Passing proxy vs. passing identity in Glacier2

I noticed that in Ice-3.5.1/py/demo/Glacier2/callback the RPC call passes the callback receiver proxy to the server, while in Ice-3.5.1/py/demo/Ice/bidir it passes only the identity and the callback receiver proxy is created from the identity.

I tried to change the Glacier2 callback example to pass the callback receiver's identity like in bidir, however, that makes both client, router and server crash without error messages. Do you know why?

Part changed in client:

class Client(Glacier2.Application):
def createSession(self):
session = None
try:
session = self.router().createSession('', '')
except Glacier2.PermissionDeniedException as ex:
print("permission denied:\n" + ex.reason)
except Glacier2.CannotCreateSessionException as ex:
print("cannot create session:\n" + ex.reason)
return session

def runWithSession(self, args):
if len(args) > 1:
print(self.appName() + ": too many arguments")
return 1

# Create proxy for callback object in server.
base = self.communicator().propertyToProxy('Callback.Proxy')
twoway = Demo.CallbackPrx.checkedCast(base)

# Create callback receiver object.
callbackReceiverIdent = self.createCallbackIdentity("callbackReceiver")
self.objectAdapter().add(CallbackReceiverI(), callbackReceiverIdent)

# Create callback receiver proxy to be sent to server.
twowayR = Demo.CallbackReceiverPrx.uncheckedCast(self.objectAdapter().createProxy(callbackReceiverIdent))

# Initiate callback from server, passing callback receiver identity.
twoway.initiateCallback(callbackReceiverIdent)

return 0


Part changed in server:

class CallbackI(Demo.Callback):
def __init__(self, communicator):
self._communicator = communicator

def initiateCallback(self, ident, current=None):
print("adding client `" + self._communicator.identityToString(ident) + "'")
client = Demo.CallbackReceiverPrx.uncheckedCast(current.con.createProxy(ident))
try:
client.callback()
except:
traceback.print_exc()


Changed interface:

#pragma once

#include <Ice/Identity.ice>

module Demo
{

interface CallbackReceiver
{
void callback();
};

interface Callback
{
void initiateCallback(Ice::Identity ident);
void shutdown();
};

};