8 The C Server Back-end
8.1 Introduction
With the option
{be, c_server}
the IDL Compiler generates C server skeletons according to the IDL to C mapping, on top of the Erlang distribution and gen_server protocols.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
erl_interface
functions for defining the hidden node and for establishing connections to other Erlang nodes.8.2 Generated Stub Files
The generated stub files are:
- For each IDL interface, a C source file, the name of which is
<Scoped Interface Name>__s.c
. Each operation of the IDL interface is mapped to a C function (with scoped name) in that file;
- C source files that contain functions for type conversion, memory allocation, and data encoding/decoding;
- C header files that contain function prototypes and type definitions.
All C functions are exported (i.e. not declared static).
8.3 C Skeleton Functions
For each IDL operation a C skeleton function is generated, the prototype of which is
int <Scoped Function Name>__exec(<Interface Object> oe_obj, CORBA_Environment *oe_env)
, where<Interface Object>
, andCORBA_Environment
are of the same type as for the generated C client stubs code.Each
<Scoped Function Name>__exec()
function calls the call-back function
<Scoped Function Name>_rs* <Scoped Function Name>__cb(<Interface Object> oe_obj, <Parameters>, CORBA_Environment *oe_env)
where the arguments are of the same type as those generated for C client stubs.
The return value
<Scoped Function Name>_rs*
is a pointer to a function with the same signature as the call-back function<Scoped Function Name>_cb
, and is called after the call-back function has been evaluated (provided that the pointer is not equal toNULL
).8.4 The Server Loop
The developer has to implement code for establishing connections with other Erlang nodes, code for call-back functions and restore functions.
In addition, the developer also has to implement code for a server loop, that receives messages and calls the relevant
__exec
function. For that purpose the IC library functionoe_server_receive()
function can be used.8.5 Generating, Compiling and Linking
To generate the C server skeletons type the following in an appropriate shell:
erlc -I ICROOT/include "+{be, c_server}" File.idl
,where
ICROOT
is the root of the IC application. The-I ICROOT/include
is only needed ifFile.idl
refers toerlang.idl
.When compiling a generated C skeleton file, the directories
ICROOT/include
andEICROOT/include
, have to be specified as include directories, whereEIROOT
is the root directory of the Erl_interface application.When linking object files the
EIROOT/lib
andICROOT/priv/lib
directories have to be specified.8.6 An Example
In this example the IDL specification file "random.idl" is used for generating C server skeletons (the file is contained in the IC
/examples/c-server
directory):module rmod { interface random { double produce(); oneway void init(in long seed1, in long seed2, in long seed3); }; };Generate the C server skeletons:
erlc '+{be, c_server}' random.idl Erlang IDL compiler version X.Y.ZSix files are generated.
Compile the C server skeletons:
Please read the
ReadMe
file att theexamples/c-server
directory.In the same directory you can find all the code for this example. In particular you will find the
server.c
file that contains all the additional code that must be written to obtain a complete server.In the
examples/c-server
directory you will also find source code for an Erlang client, which can be used for testing the C server.