How can I know that all child thread are gone out?

[Druzhinin Alexandr]

Hello
I spawn several threads and now I need to know if they has finished 
their job. Before I do it by means of messages from child threads to the 
main one to inform about finishing. But I'm sure this isn't good enough, 
because a child thread may fail before sending the exit message to the 
main thread and the application will hang up. So I'd like to check from 
the main thread if child threads are gone away. How can I do it?