SKILL - determine when asynchronous task complete

I am new to SKILL, so this may be an easy question for someone to answer:

I am working on a custom SKILL interface that is made up of a Tree Table.  In order to generate the report, I have to expand all of the items in the tree.  When I expand the tree items, there is a callback that generates an asynchronous method to get information from a command line script that updates information in the tree, and then updates the GUI with the information through another callback.  This asynchronous update is performed for each item in the tree.  For large trees, this expanding and updating could take 10-20 minutes.

In order to generate my report, I need to expand all of the items in the tree, and then wait for the asynchronous update to complete before I can generate my report to export.

I see that I have 3 options:

1.  Figure out a way to execute a callback function when all of the updates are done (is this possible?)
2.  for the report output, implement a synchronous update as each item is expanded, and wait for each item to be updated, and when the last update is updated generate the report
3.  Poll the asynchronous process, or the data, with an hiSleep() , until the last process is complete, all the fields for each Tree item is populated, or a global variable that would track each item's status, and then run the report

I have implemented #3, and it works, but it does not seem to be the most appropriate solution, so I am looking for suggestions.

Thanks,

- Nellis