9 Orber Stubs/Skeletons

9.1 Orber Stubs and Skeletons Description

This example describes the API and behavior of Orber stubs and skeletons.

Server Start

Orber servers can be started in several ways. The chosen start functions determines how the server can be accessed and its behavior.

Using Module_Interface:oe_create() or oe_create_link():

• No initial data can be passed.
• Cannot be used as a supervisor child start function.
• Only accessible through the object reference returned by the start function. The object reference is no longer valid if the server dies and is restarted.

Using Module_Interface:oe_create(Env) or oe_create_link(Env):

• Initial data can be passed using Env.
• Cannot be used as a supervisor child start function.
• Only accessible through the object reference returned by the start function. The object reference is no longer valid if the server dies and is restarted.

Using Module_Interface:oe_create(Env, Options):

• Initial data can be passed using Env.
• Cannot be used as a supervisor child start function.
• Accessible through the object reference returned by the start function. If the option {regname, RegName} is used the object reference stays valid even if the server has been restarted.
• If the options {persistent, true} and {regname, {global, Name}} is used, the result from an object invocation will be the exception 'OBJECT_NOT_EXIST' only if the object has terminated with reason normal or shutdown. If the object is in the process of restarting, the result will be {error, Reason} or a system exception is raised.
• The option {pseudo, true} makes it possible to start create non-server objects. There are, however, some limitations, which are further described in the Pseudo objects section.

Using Module_Interface:oe_create_link(Env, Options):

• Initial data can be passed using Env.
• Can be used as a supervisor child start function if the option {sup_child, true} used.
• Accessible through the object reference returned by the start function. If the option {regname, RegName} is used the object reference stays valid even if the server has been restarted.
• If the options {persistent, true} and {regname, {global, Name}} is used, the result from an object invocation will be the exception 'OBJECT_NOT_EXIST' only if the object has terminated with reason normal or shutdown. If the object is in the process of restarting, the result will be {error, Reason} or a system exception is raised.
• For starting a server as a supervisor child you should use the options [{persistent, true}, {regname, {global, Name}}, {sup_child, true}] and of type transient. This configuration allows you to delegate restarts to the supervisor and still be able to use the same object reference and be able to see if the server is permanently terminated. Please note you must use supervisor/stdlib-1.7 or later and that the it returns {ok, Pid, Object} instead of just Object.
• Using the option {pseudo, true} have the same effect as using oe_create/2.

Pseudo Objects

This section describes Orber pseudo objects.

The Orber stub can be used to start a pseudo object, which will create a non-server implementation. A pseudo object introduce some limitations:

• The functions oe_create_link/2 is equal to oe_create/2, i.e., no link can or will be created.
• The BIF:s self() and process_flag(trap_exit,true) behaves incorrectly.
• The IC option {{impl, "M::I"}, "other_impl"} has no effect. The call-back functions must be implemented in a file called M_I_impl.erl
• The call-back functions must be implemented as if the IC option {this, "M::I"} was used.
• The gen_server State changes have no effect. The user can provide information via the Env start parameter and the State returned from init/2 will be the State passed in following invocations.
• The server reply Timeout has no effect.
• The compile option from has no effect.
• The option {pseudo, true} overrides all other start options.
• Only the functions, besides own definitions, init/2 (called via oe_create*/2) and terminate/2 (called via corba:dispose/1) must be implemented.

By adopting the rules for pseudo objects described above we can use oe_create/2 to create server or pseudo objects, by excluding or including the option {pseudo, true}, without changing the call-back module.

To create a pseudo object do the following:

fingolfin 127> erl 
Erlang (BEAM) emulator version 4.9
 
Eshell V4.9  (abort with ^G)
1> ic:gen(myDefinition, [{this, "MyModule::MyInterface"}]).
Erlang IDL compiler version 20
ok
2> make:all().
Recompile: oe_MyDefinition
Recompile: MyModule_MyInterface
Recompile: MyModule_MyInterface_impl
up_to_date
3> PseudoObj = MyModule_MyInterface:oe_create(Env, [{pseudo, true}]).
      

The call-back functions must be implemented as MyFunction(OE_THIS, State, Args), and called by MyModule_MyInterface:MyFunction(PseudoObj, Args).

Call-back Module

This section provides an example of how a call-back module may be implemented.

%%%-----------------------------------------------------------
%%% File    : Module_Interface_impl.erl
%%% Author  : 
%%% Purpose : 
%%% Created : 
%%%-----------------------------------------------------------
 
-module('Module_Interface_impl').
 
%%--------------- INCLUDES -----------------------------------
-include_lib("orber/include/corba.hrl").
-include_lib(".. ..").
 
%%--------------- EXPORTS-------------------------------------
%% Arity depends on IC configuration parameters and the IDL
%% specification.
-export([own_function/X]).
 
 
%%--------------- gen_server specific ------------------------
-export([init/1, terminate/2, code_change/3, handle_info/2]).
 
%%------------------------------------------------------------
%% function : server specific
%%------------------------------------------------------------
init(InitialData) ->
    %% 'trap_exit' optional (have no effect if pseudo object).
    process_flag(trap_exit,true),

    %%--- Possible replies ---
    %% Reply and await next request
    {ok, State}.

    %% Reply and if no more requests within Time the special 
    %% timeout message should be handled in the 
    %% Module_Interface_impl:handle_info/2 call-back function (use the 
    %% IC option {{handle_info, "Module::Interface"}, true}).
    {ok, State, Timeout} 

    %% Return ignore in order to inform the parent, especially if it is a 
    %% supervisor, that the server, as an example, did not start in 
    %% accordance with the configuration data. 
    ignore 
    %% If the initializing procedure fails, the reason 
    %% is supplied as StopReason.
    {stop, StopReason}

terminate(Reason, State) ->
    ok.

code_change(OldVsn, State, Extra) ->
    {ok, NewState}.

%% If use IC option {{handle_info, "Module::Interface"}, true}. 
%% (have no effect if pseudo object).
handle_info(Info, State) ->
    %%--- Possible replies ---
    %% Await the next invocation.
    {noreply, State}.
    %% Stop with Reason.
    {stop, Reason, State}.

%%--- two-way ------------------------------------------------
%% If use IC option {this, "Module:Interface"} 
%% (Required for pseudo objects)
own_function(This, State, .. Arguments ..) ->
%% IC options this and from
own_function(This, From, State, .. Arguments ..) ->
%% IC option from
own_function(From, State, .. Arguments ..) ->
    %% Send explicit reply to client.
    corba:reply(From, Reply),
    %%--- Possible replies ---
    {noreply, State}
    {noreply, State, Timeout}

 
%% If not use IC option {this, "Module:Interface"}
own_function(State, .. Arguments ..) ->
    %%--- Possible replies ---
    %% Reply and await next request
    {reply, Reply, State}

    %% Reply and if no more requests within Time the special 
    %% timeout message should be handled in the 
    %% Module_Interface_impl:handle_info/2 call-back function (use the
    %% IC option {{handle_info, "Module::Interface"}, true}).
    {reply, Reply, State, Timeout}

    %% Stop the server and send Reply to invoking object.
    {stop, StopReason, Reply, State}

    %% Stop the server and send no reply to invoking object.
    {stop, StopReason, State}

    %% Raise exception. Any changes to the internal State is lost.
    corba:raise(Exception).

%%--- one-way ------------------------------------------------
%% If use IC option {this, "Module:Interface"}
%% (Required for pseudo objects)
own_function(This, State, .. Arguments ..) ->

%% If not use IC option {this, "Module:Interface"}
own_function(State, .. Arguments ..) ->
    %%--- Possible results ---
    {noreply, State}

    %% Release and if no more requests within Time the special 
    %% timeout message should be handled in the 
    %% Module_Interface_impl:handle_info/2 call-back function (use the
    %%  IC option {{handle_info, "Module::Interface"}, true}).
    {noreply, State, Timeout}

    %% Stop the server with StopReason.
    {stop, StopReason, State}

%%--------------- END OF MODULE ------------------------------