Locking with redlock bunch of user IDs

locking.js

/**
 * Creates a promise that resolves to either null when no lock was acquired or to user ID if lock was successful
 * @param userId
 * @returns {Function} async function (promise)
 */
const getLockPromise = (userId) => {
	const lockKey = `send-notifications-lock:${userId}`;

	return async () => {
		try {
			await redlock.acquireLock(lockKey, { retry: 0 });

			return userId;
		} catch (e) {
			if (e instanceof CantLockRecordError) {
				logger.debug(`Could not acquire lock for user ${userId}`);
			} else {
				logger.error(e);
			}

			return null;
		}
	};
};

/**
 * Returns only the user IDs that the lock was acquired for
 * @param userIds array
 * @returns User IDs that were locked
 */
const lockUsersForNotifications = async (userIds) => {
  const lockedUserIds = (await Promise.all(userIds.map(userId => getLockPromise(userId))))
    .filter(userId => userId !== null);
                         
  return lockedUserIds;
};