Question

I have been programming with Node.js for a little while, and I have found myself becoming increasingly annoyed with the need to chain callbacks. For example, when you need multiple models from a database as shown:

Person.findOne({ 'name.last': 'Ghost' }, 'name occupation', function (err, person) {
    Schedule.findOne({'person_id': person.id }, 'events', function(err, schedule) {
        ...
    }
})

I am looking for solutions to this problem. One idea I had was to do something like this:

function() {
    var p;
    var s;
    var done = false;

    Person.findOne(..., ..., function(err, person) {
        p = person;
        done = true;
    });

    while(!done){}
    done = false;

    Schedule.findOne(..., ..., function(err, schedule) {
        s = schedule;
        done = true;
    });

    while(!done){}
    done = false;

    // ...
}

If I do my queries like this, what are the performance implications? I’m also open to other ideas for solving this problem.

Answer 1

To answer your most direct question, the performance implication of spin-waiting for a callback is that the spin-wait may starve other, more useful tasks from being completed, either in the same process or on the same machine. If your application were running on a single-user machine with no power management, this wouldn’t matter, but neither of those things is likely. Busy-waiting will destroy battery life on mobile platforms, increase electricity costs in the datacenter, and make future maintainers of the code curse your name!

As elclanrs already suggested in a comment, you could look at the “async” library to help streamline your code, but in any case you should avoid busy waiting.