Java Development Tools

In my ADF application I have a page for creating reports. When I hit create report button, I call window.open() to open report page in other window. This new opened window after onload action fires generateReport backing bean. After report is created, bean is outputing it via FacesContext -> getExternalContext() -> getResponse() -> getOutputStream() -> write(MyReport).

The problem is that if the requested report is big, it takes time (few minutes) to create it.
I need to make my main window operational, but when I try to open a link on my main page, my request is not performed until report in other page is finished. I get
[1050] WARNING: The thread, HTTPThreadGroup-4, is waiting for a oracle.jbo.common.Lock
I thougth, I get the lock just when I try to access database, but this lock doesnt allow accessing static pages on server until the report is finished.
Can someone expalin the problem? Or solution to this:)