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<h1>9 Orber Stubs/Skeletons</h1>
<h3><a name="id82459">9.1
Orber Stubs and Skeletons Description</a></h3>
<p>This example describes the API and behavior of Orber stubs and skeletons.
</p>
<h4>Server Start</h4>
<p>Orber servers can be started in several ways. The chosen start functions determines
how the server can be accessed and its behavior.
</p>
<p>Using <span class="code">Module_Interface:oe_create()</span> or <span class="code">oe_create_link()</span>:
</p>
<ul>
<li>No initial data can be passed.</li>
<li>Cannot be used as a supervisor child start function.</li>
<li>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The object reference is no longer valid if the server dies and is restarted.</li>
</ul>
<p>Using <span class="code">Module_Interface:oe_create(Env)</span> or <span class="code">oe_create_link(Env)</span>:</p>
<ul>
<li>Initial data can be passed using <span class="code">Env</span>.</li>
<li>Cannot be used as a supervisor child start function.</li>
<li>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The object reference is no longer valid if the server dies and is restarted.</li>
</ul>
<p>Using <span class="code">Module_Interface:oe_create(Env, Options)</span>:</p>
<ul>
<li>Initial data can be passed using <span class="code">Env</span>.</li>
<li>Cannot be used as a supervisor child start function.</li>
<li>Accessible through the object reference returned by the start function. If the option
<span class="code">{regname, RegName}</span> is used the object reference stays valid even if the
server has been restarted.</li>
<li>If the options <span class="code">{persistent, true}</span> and <span class="code">{regname, {global, Name}}</span> is used,
the result from an object invocation will be the exception 'OBJECT_NOT_EXIST'
only if the object has terminated with reason
<span class="code">normal</span> or <span class="code">shutdown</span>. If the object is in the process of restarting, the result
will be <span class="code">{error, Reason}</span> or a system exception is raised.</li>
<li>The option <span class="code">{pseudo, true}</span> makes it possible to start create non-server objects.
There are, however, some limitations, which are further described in the
<span class="code">Pseudo objects</span> section.</li>
</ul>
<p>Using <span class="code">Module_Interface:oe_create_link(Env, Options)</span>:</p>
<ul>
<li>Initial data can be passed using <span class="code">Env</span>.</li>
<li>Can be used as a supervisor child start function if the option <span class="code">{sup_child, true}</span> used.</li>
<li>Accessible through the object reference returned by the start function. If the option
<span class="code">{regname, RegName}</span> is used the object reference stays valid even if the
server has been restarted.</li>
<li>If the options <span class="code">{persistent, true}</span> and <span class="code">{regname, {global, Name}}</span> is used,
the result from an object invocation will be the exception 'OBJECT_NOT_EXIST'
only if the object has terminated with reason
<span class="code">normal</span> or <span class="code">shutdown</span>. If the object is in the process of restarting, the result
will be <span class="code">{error, Reason}</span> or a system exception is raised.</li>
<li>For starting a server as a supervisor child you should use the options
<span class="code">[{persistent, true}, {regname, {global, Name}}, {sup_child, true}]</span> and of type <strong>transient</strong>.
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 <strong>supervisor/stdlib-1.7</strong> or later and that the it returns
<span class="code">{ok, Pid, Object}</span> instead of just <span class="code">Object</span>.</li>
<li>Using the option <span class="code">{pseudo, true}</span> have the same effect as using
<span class="code">oe_create/2</span>.</li>
</ul>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>To avoid flooding Orber with old object references start erlang using the flag
<strong>-orber objectkeys_gc_time Time</strong>, 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 <strong>infinity</strong>. For more information, see the orber and corba documentation.</p>
</p></div>
</div>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>Orber still allow <span class="code">oe_create(Env, {Type,RegName})</span> and <span class="code">oe_create_link(Env, {Type,RegName})</span> to be used,
but may not in future releases.</p>
</p></div>
</div>
<h4>Pseudo Objects</h4>
<p>This section describes Orber pseudo objects.
</p>
<p>The Orber stub can be used to start a <span class="code">pseudo object</span>, which will create a non-server implementation.
A pseudo object introduce some limitations:</p>
<ul>
<li>The functions <span class="code">oe_create_link/2</span> is equal to <span class="code">oe_create/2</span>, i.e.,
no link can or will be created.</li>
<li>The <span class="code">BIF:s self()</span> and <span class="code">process_flag(trap_exit,true)</span> behaves incorrectly.</li>
<li>The <span class="code">IC</span> option <span class="code">{{impl, "M::I"}, "other_impl"}</span> has no effect. The call-back
functions must be implemented in a file called <span class="code">M_I_impl.erl</span>
</li>
<li>The call-back functions must be implemented as if the <span class="code">IC</span> option
<span class="code">{this, "M::I"}</span> was used.</li>
<li>The gen_server <span class="code">State</span> changes have no effect. The user can provide information via
the <span class="code">Env</span> start parameter and the State returned from <span class="code">init/2</span> will be the State
passed in following invocations.</li>
<li>The server reply <span class="code">Timeout</span> has no effect.</li>
<li>The compile option <span class="code">from</span> has no effect.</li>
<li>The option <span class="code">{pseudo, true}</span> overrides all other start options.</li>
<li>Only the functions, besides own definitions, <span class="code">init/2</span> (called via oe_create*/2) and
<span class="code">terminate/2</span> (called via corba:dispose/1) must be implemented.</li>
</ul>
<p>By adopting the rules for <span class="code">pseudo</span> objects described above we can use <span class="code">oe_create/2</span>
to create <span class="code">server</span> or <span class="code">pseudo</span> objects, by excluding or including the
option <span class="code">{pseudo, true}</span>, without changing the call-back module.</p>
<p>To create a pseudo object do the following:</p>
<div class="example"><pre>
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}]).
</pre></div>
<p>The call-back functions must be implemented as <span class="code">MyFunction(OE_THIS, State, Args)</span>,
and called by <span class="code">MyModule_MyInterface:MyFunction(PseudoObj, Args)</span>.</p>
<h4>Call-back Module</h4>
<p>This section provides an example of how a call-back module may be implemented.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Arguments and Replies are determined by the IDL-code and, hence, not
further described here.</p>
</p></div>
</div>
<div class="example"><pre>
%%%-----------------------------------------------------------
%%% 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 ------------------------------
</pre></div>
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