Module queue 

DownloadQueue — a bounded, first-come-first-serve queue over a Downloader (#1435 req. 1): capsule downloads are QUEUED and scheduled a few at a time, not all fired at once.

Why queue at all

The #1423 cache-fill flywheel can enqueue many capsule downloads at once. Launching them all concurrently would saturate this node’s own bandwidth and open unbounded peer connections. The queue caps the number of active downloads (max_active, default 3); the rest wait in arrival order and start as slots free up.

The FCFS guarantee

Submissions run through one FIFO channel drained by exactly max_active worker tasks. A job is received only when a worker is idle, and the channel yields jobs in submission order — so at most max_active downloads run at once and they START in the order they were submitted (no reordering, no starvation).

Each submit returns a QueuedHandle carrying the same live progress event stream and terminal result as a direct Downloader::download, so a caller cannot tell whether its download ran immediately or waited for a slot.

Structs

DownloadQueue

A bounded FCFS scheduler in front of a Downloader: submit as many downloads as you like; at most max_active run concurrently and the rest wait their turn in arrival order.

QueuedHandle

A handle to a queued download: the live progress DownloadEvent stream plus the terminal result via join — the same surface as a direct download, whether it ran now or waited.

Constants

DEFAULT_MAX_ACTIVE_DOWNLOADS

The default number of capsule downloads allowed to run at once (the rest queue).