[Relfs-devel] A first attempt for plugins

[Vincenzo a. N. N. <vin...@ya...>]

When the cvs commit I just made will be available, there will be a file 
named "PLUGIN_HOWTO.txt" in the top directory. There is an 
implementation for plugins, with a base class called "Index", defined 
in "IndexPlugin.h". Each operation of this class takes a "File" as an 
argument. "File" represents a cache of information we already know 
about files. Things will change a lot.

By now I would like to focus on the plugin interface. Once that is 
settled, an asynchronous proxy for plugins, a dlopen interface and all 
the rest can be written (since I realize that by now these are just 
source-code plugins, and cannot be really "plugged in"). I would like 
opinions on the interface.

The protected method "getParent" has a "watch_OPERATION" for each 
operation, which takes an "Index" as an argument. This allows for a 
plugin to add other plugins to the indexing chain (e.g. when it's a 
proxy).

The protected method "getConnection" is given. It can be overloaded, 
this has been made so that an "asynchronous proxy plugin" can be 
implemented, which does not allow to directly access the main db 
connection (libpqxx does not allow concurrent access to a connection), 
but creates a new connection in the overloaded "getConnection" method.

By the use of preprocessor macros (ARGH!) code size is greatly reduced, 
at the expense of readability if one does not read the "FOR_ALL" macros 
like the one at the top of "IndexPlugin.h".

The next step is to implement some useful plugin (those already present 
are implemented quick & dirty, and do not work properly, they must be 
regarded as examples).

Bye

Vincenzo