Hello Oliver,
because on the user list a library which allows reuse of threads was requested I've added the defer library, originally developed by Simon Meiklejohn, to the boost vault (concurrent programming - I don't know why it was removed?).
Sometime ago I searched for this lib and -of course- I did not find it :-/ In the meantime I developed my own thread pool library based on boost::threads. It's available at http://threadpool.sourceforge.net and already used by several projects. The framework is extensible and easy-to-use (in case you like boost::function / bind). At the moment I'm working on a task adaptor for combining parallel and sequential tasks e.g. (t1 | t2) & t3. I'm going to take a look at the defer lib soon and would like to discuss about a threadpool solution for boost. Best regards, Philipp