jQuery.periodic = function (callback, options) {
  callback = callback || (function() { return false; });
  options = jQuery.extend({ },
                          { frequency : 10,
                            allowParallelExecution : false},
                           options);
      var currentlyExecuting = false;
      var timer;
      var controller = {
         stop : function () {
           if (timer) {
             window.clearInterval(timer);
             timer = null;
           }
         },
         currentlyExecuting : false,
         currentlyExecutingAsync : false
      };
      timer = window.setInterval(function() {
         if (options.allowParallelExecution || !(controller.currentlyExecuting || controller.currentlyExecutingAsync))
                 {
            try {
                 controller.currentlyExecuting = true;
                 if (!(callback(controller))) {
                     controller.stop();
                 }
             } finally {
              controller.currentlyExecuting = false;
            }
         }
      }, options.frequency * 1000);
};