How to check for Threads being Idle?

[jpscarpa]

I am trying to trigger some code, when an application has become idle.
Since it's a Multithreaded application, I would like to wait until all Threads are Idle (or is there a better way to do this)?

Since I do not have the Source Code of the application, I am wondering how I can "hook", to know when I can trigger my code.

I already have found the process Id, and thread id of all relevant threads.

Thanks in advance.

Juan