Monday, January 25, 2010

Libraries becoming plugins, plugins becoming libraries

Let me post about some of the latest changes on the CLAM build system.

The CLAM project has been distributing two kinds of shared libraries: the main library modules (core, audioio and processing) and a set of plugins which are optional (spacialization, osc, guitareffects...). Plugins are very convenient since programs like the NetworkEditor can be extended without recompile and enable third party extensions. They are so convenient that we were seriously considering splitting processing and auidioio as plugins.

But the use of content of a clam plugin is limited to abstract Processing interface. No other symbols are visible from other components. That has a serious impact on the flexibility to define plugin boundaries. For example, if a plugin defines a new data token type, any processings managing that token type should be in that same plugin. To use symbols of one plugin from another implies installing headers, provide soname, linker name and so on. That is, building a module library.

So, if plugins want to be libraries and libraries want to be plugins, let them all be both. Each module will be compiled as library (, with soname (, linker link (, headers (include/CLAM/mymodule/*), pc file... and it will also provide a plugin library ( which has no symbol by itself but is linked against the module library. When a program loads such a plugin, all the processings in the module library become available via the abstract interface. On the other side, if program or a module needs to use explicitly the symbols of another module, it just has to include the headers and link against the module library.

I just applied the changes to the plugins and seems to work nicely. Adapting the main modules will be harder because the old sconstruct file, but it is a matter of days and we can split them. I moved a lot of common SCons code to the scons tool. There is a cute environment method called ClamModule which generates a clam module including the module library, soname, linker name, plugin, pkg-config, and install targets. I also added some build system freebies for the modules and applications:

  • All the intermediate generated code apart in a 'generated' directory
  • Non verbose command line
  • Colour command line
  • Enhanced scanning methods with black lists

Well, do not rely too much on the current clam scons tool API. Changes are still flowing through the subversion. Of course, warn me if I broke something. ;-)

No comments: