construct/modules

Module Tree

This directory contains dynamically loadable functionality to libircd.

Approach

Unlike most of the module systems found in traditional C free software projects, our approach is oriented around global symbol availability to the address space rather than explicit imports from self-contained modules. This direction is made viable by C++ and advances in the compiler and linker toolchains. The result is significantly simpler and more convenient for developers to work with.

GLOBAL SYMBOLS

Modules are loaded with RTLD_GLOBAL on both posix and windows platforms. Use of C++ namespaces, visibility attributes, STB_GNU_UNIQUE, etc are adequate to make this modernization.

WEAK UNDEFINED SYMBOLS

All project code is built to silently weaken undefined symbols. This means a complicated interface declared in a header, like a class interface with public and private and static members (typical in C++) can be included by itself into any part of the project without knowing where the definitions of that interface are until they are first used at runtime.

If definitions are not available because they are in an unloaded module: a C++ exception is thrown directly from the callsite. We have built this action is built into the lookup mechanism of the runtime dynamic linker; none of this requires knowledge or effort from developers to use.

Layout

(TODO)

Getting started

The header mods/mapi.h is specific to modules and included for modules in addition to the core ircd.h. Both of these are included automatically via the compiler's command-line and the developer does not have to #include either in the module.

1. Every loadable module requires a static ircd::mapi::header with the explicit name of IRCD_MODULE. This is an object which will be sought by the module loader in libircd.

// Example of a trivial module

ircd::mapi::header
IRCD_MODULE
{
	"My Module", []
	{
		puts("hi\n");
	}
};

2. Add an _la_SOURCES entry for your module in the appropriate place in Makefile.am.

3. Add the module .la name to the appropriate LTLIBRARIES list in Makefile.am.