buffered-all-settled.ts

buffered-all-settled.ts

const task = (i: number): Promise<number> =>
	new Promise((res, rej) => {
		setTimeout(
			() => {
				if (i % 12 === 0) {
					console.log('task reject', i);
					rej('nope');
				} else {
					console.log('task resolve', i);
					res(i);
				}
			},
			500 + Math.random() * 100,
		);
	});

export const bufferedAllSettled = async <T, E extends Error>(
	tasks: (() => Promise<T>)[],
	bufferSize = 25,
): Promise<PromiseSettledResult<T>[]> => {
	const buffer: Map<() => Promise<T>, Promise<T | E>> = new Map();
	const results: PromiseSettledResult<T>[] = [];
	while (tasks.length) {
		while (buffer.size < bufferSize) {
			const task = tasks.shift()!;
			const promise = task()
				.then((value) => {
					results.push({ status: 'fulfilled', value });
					buffer.delete(task);
					return value;
				})
				.catch((error: E) => {
					results.push({ status: 'rejected', reason: error });
					buffer.delete(task);
					return error;
				});
			buffer.set(task, promise);
		}
		await Promise.any(buffer.values());
	}
	await Promise.allSettled(buffer.values());
	return results;
};

(async () => {
	const tasks = Array.from({ length: 100 }).map((_, i) => () => task(i));
	const results = await bufferedAllSettled(tasks);
	console.log('final results', results);
})();