Back when we originally added this, the consensus was to leave synchronizition out of the C++ layer and leave this up to whatever framework it is used in.  This is because 

a) on some platforms (such as pre xcode 4, which I think OF still supports, and not to mention VC10), mutex is not in the standard library yet and 
b) C++ is a general use language, whereas thread syncing is domain specific - for instance you don't need it if you are running libpd with just one thread.