FIFOrotation

FIFOrotation is a queued processing policy that combines the First-In, First-Out (FIFO) principle with periodic rotation of items within the queue. It is designed to preserve a predictable order while mitigating issues that can arise when service times vary or when long queues lead to unfair wait times.

In a FIFOrotation system, items are enqueued in arrival order. At regular intervals, or after a specified number of operations, the queue undergoes a rotation that reorders positions according to a fixed offset. The rotation is implemented as a logical circular shift, so the next item to be served is determined by the current offset, while the relative ordering of items behind the offset remains FIFO within their rotated segment.

Variants include full rotation, where every item is shifted by a fixed count; partial rotation, which rotates only a portion of the queue; and adaptive rotation, where the offset adapts to measured load or throughput. In software, a rotation counter or a modular index is commonly used to track the offset.

Applications appear in manufacturing, logistics, network packet scheduling, and job queues in operating systems and data processing pipelines, particularly where workload is bursty or where fairness is a concern.

Advantages include reduced risk of starvation, more even resource utilization, and better handling of skewed service rates. Limitations include added complexity, potential deviations from strict FIFO semantics, and the overhead of maintaining rotation state and synchronization in concurrent environments.

See also: FIFO queue, circular buffer, round-robin scheduling, aging, fair queuing.