As suggested by pitrou, I wrote an implementation of RLock in C. 
Changes to Python version:
 - no debug message: i leave the message in #if 0 ... #endif
 - acquire() method argument "blocking" is not a keyword

Notes:
 - RLock has no docstring!
 - In the Python version, RLock._release_save() replaces owner and 
counter attributes before release the lock. But releasing the lock may 
fails and no the object is in an inconsistent state