lib/async/index.js
function Notifier () {

  // Create the serial execution context mechanism.
  this.csFactory = createLockFactory();

  // The private files collection
  // Contains a file and timer: "filename": {timer: timerid}
  // Used for tracking work left to do. When empty, work is done.
  this.files = {};

  // Contains files successfully processed
  this.filesDone = [];

  // Contains files unsuccessfully processed
  this.filesNotDone = [];

  // true if a timeout occurred, or set by abort
  this.errors = [];

  // the holder of the current failure timeout padding
  this.padTimeout = TIMEOUT_PAD_FLOOR;

  // our reference to the listener
  this.callback = null;

  // our reference to the watcher (an interval id)
  // initial value undefined is important
  // this.watcher;

  // the working pollInterval for this run
  // this.interval

  // flag set by qEmpty callback
  // when the last item from the queue is given to a worker
  this.qempty = false;
}
function Notifier () {

  // Create the serial execution context mechanism.
  this.csFactory = createLockFactory();

  // The private files collection
  // Contains a file and timer: "filename": {timer: timerid}
  // Used for tracking work left to do. When empty, work is done.
  this.files = {};

  // Contains files successfully processed
  this.filesDone = [];

  // Contains files unsuccessfully processed
  this.filesNotDone = [];

  // true if a timeout occurred, or set by abort
  this.errors = [];

  // the holder of the current failure timeout padding
  this.padTimeout = TIMEOUT_PAD_FLOOR;

  // our reference to the listener
  this.callback = null;

  // our reference to the watcher (an interval id)
  // initial value undefined is important
  // this.watcher;

  // the working pollInterval for this run
  // this.interval

  // flag set by qEmpty callback
  // when the last item from the queue is given to a worker
  this.qempty = false;
}
Notifier Constructor
Polls the outputDir and when all the files exist,
calls the listener indicating the snapshots are done.