While studying David Butenhof’s classic Programming with POSIX Threads I sketched out the following diagram to help me visualize the example ‘Pipeline’ threading model (for which he provides the source code in Chapter 4).

I have simplified this somewhat (for example, as is standard practice, the predicate is actually checked both before and after the ‘condition wait’ using a while loop), but I believe this helps to convey the basic interactions before digging deeper into the details.