Message brokers

A message broker is an architectural pattern for enabling application integrations via a message-driven paradigm. You can, for example, make a Python application and integrate it with another that is written in C (or Java). Integrations are vital to an enterprise where different applications are made to cooperate with each other.

Concurrent processing is obviously implied here. As the producers and consumers are completely decoupled (they don't even know if the others exist), the producer and consumer applications could even run on different machines, thereby overlapping the processing and increasing the overall throughput: 

Decoupling is really a central concept when you start thinking about concurrent systems. Designing systems consisting of loosely coupled component systems gives us many benefits. For example, we could reuse the components, which allows us to cut down on development and maintenance costs. It also paves the way for enabling greater concurrency. 

What happens when a consumer produces messages too fast? The messages will be buffered in the broker. This essentially means there is an inherent flow control mechanism at work here. A slow consumer can consume at its own pace. Likewise, the producer can produce messages at its own (faster) pace. As both are oblivious of each other, the overall system works smoothly.