NAME
mkVFunc - Support for "nested" dynamic loading
SYNOPSIS
mkVFunc xxx.hDESCRIPTION
perl/Tk is designed so that Tk can be dynamically loaded 'on top of' perl. That is the easy bit. What it also does is allow Tk::Xxxx to be dynamically loaded 'on top of' the perl/Tk composite. Thus when you 'require Tk::HList' the shared object .../HList.so needs to be able to call functions defined in perl and functions defined in loadable .../Tk.so . Now functions in 'base executable' are a well known problem, and are solved by DynaLoader. However most of dynamic loading schemes cannot handle one loadable calling another loadable.
Thus what Tk does is build a table of functions that should be callable. This table is auto-generated from the .h file by looking for 'extern' (and EXTERN which is #defined to 'extern'). Thus any function marked as 'extern' is 'referenced' by the table. The address of the table is then stored in a perl variable when Tk is loaded. When HList is loaded it looks in the perl variable (via functions in perl - the 'base executable') to get the address of the table.
The same utility that builds the table also builds a set of #define's. HList.c (and any other .c files which comprise HList) #include these #define's. So that
Tk_SomeFunc(x,y,z)Is actually compiled as
(*TkVptr->V_Tk_SomeFunc)(x,y,z)Where Tk_ptr is pointer to the table.
See:
Tk-b*/pTk/mkVFunc - perl script that produces tables
/tk.h - basis from which table is generated
/tk.m - #define's to include in sub-extension
/tk_f.h - #included both sides.
/tk_f.c - Actual table definition.
/tk.t - 'shared' set of macros which produce table
included in tk_f.c and tk_f.h
/tkVMacro.h - Wrapper to include *.m filesIn addition to /tk* there are /tkInt*, /Lang* and /tix*