Specifying the initialization function

An initialization function for the class library must be provided to support dynamic loading of the library by the SOM Class Manager. The SOM Class Manager expects that, whenever it loads a class library, the initialization function will create and register class objects for all of the classes contained in the library.

These classes are then managed as a group (called an affinity group). One class in the affinity group has a privileged position-namely, the class that was specifically requested when the library was loaded. If that class (that is, the class that caused loading to occur) is subsequently unregistered, the SOM Class Manager will automatically unregister all of the other classes in the affinity group as well, and will unload the class library. Similarly, if the SOM Class Manager is explicitly asked to unload the class library, it will also automatically unregister and free all of the classes in the affinity group.

It is the responsibility of the class-library creator to supply the initialization function. The interface to the initialization function is given by the following C/C++ prototype:

#ifdef __IBMC__
  #pragma linkage (SOMInitModule, system)
#endif

SOMEXTERN void  SOMLINK SOMInitModule ( long majorVersion,
                                        long minorVersion,
                                        string className);

The parameters provided to this function are the className and the major/minor version numbers of the class that was requested when the library was loaded (that is, the class that caused loading). The initialization function is free to use or to disregard this information; nevertheless, if it fails to create a class object with the required name, the SOM Class Manager considers the load to have failed. As a rule of thumb, however, if the initialization function invokes a <className>NewClass procedure for each class in the class library, this condition will always be met. Consequently, the parameters supplied to the initialization function are not needed in most cases.

Here is a typical class-library initialization function, written in C, for a library with three classes ("A", "B", and "C"):

   #include "a.h"
   #include "b.h"
   #include "c.h"
   #ifdef __IBMC__
     #pragma linkage (SOMInitModule, system)
   #endif

   SOMEXTERN void  SOMLINK SOMInitModule (long majorVersion,
                             long minorVersion, string className)
   {
       SOM_IgnoreWarning (majorVersion);  /* This function makes */
       SOM_IgnoreWarning (minorVersion);  /* no use of the passed */
       SOM_IgnoreWarning (className);     /* arguments.   */
       ANewClass (A_MajorVersion, A_MinorVersion);
       BNewClass (B_MajorVersion, B_MinorVersion);
       CNewClass (C_MajorVersion, C_MinorVersion);
   }

The source code for the initialization function can be added to one of the implementation files for the classes in the library, or you can put it in a separate file and compile it independently.