PriorityBlockingQueue

PriorityBlockingQueue is a concurrent, blocking queue that orders elements based on their natural ordering or by a specified Comparator. It is part of the Java Concurrency Utilities package. Elements are retrieved from the queue in the order determined by their priority. The head of the queue is the least eligible element with respect to the specified ordering.

Unlike a regular PriorityQueue, PriorityBlockingQueue is thread-safe and designed for use in multi-threaded environments. When a thread attempts to retrieve an element from an empty PriorityBlockingQueue, it will block until an element becomes available. Similarly, if the queue has a fixed capacity and is full, threads attempting to insert elements will block until space becomes available.

The operations available on PriorityBlockingQueue include adding elements (offer, put), retrieving elements (poll, take), and inspecting the head element (peek). The put operation will block indefinitely if the queue is full, whereas offer will return false. The take operation will block indefinitely if the queue is empty, whereas poll will return null.

PriorityBlockingQueue does not accept null elements. If null elements are inserted, a NullPointerException will be thrown. The ordering of elements is crucial for its functionality, and elements must implement the Comparable interface or a Comparator must be provided during instantiation. This ensures that the queue can correctly determine the priority of each element.