Creating a New Gaudi Service

1. Define the Interface(s)

1. What is this service supposed to do?  Can the tasks be broken down into multiple components (i.e. interfaces)?

2. Define the interface class(es), making sure they derive from Gaudi's IInterface class. (This defines Gaudi mechanism for identifying the interfaces at runtime.)

For each class:

• Define the methods for the interface class.

Note:  This is an abstract class..  you will not actually define the implementation of these methods until you define your new Service class...see the next step.

• Define the name of the ID for this interface:

  // Declaration of the interface ID ( interface id, major version, minor version) 
  static const InterfaceID IID_IFluxSvc(910, 1 , 0); 

The convention is to name the identifier variable as

IID_NameOfInterfaceClass

Note: Each Interface is assigned its own unique ID.  Gaudi has already defined IDs for each of its own interfaces.  You do not want to re-use an existing ID.

2. Define a new class that is derived from Gaudi's Service class and your newly defined Interface class(es).

   This requires defining the initialize( ), finalize( ), and queryInterface( ) methods:

   initialize( )
   	call Service::initialize( ) as the first statement.
   	make a call to setProperties( ) - to access jobOptions for this service
   finalize( )
   	perform any cleanup that is necessary, i.e. free any allocated memory
   queryInterface( )
   	reports the type of  interfaces that a particular service implements.

   Example:

   StatusCode GlastDetSvc::queryInterface (const IID& riid, void **ppvIF)
   {
       if (IID_IGlastDetSvc == riid) {
           *ppvIF = dynamic_cast<IGlastDetSvc*> (this);
           return StatusCode::SUCCESS;
       }
       else {
           return Service::queryInterface (riid, ppvIF);
       }
   }

   Note: Implement the methods that you defined in your Interface class(es) for this particular service.

3. Make your service available to be dynamically loaded at run time. This is accomplished within your package's packagename_load() and packagename_dll() routines.

Currently, the convention is to place these files within a directory called Dll under the package's src directory.

Example for a service, called GlastDetSvc: 
(Taken from GlastSvc/GlastSvc_load.cpp):

#include "GaudiKernel/DeclareFactoryEntries.h"

DECLARE_FACTORY_ENTRIES(GlastSvc) {
    DECLARE_SERVICE( GlastDetSvc);
}

There is also a GlastSvc_Dll.cpp file defined as follows:

#include "GaudiKernel/LoadFactoryEntries.h"
LOAD_FACTORY_ENTRIES(GlastSvc)

2. Ensure that the shared library containing this service is loaded by updating any jobOptions files for jobs where you want this service available.

Also See:

• Gaudi Developer Guide, Section 11.11 Developing new services.

Owned by: Heather Kelly