enqueue

Enqueue is the operation of adding an element to the end of a queue data structure, where the order of elements is typically first in, first out (FIFO). The counterpart is dequeue, which removes and returns the element at the front of the queue.

In data structures, a queue supports enq at the rear and often deq at the front. Implementations include linked lists, which provide O(1) insertion at the tail, and dynamic arrays or circular buffers, which can offer O(1) amortized time but may require resizing or wrap-around logic. Bounded queues have a fixed capacity, while unbounded queues can grow as needed. Correct handling of concurrency is important in multi-threaded contexts to prevent race conditions or data corruption.

In software systems, enqueue is used for scheduling, buffering, and asynchronous processing. In messaging systems, an enqueue operation places a message on a queue for later delivery to a consumer. Enqueued messages may be processed by one or more workers, possibly with delivery guarantees such as at-least-once, exactly-once, or at-most-once, depending on the system. Some queues support prioritization or multiple sub-queues.

Terminology varies: the operation may be called enqueue, enq, offer, or push in different languages or libraries. It is distinct from push, which often refers to stacks in some contexts. Enqueue remains a core concept in algorithms, data structures, and distributed systems for managing ordered, buffered work or messages.