Athena Developer Guide

Athena
Chapter 17 Physical design issues Version/Issue: 2.0.0
When a component library is loaded, the framework attempts to locate a single entrypoint, called
getFactoryEntries(). This is expected to declare and load the component factories from the
library. Several macros are available to simplify the declaration and loading of the components via this
mechanism.
Consider a simple package MyComponents, that declares and defines the MyAlgorithm class,
being a subclass of Algorithm, and the MyService class, being a subclass of Service. Thus the
package will contain the header and implementation files for these classes (MyAlgorithm.h,
MyAlgorithm.cxx, MyService.h and MyService.cxx) in addition to whatever other files
are necessary for the correct functioning of these components.
In order to satisfy the requirements of a component library, two additional files must also be present in
the package. One is used to declare the components, the other to load them. Because of the technical
limitations inherent in the use of shared libraries, it is important that these two files remain separate,
and that no attempt is made to combine their contents into a single file.
The names of these files and their contents are described in the following sections.
17.3.1.1 Declaring Components
Components within the component library are declared in a file MyComponents_entries.cxx.
By convention, the name of this file is the package name concatenated with _entries. The contents
of this file are shown in Listing 17.3:
Listing 17.3 The MyComponents_entries.cxx file
#include "Gaudi/Kernel/DeclareFactoryEntries.h"
DECLARE_FACTORY_ENTRIES( MyComponents ) { [1]
DECLARE_ALGORITHM( MyAlgorithm ); [2]
DECLARE_SERVICE ( MyService );
}
Notes:
1. The argument to the DECLARE_FACTORY_ENTRIES statement is the name of the
component library.
2. Each component within the library should be declared using one of the DECLARE_XXX
statements discussed in detail in the next Section.
page 151