// created by crodas -- Public domain

// private, number of running processes
var running = 0;

// sort of try time
exports.time  = 10;
// limit, max 5 running processes
exports.limit = 5;

exports.exec = function(callback) {
    if (typeof callback != "function") {
        throw ("callback is not a valid function");
    }
    var i = setInterval(function() {
        if (running < exports.limit) {
            running++;
            callback();
            running--;
            clearInterval(i);
        }
    }, exports.time);
};