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<chapter>
  <header>
    <copyright>
      <year>1998</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
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      distributed under the License is distributed on an "AS IS" BASIS,
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    <title>The C Server Back-end</title>
    <prepared></prepared>
    <docno></docno>
    <date>2004-01-14</date>
    <rev>C</rev>
    <file>ch_c_server.xml</file>
  </header>

  <section>
    <title>Introduction</title>
    <p>With the option <c>{be, c_server}</c> the IDL Compiler generates
      C server skeletons according to the IDL to C mapping, on top of
      the Erlang distribution and gen_server protocols.</p>
    <p>The developer has to write additional code, that together with
      the generated C server skeletons, form a hidden Erlang
      node. That additional code contains implementations of call-back
      functions that implement the true server functionality, and also
      code uses <c>erl_interface</c> functions for defining the hidden
      node and for establishing connections to other Erlang nodes.</p>
  </section>

  <section>
    <title>Generated Stub Files</title>
    <p>The generated stub files are:</p>
    <list type="bulleted">
      <item>
        <p>For each IDL interface, a C source file, the name of which
          is <c><![CDATA[<Scoped Interface Name>__s.c]]></c>. Each operation of the
          IDL interface is mapped to a C function (with scoped name)
          in that file;</p>
      </item>
      <item>
        <p>C source files that contain functions for type conversion,
          memory allocation, and data encoding/decoding;</p>
      </item>
      <item>
        <p>C header files that contain function prototypes and type
          definitions.</p>
      </item>
    </list>
    <p>All C functions are exported (i.e. not declared static).</p>
  </section>

  <section>
    <title>C Skeleton Functions</title>
    <p>For each IDL operation a C skeleton function is generated, the
      prototype of which is <c><![CDATA[int <Scoped Function Name>__exec(<Interface Object> oe_obj, CORBA_Environment *oe_env)]]></c>, where <c><![CDATA[<Interface Object>]]></c>, and
      <c>CORBA_Environment</c> are of the same type as for the
      generated C client stubs code.</p>
    <p>Each <c><![CDATA[<Scoped Function Name>__exec()]]></c> function calls the
      call-back function</p>
    <p><c><![CDATA[<Scoped Function Name>_rs* <Scoped Function Name>__cb(<Interface Object> oe_obj, <Parameters>, CORBA_Environment *oe_env)]]></c></p>
    <p>where the arguments are of the same type as those generated for
      C client stubs. </p>
    <p>The return value <c><![CDATA[<Scoped Function Name>_rs* ]]></c> is a pointer
      to a function with the same signature as the call-back function
      <c><![CDATA[<Scoped Function Name>_cb]]></c>, and is called after the call-back
      function has been evaluated (provided that the pointer is not equal
      to <c>NULL</c>). </p>
  </section>

  <section>
    <title>The Server Loop</title>
    <p>The developer has to implement code for establishing connections
      with other Erlang nodes, code for call-back functions and restore
      functions. </p>
    <p></p>
    <p>In addition, the developer also has to implement code for a
      server loop, that receives messages and calls the relevant
      <c>__exec</c> function. For that purpose the IC library function
      <c>oe_server_receive()</c> function can be used.</p>
  </section>

  <section>
    <title>Generating, Compiling and Linking</title>
    <p>To generate the C server skeletons type the following in an
      appropriate shell:</p>
    <p><c>erlc -I ICROOT/include "+{be, c_server}"  File.idl</c>,</p>
    <p>where <c>ICROOT</c> is the root of the IC application. The
      <c>-I ICROOT/include</c> is only needed if <c>File.idl</c>
      refers to <c>erlang.idl</c>.</p>
    <p>When compiling a generated C skeleton file, the directories
      <c>ICROOT/include</c> and <c>EICROOT/include</c>, have to be
      specified as include directories, where <c>EIROOT</c> is the
      root directory of the Erl_interface application.</p>
    <p>When linking object files the <c>EIROOT/lib</c> and
      <c>ICROOT/priv/lib</c> directories have to be specified. </p>
  </section>

  <section>
    <title>An Example</title>
    <p>In this example the IDL specification file "random.idl" is used
      for generating C server skeletons (the file is contained in the IC
      <c>/examples/c-server</c> directory):</p>
    <code type="none">
module rmod {
 
  interface random {
 
    double produce();
 
    oneway void init(in long seed1, in long seed2, in long seed3);
 
  };
 
};        </code>
    <p>Generate the C server skeletons:</p>
    <code type="none">
erlc '+{be, c_server}' random.idl
Erlang IDL compiler version X.Y.Z        </code>
    <p>Six files are generated. </p>
    <p>Compile the C server skeletons:</p>
    <p>Please read the <c>ReadMe</c> file in the
      <c>examples/c-server</c> directory.</p>
    <p>In the same directory you can find all the code for this
      example.  In particular you will find the <c>server.c</c> file
      that contains all the additional code that must be written to
      obtain a complete server.</p>
    <p>In the <c>examples/c-server</c> directory you will also find
      source code for an Erlang client, which can be used for testing
      the C server.</p>
  </section>
</chapter>


