The barrier can be used to control concurrent flows in NodeJS. It counts how often the function returned is called and executes the callback if it has been called "count" times.

Barrier flow control for NodeJS

/* 
 * A barrier that counts how often a function is called.
 */

module.exports = function(count, callback) {
    var c = count;

    // if count is 0 execute callback
    if(c == 0)
        callback();

    // callback will be executed after this function was called count times
    return function() {
        c--;

        if(c == 0)
            callback();

        return c;
    };
};

Example

var barrier = require("barrier"),
    items = [1, 2, 3],
    next = barrier(items.length, function() {
        console.log("finished");
    });

items.forEach(function(i) {
    // do something async with i here
    setTimeout(next, 1000);
});

https://github.com/berb/node-barrierpoints ;-)

Yeah everyone has his barrier ;)
But I like the fact to work only with a little function and I also found it very useful that the callback executes immediately if count is zero.