workQueue

A workqueue is a mechanism used in computing to manage and execute tasks asynchronously. It consists of a queue that holds work items and a set of worker threads or a thread pool that processes those items. Submitting work to a queue decouples the task from its execution, allowing the submitting context to continue without waiting for the work to complete. Workqueues are commonly used to handle I/O completion, background processing, or tasks that may block, without blocking the caller.

Key concepts include the work item, the queue or pool that holds items, and the workers that pull items for execution. Work may be scheduled for immediate execution or deferred to a later time. Many implementations support multiple producers and consumers, concurrency control to avoid race conditions, and mechanisms to cancel, flush, or synchronize with in-progress work. Ordering is often FIFO, but some systems offer prioritization or serialized execution for specific work items.

Variants and patterns you might encounter include immediate work, delayed or periodic work (scheduled via timers), and different pool configurations such as fixed-size or dynamically scaled thread pools. Some systems provide per-queue or per-context workgroups to improve locality or ensure specific scheduling guarantees.

Linux kernel workqueues provide a prominent example of this concept in practice. They defer work from interrupt context to process context by running items on kernel threads. The Linux implementation includes system workqueues and per-CPU workqueues, with features for delayed work, cancellation, and flushing. API elements commonly associated with workqueues include queue_work, cancel_work_sync, and creation of specialized queues for particular needs.