Integrating .Net with Erlang, part 1

So, you can integrate Java with Erlang, using the jinterface code supplied as part of the standard Erlang distribution. It's Java, so can we do this with .Net?

Let's start with J#. We set up the erlang source

-module(mathserver).
-export([start/0, add/2]).

start() ->
   Pid = spawn(fun() -> loop() end),
   register(mathserver, Pid).

loop() ->
   receive
      {From, {add, First, Second}} ->
        From ! {mathserver, First + Second},
        loop()
   end.

add(First, Second) ->
   mathserver ! {self(), {add, First, Second}},
   receive
      {mathserver, Reply} -> Reply
   end.

and test it with

>erl -name servernode@chloe.ravnaandtines.com -setcookie cookie
Eshell V5.6  (abort with ^G)
(servernode@chloe.ravnaandtines.com)1> node().
'servernode@chloe.ravnaandtines.com'
(servernode@chloe.ravnaandtines.com)2> pwd().
jinterface          mathserver.erl
ok
(servernode@chloe.ravnaandtines.com)3> c(mathserver).
l{ok,mathserver}
(servernode@chloe.ravnaandtines.com)4> s().
jinterface          mathserver.beam     mathserver.erl
ok
(servernode@chloe.ravnaandtines.com)5> mathserver:start().
true
(servernode@chloe.ravnaandtines.com)6> mathserver:add(1,2).
3
(servernode@chloe.ravnaandtines.com)7>

Now fire up Visual Studio, and create a J# class library project. Add existing items to copy the jinterface code into the project, and build it.

Cannot find type 'java.lang.ref.WeakReference'

Well, that's not too bad. Give it a stub, and build again:

package java.lang.ref;
import System.*;

public class WeakReference extends System.WeakReference
{
    public WeakReference()
    {
    }
}

gives us

error VJS1227: Cannot find constructor 'java.lang.ref.WeakReference(com.ericsson.otp.erlang.OtpMbox)'
error VJS1223: Cannot find method 'get()' in 'java.lang.ref.WeakReference'

So give it what it needs:

package java.lang.ref;
import System.*;

public class WeakReference extends System.WeakReference
{
    public WeakReference(Object o)
    {
        super(o);
    }
    public Object get()
    {
        try
        {
            return this.get_Target();
        }
        catch (InvalidOperationException ioe)
        {
            return null;
        }
    }
}

And it builds. Now put in the driver program:

import com.ericsson.otp.erlang.*;

public class ClientNode
{

    public static void main(String[] _args) throws Exception
    {

        OtpSelf cNode = new OtpSelf("clientnode", "cookie");
        OtpPeer sNode = new OtpPeer("servernode"+"@"+"chloe.ravnaandtines.com");
        OtpConnection connection = cNode.connect(sNode);

        OtpErlangObject[] args = new OtpErlangObject[]{
            new OtpErlangLong(1), new OtpErlangLong(2)};
        connection.sendRPC("mathserver", "add", args);
        OtpErlangLong sum = (OtpErlangLong)connection.receiveRPC();
        if (sum.intValue() != 3)
        {
                throw new IllegalStateException("Assertion failed, returned = " + sum.intValue());
        }
        System.out.println("OK!");

    }

}

Now, run that and get:

OK!

So, we have first light!

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