Let's dive into designing a simplified message queueing system. Imagine you are building a system where different applications need to communicate asynchronously. Instead of directly calling each other, they send messages to a central queue. Consumers then pick up these messages and process them. This decoupling allows for greater flexibility, resilience, and scalability. Our goal is to design the core components of such a system. We'll focus on in-memory implementation and thread safety.

This is a classic problem, but let's make it a bit more realistic. Instead of just strings, let's say our messages are objects that implement a common interface. This allows consumers to handle diverse message types. We also want to support the concept of priority queues, where high-priority messages are processed before low-priority ones. Think of mission-critical alerts jumping to the front of the line. Finally, let's consider the scenarios where multiple producers and consumers interact with the queue concurrently.

Requirements