Erlang -- Orber Stubs/Skeletons

orber

User's Guide

Version 3.8.3

- User's Guide
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- Release Notes
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### Chapters

- The Orber Application
  - Top of chapter
  - Content Overview
  - Brief Description of the User's Guide
- Introduction to Orber
  - Top of chapter
  - Overview
- The Orber Application
  - Top of chapter
  - ORB Kernel and IIOP
  - The Object Request Broker (ORB)
  - Internet Inter-Object Protocol (IIOP)
- Interface Repository
  - Top of chapter
  - Interface Repository(IFR)
- Installing Orber
  - Top of chapter
  - Installation Process
  - Configuration
  - Firewall Configuration
  - Interface Configuration
- OMG IDL to Erlang Mapping
  - Top of chapter
  - OMG IDL to Erlang Mapping - Overview
  - OMG IDL Mapping Elements
  - Getting Started
  - Basic OMG IDL Types
  - Template OMG IDL Types and Complex Declarators
  - Constructed OMG IDL Types
  - Scoped Names and Generated Files
  - Typecode, Identity and Name Access Functions
  - References to Constants
  - References to Objects Defined in OMG IDL
  - Exceptions
  - Access to Attributes
  - Invocations of Operations
  - Implementing the DB Application
  - Reserved Compiler Names and Keywords
  - Type Code Representation
- CosNaming Service
  - Top of chapter
  - Overview of the CosNaming Service
  - The Basic Use-cases of the Naming Service
  - Interoperable Naming Service
- How to use security in Orber
  - Top of chapter
  - Security in Orber
- Orber Stubs/Skeletons
  - Top of chapter
  - Orber Stubs and Skeletons Description
- CORBA System and User Defined Exceptions
  - Top of chapter
  - System Exceptions
  - User Defined Exceptions
  - Throwing Exceptions
  - Catching Exceptions
- Orber Interceptors
  - Top of chapter
  - Using Interceptors
  - Interceptor Example
- OrberWeb
  - Top of chapter
  - Using OrberWeb
  - Starting OrberWeb
- Debugging
  - Top of chapter
  - Tools and FAQ

# 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.

Warning

To avoid flooding Orber with old object references start erlang using the flag -orber objectkeys_gc_time Time, which will remove all object references related to servers being dead for Time seconds. To avoid extra overhead, i.e., performing garbage collect if no persistent objects are started, the objectkeys_gc_time default value is infinity. For more information, see the orber and corba documentation.

Warning

Orber still allow oe_create(Env, {Type,RegName}) and oe_create_link(Env, {Type,RegName}) to be used, but may not in future releases.

#### 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.

Note

Arguments and Replies are determined by the IDL-code and, hence, not further described here.

    %%%-----------------------------------------------------------
    %%% 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 ------------------------------