promisekeeper

An industrial grade native promise scheduling library. Automatically limit number of promises running in parallel.

Because unmanaged promises at scale are a disaster you don't even consider until you face it.

A case in point

Promise.all(userList.map(user => {
  return sendPolicyUpgradeMail(user);
})).then(() => {
  res.send("All Done");
});

There is nothing wrong with the above code. Nothing until your userList is at the scale of 10,000,000. Imagine all the calls to sendPolicyUpgradeMail occuring simultaneously. Your RAM is going to be overflowed pretty soon, especially if you're doing any kind of template rendering inside that method. Same is true for database calls and most i/o.

Of course, ideally you would have these implemented in another microservice but even then, your promises will take up memory at the very least linearly to your list. That's where PromiseKeeper comes into play. It manages your promises automatically. Instead of the above code, you write -

PromiseKeeper.mapList(10000, userList, (user) => {
  return sendPolicyUpgradeMail(user);
}).then(() => {
  res.send("All Done");
});

Above call to PromiseKeeper.mapList will ensure that there's at most 10000 (or any number you specify). As soon as a promise is resolved, a new one will take it's place. Once all the promises are resolved, PromiseKeeper.mapList behaves exactly the same way as Promise.all (as in, it returns a promise).

How about async functions?

Async functions work just fine as well.

const myfunc = async () => {
  await PromiseKeeper.mapList(10000, userList, async (user) => {
    await sendPolicyUpgradeMail(user);
  });
}

How to use?

Install with npm i @ishafayet/promisekeeper.

Require with const PromiseKeeper = require('@ishafayet/promisekeeper');

What if I'm not using Array.map?

There is a lower level class PromiseKeeper.PromiseKeeper. It can be used to manage other kind of bulk promises. Documentation on that is coming soon.

LICENSE

MIT