Apache Flink - How to destroy global window and release it's resources

[M Singh]

Hi:
I have a use case where I need to create a global window where I need to wait 
for unknown time for certain events for a particular key.  I understand that I 
can create a global window and use a custom trigger to initiate the function 
computation.  But I am not sure how to destroy the window after the triggering 
conditions is satisfied and the the events are purged.
If there is any better way of dealing with this situation, please let me know.
Thanks
Mans