Function _insert

public/javascripts/async.js:860–891

(q, data, pos, callback)

            throw new Error('Concurrency must not be zero');
        }
        function _insert(q, data, pos, callback) {
            if (callback != null && typeof callback !== "function") {
                throw new Error("task callback must be a function");
            }
            q.started = true;
            if (!_isArray(data)) {
                data = [data];
            }
            if(data.length === 0 && q.idle()) {
                // call drain immediately if there are no tasks
                return async.setImmediate(function() {
                    q.drain();
                });
            }
            _arrayEach(data, function(task) {
                var item = {
                    data: task,
                    callback: callback || noop
                };

                if (pos) {
                    q.tasks.unshift(item);
                } else {
                    q.tasks.push(item);
                }

                if (q.tasks.length === q.concurrency) {
                    q.saturated();
                }
            });
            async.setImmediate(q.process);
        }
        function _next(q, tasks) {
            return function(){
                workers -= 1;