I would like to show progress of multiple Jobs running in parallel, but in only one progress dialog.
But each call to Job.setUser() seems to result in a new progress dialog.
Have you tried using
org.eclipse.ui.progress.UIJob. Checkout this link
http://www.jdg2e.com/ch29.jobs/doc/index.html. https://web.archive.org/web/20090406175007/http://www.jdg2e.com:80/ see the download link at the bottom of the page, though I am not sure how relevant the solution is after 6 years.
The tutorial executes two jobs simultaneously.
The good thing about eclipse is that the source code is readily available :) . Just hack through the progress view source. Essentially the idea is same, what you need to translate is
Progress View -> Composite to
Your Dialog -> Composite.
Hope this will help.