Concurrency and timing

Every timer, retry, and queue in these packages takes an AbortSignal. Pass request.signal, and when the client disconnects, the sleeps, retries, and queued tasks that the request started stop instead of running on.

• queue limits how many async tasks run at once, with priorities.
• timers has sleep, retry, poll, debounce, and throttle.
• rate-limit limits requests per key, in memory, Workers KV, a Durable Object, or Redis over HTTP.

Fetch many URLs with a concurrency limit and retries

This function runs at most four requests at once, tries each URL up to three times with backoff, and gives each attempt 10 seconds. Aborting signal stops every request, including the ones still in the queue:

import * as Queue from '@portable/queue';
import * as Timers from '@portable/timers';
 
async function fetchAll(urls: readonly string[], signal: AbortSignal) {
  return Queue.map(
    urls,
    (url, { signal }) =>
      Timers.retry(
        ({ signal }) => fetch(url, { signal }).then((r) => r.text()),
        { attempts: 3, timeout: 10_000, signal },
      ),
    { concurrency: 4, signal },
  );
}