdir generated
> slice2cs --output-dir generated Printer.ice

The --output-dir option instructs the compiler to place the generated files into the generated directory. This avoids cluttering the working directory with the generated files. The slice2cs compiler produces a single source file, Printer.cs, from this definition. The exact contents of this file do not concern us for now — it contains the generated code that corresponds to the Printer interface we defined in Printer.ice.

Writing and Compiling a Server in C#

To implement our Printer interface, we must create a servant class. By convention, a servant class uses the name of its interface with an I-suffix, so our servant class is called PrinterI and placed into a source file Server.cs:

C#
using System;

public class PrinterI : Demo.PrinterDisp_
{
    public override void printString(string s, Ice.Current current)
    {
        Console.WriteLine(s);
    }
}

The PrinterI class inherits from a base class called PrinterDisp_, which is generated by the slice2cs compiler. The base class is abstract and contains a printString method that accepts a string for the printer to print and a parameter of type Ice.Current. (For now we will ignore the Ice.Current parameter.) Our implementation of the printString method simply writes its argument to the terminal.

The remainder of the server code follows in Server.cs and is shown in full here:

C#
public class Server
{
    public static int Main(string[] args)
    {
        try
        {
            using(Ice.Communicator communicator = Ice.Util.initialize(ref args)) 
            {
                communicator = Ice.Util.initialize(ref args);
                Ice.ObjectAdapter adapter = communicator.createObjectAdapterWithEndpoints("SimplePrinterAdapter", "default -p 10000");
                Ice.Object obj = new PrinterI();
                adapter.add(obj, ic.stringToIdentity("SimplePrinter"));
                adapter.activate();
                ic.waitForShutdown();
            }
        } 
        catch(Exception e)
        {
            Console.Error.WriteLine(e);
	        return 1;
        }
        return 0;
    }
}

The body of Main contains a try block in which we place all the server code, followed by a catch block. The catch block catches all exceptions that may be thrown by the code; the intent is that, if the code encounters an unexpected run-time exception anywhere, the stack is unwound all the way back to Main, which prints the exception and then returns failure to the operating system.

The Ice.Communicator object implements IDisposable, which allows us to use the using statement for the initialization of the Ice.Communicator object. This ensures the communicator destroy method is called when the using block goes out of scope. Doing this is essential in order to correctly finalize the Ice run time.

Failure to call destroy on the communicator before the program exits results in undefined behavior.

The body of our try block contains the actual server code.

The code goes through the following steps:

  1. We initialize the Ice run time by calling Ice.Util.initialize. (We pass args to this call because the server may have command-line arguments that are of interest to the run time; for this example, the server does not require any command-line arguments.) The call to initialize returns an Ice.Communicator reference, which is the main object in the Ice run time.
  2. We create an object adapter by calling createObjectAdapterWithEndpoints on the Communicator instance. The arguments we pass are "SimplePrinterAdapter" (which is the name of the adapter) and "default -p 10000", which instructs the adapter to listen for incoming requests using the default protocol (TCP/IP) at port number 10000.
  3. At this point, the server-side run time is initialized and we create a servant for our Printer interface by instantiating a PrinterI object.
  4. We inform the object adapter of the presence of a new servant by calling add on the adapter; the arguments to add are the servant we have just instantiated, plus an identifier. In this case, the string "SimplePrinter" is the name of the Ice object. (If we had multiple printers, each would have a different name or, more correctly, a different object identity.)
  5. Next, we activate the adapter by calling its activate method. (The adapter is initially created in a holding state; this is useful if we have many servants that share the same adapter and do not want requests to be processed until after all the servants have been instantiated.)
  6. Finally, we call waitForShutdown. This call suspends the calling thread until the server implementation terminates, either by making a call to shut down the run time, or in response to a signal. (For now, we will simply interrupt the server on the command line when we no longer need it.)

Note that, even though there is quite a bit of code here, that code is essentially the same for all servers. You can put that code into a helper class and, thereafter, will not have to bother with it again. (Ice provides such a helper class, called Ice.Application.) As far as actual application code is concerned, the server contains only a few lines: seven lines for the definition of the PrinterI class, plus three lines to instantiate a PrinterI object and register it with the object adapter.

We can compile the server code as follows:

$ csc /reference:Ice.dll /lib:%ICE_HOME%\Assemblies Server.cs generated\Printer.cs

This compiles both our application code and the code that was generated by the Slice compiler. We assume that the ICE_HOME environment variable is set to the top-level directory containing the Ice run time. (For example, if you have installed Ice in C:\Ice, set ICE_HOME to that path.)

Writing and Compiling a Client in C#

The client code, in Client.cs, looks very similar to the server.

Here it is in full:

C#
using System;
using Demo;

public class Client
{
    public static int Main(string[] args)
    {
        try
        {
            using(Ice.Communicator communicator = Ice.Util.initialize(ref args))
            {
                Ice.ObjectPrx obj = communicator.stringToProxy("SimplePrinter:default -p 10000");
                PrinterPrx printer = PrinterPrxHelper.checkedCast(obj);
                if(printer == null)
                {
                    throw new ApplicationException("Invalid proxy");
                }

                printer.printString("Hello World!");
            }
        } 
        catch(Exception e)
        {
            Console.Error.WriteLine(e);
            return 1;
        }
		return 0;
    }
}

Note that the overall code layout is the same as for the server: we use the same try and catch blocks to deal with errors. The code in the try block does the following:

  1. As for the server, we initialize the Ice run time by calling Ice.Util.initialize within the using statement
  2. The next step is to obtain a proxy for the remote printer. We create a proxy by calling stringToProxy on the communicator, with the string "SimplePrinter:default -p 10000". Note that the string contains the object identity and the port number that were used by the server. (Obviously, hard-coding object identities and port numbers into our applications is a bad idea, but it will do for now; we will see more architecturally sound ways of doing this when we discuss IceGrid.
  3. The proxy returned by stringToProxy is of type Ice.ObjectPrx, which is at the root of the inheritance tree for interfaces and classes. But to actually talk to our printer, we need a proxy for a Printer interface, not an Object interface. To do this, we need to do a down-cast by calling PrinterPrxHelper.checkedCast. A checked cast sends a message to the server, effectively asking "is this a proxy for a Printer interface?" If so, the call returns a proxy of type Demo::Printer; otherwise, if the proxy denotes an interface of some other type, the call returns null.
  4. We test that the down-cast succeeded and, if not, throw an error message that terminates the client.
  5. We now have a live proxy in our address space and can call the printString method, passing it the time-honored "Hello World!" string. The server prints that string on its terminal.

Compiling the client looks much the same as for the server:

$ csc /reference:Ice.dll /lib:%ICE_HOME%\Assemblies Client.cs generated\Printer.cs

Running Client and Server in C#

To run client and server, we first start the server in a separate window:

$ server.exe

At this point, we won't see anything because the server simply waits for a client to connect to it. We run the client in a different window:

$ client.exe
$

The client runs and exits without producing any output; however, in the server window, we see the "Hello World!" that is produced by the printer. To get rid of the server, we interrupt it on the command line for now. (We will see cleaner ways to terminate a server in our discussion of Ice.Application.)

If anything goes wrong, the client will print an error message. For example, if we run the client without having first started the server, we get something like the following:

Ice.ConnectionRefusedException
    error = 0
   at IceInternal.ProxyFactory.checkRetryAfterException(LocalException ex, Reference ref, Int32 cnt)
   at Ice.ObjectPrxHelperBase.handleException__(ObjectDel_ delegate, LocalException ex, Int32 cnt)
   at Ice.ObjectPrxHelperBase.ice_isA(String id__, Dictionary`2 context__, Boolean explicitContext__)
   at Ice.ObjectPrxHelperBase.ice_isA(String id__)
   at Demo.PrinterPrxHelper.checkedCast(ObjectPrx b)
   at Client.Main(String[] args)
Caused by: System.ComponentModel.Win32Exception: No connection could be made because the target machine actively refused
 it

Note that, to successfully run client and server, the C# run time must be able to locate the Ice.dll library. (Under Windows, one way to ensure this is to copy the library into the current directory. Please consult the documentation for your C# run time to see how it locates libraries.)

See Also

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