How to reproduce Subtle Memory Leak?

[forgotPassword]

Hello, I can't seem to reproduce the subtle memory leak that should happen when exiting early/incorrectly from the flow. I am running:

// node --inspect-brk --inspect leak.js

var async = require('async');

var run = 0,
    stop = 1000000;

var leak = function(cb){
    var wf = [];

    wf.push(function(next){
        setImmediate(function(){
            // return cb();
            next(null);
        });
    });

    wf.push(function(next){
        setImmediate(function(){
            next(null);
        });
    });

    async.waterfall(wf, function(){
        cb();
    });
};

var loop = function(){
    if(run === stop){
        console.log('done');

        debugger;
        return;
    };

    run++;

    setImmediate(function(){
        leak(loop);
    });
};

loop();

// full : 3.8 MB
// early : 3.8 MB

But in both cases I pretty match get the same heap snapshot. Is this a thing? Can you point to where the code keeps a reference that prevents gc from working? Thanks!

[forgotPassword]

As a sanity check, storing wf[0] in a global variable:

var sanity = [];

...

  sanity.push(wf[0]);

  async.waterfall(wf, function(){
      cb();
  });
...

results in > 100MB of heap.

@aearly, was the leak theoretical or actually encountered in previous node/async versions? Thanks!

[forgotPassword]

If your final callback does only error checking, it seems 2-3% performance boost if you just skip it altogether and return directly.

eg I have a lot of code like this:

...

wf.push(function(results, next){
    res.end(results);
    next(null); // <--- do i really need this?
});

async.waterfall(wf, function(err, result){
    if(err)
        log_err(req, res, err);
});

There can still be use of jump to final cb, eg if your final callback does some cleanup (releasing db connections etc), but next(false) completely stops the whole chain so that is a different issue for now (assuming fake error is the way to go here).

[aearly]

It's likely that JS engines have improved in the years since that line in the docs was written.