47Implement promisePool() using worker loops

Implement promisePool(tasks, concurrency, { settle = false } = {}). tasks is an array of functions that each return a promise. The pool runs at most concurrency of them at a time and resolves with their results in input order.

Use the worker loop pattern: start concurrency async loops that each keep taking the next task until none are left.

• With settle: false (default), reject on the first failure and start no new tasks.
• With settle: true, never reject; resolve with { status: "fulfilled", value } or { status: "rejected", reason } per task, like Promise.allSettled.

const tasks = files.map((file) => () => upload(file)); // not started yet
const urls = await promisePool(tasks, 3);

Requirements

• A task function is only called when a worker is free to run it.
• At most concurrency tasks run at once.
• Results keep the input order.
• concurrency below 1 is treated as 1.