[Ericsson AB]

9 Orber Examples

9.1 A Tutorial on How to Create a SimpleSservice

9.1.1 Interface Design

This example uses a very simple stack server. The specification contains two interfaces: the first is the Stack itself and the other is the StackFactory which is used to create new stacks. The specification is in the file stack.idl.

#ifndef _STACK_IDL
#define _STACK_IDL

module StackModule {
  
  exception EmptyStack {};

  interface Stack {

    long pop() raises(StackModule::EmptyStack);

    void push(in long value);

    void empty();

  };

  interface StackFactory {

    StackModule::Stack create_stack();
    void destroy_stack(in StackModule::Stack s);

  };

};

#endif

9.1.2 Generating Erlang Code

Run the IDL compiler on this file by calling the ic:gen/1 function

        1> ic:gen("stack").
      

This will produce the client stub and server skeleton. Among other files a stack API module named StackModule_Stack.erl will be produced. This will produce among other files a stack API module called StackModule_Stack.erl which contains the client stub and the server skeleton.

9.1.3 Implementation of Interface

After generating the API stubs and the server skeletons it is time to implement the servers and if no special options are sent to the IDl compiler the file name should be <global interface name>_impl.erl, in our case StackModule_Stack_impl.erl.

%% StackModule_Stack_impl example file.

-module('StackModule_Stack_impl').
-include_lib("orber/include/corba.hrl").
-include_lib("orber/examples/Stack/StackModule.hrl").
-export([pop/1, push/2, empty/1, init/1, terminate/2]).


init(_Env) ->
    {ok, []}.

terminate(_From, _Reason) ->
    ok.

push(Stack, Val)  ->
    {reply, ok, [Val | Stack]}.

pop([Val | Stack]) ->
    {reply, Val, Stack};
pop([]) ->
    corba:raise(#'StackModule_EmptyStack'{}).

empty(_) ->
    {reply, ok, []}.


We also have the factory interface which is used to create new stacks and that implementation is in the file StackModule_StackFactory_impl.erl.

%% StackModule_StackFactory_impl example file.

-module('StackModule_StackFactory_impl').
-include_lib("orber/include/corba.hrl").
-export([create_stack/1, destroy_stack/2, init/1, terminate/2]).


init(_Env) ->
    {ok, []}.

terminate(_From, _Reason) ->
    ok.

create_stack(State)  ->
    %% Just a create we don't want a link.
    {reply, 'StackModule_Stack':oe_create(), State}.

destroy_stack(State, Stack)  ->
    {reply, corba:dispose(Stack), State}.

To start the factory server one executes the function StackModule_StackFactory:oe_create/0 which in this example is done in the module stack_factory.erl where the started service is also registered in the name service.

%% stack_factory example file.

-module('stack_factory').
-include_lib("orber/include/corba.hrl").
-include_lib("orber/COSS/CosNaming/CosNaming.hrl").
-include_lib("orber/COSS/CosNaming/lname.hrl").

-export([start/0]).

start() ->
    SFok = 'StackModule_StackFactory':oe_create(),
    NS = corba:resolve_initial_references("NameService"),
    NC = lname_component:set_id(lname_component:create(), "StackFactory"),
    N = lname:insert_component(lname:create(), 1, NC),
    'CosNaming_NamingContext':bind(NS, N, SFok).


9.1.4 Writing a Client in Erlang

At last we will write a client to access our service.

%% stack_client example file.

-module('stack_client').
-include_lib("orber/include/corba.hrl").
-include_lib("orber/COSS/CosNaming/CosNaming.hrl").
-include_lib("orber/COSS/CosNaming/lname.hrl").
 
-export([run/0, run/1]).


run() ->
    NS = corba:resolve_initial_references("NameService"),
    run_1(NS).

run(HostRef) ->
    NS = corba:resolve_initial_references_remote("NameService", HostRef),
    run_1(NS).


run_1(NS) ->
    NC = lname_component:set_id(lname_component:create(), "StackFactory"),
    N = lname:insert_component(lname:create(), 1, NC),
    case catch 'CosNaming_NamingContext':resolve(NS, N) of
        {'EXCEPTION', _E} ->
            io:format("The stack factory server is not registered~n",[]);
        SF ->
            %% Create the stack
            SS = 'StackModule_StackFactory':create_stack(SF),

            %% io:format("SS pid ~w~n",[iop_ior:get_key(SS)]),
            'StackModule_Stack':push(SS, 4),
            'StackModule_Stack':push(SS, 7),
            'StackModule_Stack':push(SS, 1),
            'StackModule_Stack':push(SS, 1),
            Res = 'StackModule_Stack':pop(SS),
            io:format("~w~n", [Res]),
            Res1 = 'StackModule_Stack':pop(SS),
            io:format("~w~n", [Res1]),
            Res2 = 'StackModule_Stack':pop(SS),
            io:format("~w~n", [Res2]),
            Res3 = 'StackModule_Stack':pop(SS),
            io:format("~w~n", [Res3]),

            %% Remove the stack
            'StackModule_StackFactory':destroy_stack(SF, SS)
            
    end.



9.1.5 Writing a Client in Java

To write a Java client for Orber you must have another ORB that uses IIOP for client-server communication and supports a Java language mapping. It must also have support for IDL:CosNaming/NamingContext or IDL:CosNaming/NamingContextExt. If the client ORB support Interoperable Naming Service the Java Client can look like:

/*
 * Stack example using Interoperable Naming Service.
 */

package StackModule;
import org.omg.CORBA.*;
import org.omg.CORBA.SystemException;
import org.omg.CORBA.ORB.*;

public class StackClient 
{
  public static void main(String args[])
    {
      org.omg.CORBA.Object objRef;
      StackFactory sfRef = null;
      Stack sRef = null;
      // The argument can look like
      // "corbaname::host:4001/#StackFactory"
      String corbaName = new String(args[0]);
      try{
          ORB orb = ORB.init(args, null);

          objRef = orb.string_to_object(corbaName);
          sfRef  = StackFactoryHelper.narrow(objRef);
          sRef   = sfRef.create_stack();

          sRef.push(4);
          sRef.push(7);
          sRef.push(1);
          sRef.push(1);
                   
          try{
              System.out.println(sRef.pop());
              System.out.println(sRef.pop());
              System.out.println(sRef.pop());
              System.out.println(sRef.pop());
              // The following operation shall
              // return an EmptyStack exception
              System.out.println(sRef.pop());
            }
          catch(EmptyStack es) {
              System.out.println("Empty stack");
            };

          sfRef.destroy_stack(sRef);
        }
     catch(SystemException se)
       {
         System.out.println("Unexpected exception: " + se.toString());
         return;
       }
    }
}
      

If the Client ORB does not support Interoperable Naming Service, a Java package named Orber is included with our product. It contains just one class, InitialReference which can be used to get the initial reference to Orber's naming service. The Java client will then look like this:

/*
 * Stack example.
 */

package StackModule;
import org.omg.CosNaming.*;
import org.omg.CORBA.*;
import org.omg.CORBA.SystemException;
import org.omg.CORBA.ORB.*;

public class StackClient 
{
  public static void main(String args[])
    {
      NamingContext nsContext;
      org.omg.CORBA.Object objRef;
      StackFactory sfRef = null;
      Stack sRef = null;
      org.omg.CORBA.Object nsRef, initRef;
      NameComponent[] name = new NameComponent[1];
      Orber.InitialReference ir = new Orber.InitialReference();
      Orber.InitialReferences init;
      String srvHost = new String(args[0]);
      Integer srvPort = new Integer(args[1]);

      try
        {
          ORB orb = ORB.init(args, null);

          // Create Initial reference (objectkey "INIT").
           String s = ir.stringified_ior(srvHost, srvPort.intValue());
           initRef = orb.string_to_object(s);
           init = Orber.InitialReferencesHelper.narrow(initRef);

           // Fetch name service reference.
           nsRef = init.get("NameService");
           nsContext = NamingContextHelper.narrow(nsRef);
           // Create a name
           name[0] = new NameComponent("StackFactory", "");

           try
             {
               objRef = nsContext.resolve(name);
             }
           catch(Exception n)
             {
               System.out.println("Unexpected exception: " + n.toString());
               return;
             }      
           
          sfRef = StackFactoryHelper.narrow(objRef);
          sRef = sfRef.create_stack();

          sRef.push(4);
          sRef.push(7);
          sRef.push(1);
          sRef.push(1);
              
          try
            {
              System.out.println(sRef.pop());
              System.out.println(sRef.pop());
              System.out.println(sRef.pop());
              System.out.println(sRef.pop());
              // The following operation shall return an EmptyStack exception
              System.out.println(sRef.pop());
            }
          catch(EmptyStack es)
            {
              System.out.println("Empty stack");
            };

          sfRef.destroy_stack(sRef);

        }
      catch(SystemException se)
        {
          System.out.println("Unexpected exception: " + se.toString());
          return;
        }
    }
}

Note!

If an ORB does not support CosNaming at all the cos_naming.idl file must be compiled and imported.

9.1.6 Building the Example

To build the example for access from a Java client you need a Java enabled ORB. The build log below, using OrbixWeb's IDL compiler, describes the scenario where the Client ORB does not support Naming Service.

fingolfin 127> erl 
Erlang (BEAM) emulator version 4.9
 
Eshell V4.9  (abort with ^G)
1> ic:gen(stack).
Erlang IDL compiler version 20
ok
2> make:all().
Recompile: oe_stack
Recompile: StackModule_StackFactory
Recompile: StackModule_Stack
Recompile: StackModule
Recompile: stack_client
Recompile: stack_factory
Recompile: StackModule_StackFactory_impl
Recompile: StackModule_Stack_impl
up_to_date
3> 
BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
       (v)ersion (k)ill (D)b-tables (d)istribution
a

fingolfin 128> idl stack.idl
fingolfin 129> idl InitialReferences.idl 
fingolfin 130> idl <OTP_INSTALLATIONPATH>/lib/orber-<Orber Version>/COSS/
                   CosNaming/cos_naming.idl 
fingolfin 131> 
fingolfin 132> cd java_output/
fingolfin 133> javac *.java
fingolfin 134> cd CosNaming/
fingolfin 135> javac *.java
fingolfin 136> cd ../_NamingContext/
fingolfin 137> cd javac *.java
fingolfin 138> cd ../../Orber/
fingolfin 139> javac *.java
fingolfin 140> cd ../StackModule/
fingolfin 141> javac *.java
fingolfin 142> cd ../..
fingolfin 143> javac *.java
fingolfin 144> cp StackClient.class java_output/StackModule/.

      

9.1.7 How to Run Everything

Below is a short transcript on how to run Orber. The commands for starting the new socket communication package will not be necessary when it is used as default in OTP R3A. In R2 it is only available unsupported, and without documentation but Orber uses this for better IIOP performance. An example .inetrc can also be found in Orber's example directory and is named inetrc (without the starting .).


fingolfin 143> erl 
Erlang (BEAM) emulator version 4.9
 
Eshell V4.9    (abort with ^G)
1> mnesia:create_schema([]).
ok
2> orber:install([]). 
ok
3> orber:start().             
ok
4> oe_stack:oe_register().     
ok
5> stack_factory:start().
ok
6> stack_client:run().
1
1
7
4
ok
7> 
      

Before testing the Java part of this example generate and compile Java classes for orber/examples/stack.idl, orber/examples/InitialReferences.idl and orber/COSS/CosNaming/cos_naming.idl as seen in the build example. We have tested with OrbixWeb.

To run the Java client use the following command (the second parameter is the port number for the bootstrap port):


fingolfin 38> java StackModule.StackClient fingolfin 4001
[New Connection (fingolfin,4001, null,null,pid=0) ]
[New Connection (fingolfin.du.etx.ericsson.se,4001, null,null,pid=0) ]
1
1
7
4
Empty stack
fingolfin 39> 
      

9.2 A Tutorial on How to Start Orber as Lightweight

9.2.1 Preparation

When starting Erlang the configuration parameter lightweight must be used. The value is set to a list of remote modifiers, equal to the orber:resolve_initial_references_remote/2 argument, i.e., "iiop://host:port". On these given nodes, all necessary oe_X:oe_register() calls must be done before running a Orber lightweight.

Lightweight Orber do not allow us to:

With lightweight Orber we do not:

To be able to start objects we must supply a factory on a non-lightweight node(s) which can start necessary objects. One way to accomplish this is:

smaug 125> erl -orber domain "ORBER_MAIN"
Erlang (BEAM) emulator version 4.9
 
Eshell V4.9    (abort with ^G)
1> mnesia:create_schema([]).
2> orber:install([]). 
3> orber:start().             
4> oe_MyFactory:oe_register().
5> oe_MyObjects:oe_register().  %% Do this for all objects necessary.
6> Factory=MyFactory_Creater:oe_create().
7> NS=orber:resolve_initial_references("NameService").
8> NC=lname_component:set_id(lname_component:create(), "myFactory").
9> N =lname:insert_component(lname:create(), 1, NC).
10> 'CosNaming_NamingContext':bind(NS, N, Factory)).
      

Now we have a factory we can access from, hence, we can now start a lightweight Orber:

fingolfin 14> erl -orber lightweight [\"iiop://host1:port\", 
                                      \"iiop://host2:port\"]
                  -orber domain \"ORBER_LIGHT\"
Erlang (BEAM) emulator version 4.9
 
Eshell V4.9    (abort with ^G)
1> orber:start_lightweight().             
2> Fac=corba:string_to_object("corbaname::Host:Port/NameService#myFactory"), 
3> Obj=MyFactory_Creater:MyObject(Fac, Args).
4> MyObject:myFunction(Obj,Args2).
      

It is not necessary to start both Orber types using the configuration parameter domain, but at least one of them.


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