Let's pick up the producer/consumer problem from the last recipe and make it a bit more complicated: We make multiple producers produce items and multiple consumers consume them. In addition to that, we define that the queue shall not exceed a maximum size.
This way not only the consumers have to sleep from time to time if there are no items in the queue, but also the producers have to sleep from time to time when there are enough items in the queue.
We are going to see how to solve this problem with multiple std::condition_variable objects and will also use them in slightly different ways than in the last recipe.
