DownloadQueues

DownloadQueues is a software subsystem or data structure used to manage and schedule the download of resources. It provides a queueing mechanism to organize tasks, enforce concurrency limits, and coordinate progress tracking and error handling across multiple workers. A DownloadQueue stores entries representing individual downloads, including the resource URL, destination path, and status information such as enqueued, in_progress, completed, failed, or canceled.

Queue behavior may be FIFO or priority-based. A simple implementation processes tasks in arrival order, while more advanced systems assign priority to certain content. Features commonly include concurrency control (maximum parallel downloads), rate limiting, retry policies with exponential backoff, timeout handling, and pause/resume and cancellation support.

Technical components include a queue manager, a worker pool that performs the actual fetch operations, and a persistence layer to survive restarts. Some designs separate the logical queue from the transport layer. Progress is reported through events or callbacks, and completions are recorded in a log or persistent index.

Use cases include download managers, content delivery tools, and software updaters, or any system that downloads resources asynchronously. Considerations encompass fault tolerance, data integrity, network variability, and security issues such as validating certificates and restricting destinations.

See also: task queue, download manager, fetch queue, backoff strategy.