What is producer consumer design pattern? Code example, prefarably in C++ would be helpfull. I couldn't find it in gang of four book nor via quick google search.
You are looking at something which uses a combination of two known design patterns, not a single design pattern "visiting producer-consumer".
Your documentation (judging from your description in comments) seems quite clear on this.
Design patterns are meant to be used in combination, their definition is usually flexible (i.e. no code specified).
You can probably read up on both mentioned patterns and identify the code parts which implement them.