petri-net

Is there a tool to model/simulate software concurrency?

Is there a good tool out there that can model an application concurrency/locking scheme in a graphical way and that can simulate some of the aspects? I know that Petri nets can be used for that more or less, but I don't know a good GUI tool that can design and simulate. Is UML in any way usable for such purposes? Any good links are ...

How does rule-based verification with Petri nets work and what is this good for?

A friend just pointed me out to an new development in computer science called "rule based verification with Petri nets". He's not a computer guy but an artist, so I wonder if that's really something cool I must look at? Over the phone he told me from reading and translating an newspaper in Russian, that this fancy new technology is all a...