Hi Johan,
The way clarion works you can't "open" a file on one thread and have it "open" on all threads. It's possible that if it _is_ open on the main thread then it opens faster on other threads, I'm not sure of that. Personally I wouldn't think that's such a good idea though.
Bear in mind that this is all happening in Ram, and your machine is plenty quick. Opening and closing files is not really that expensive.
Also remember that not all files are opened for every thread. Actually it's a very small number, if any, that are opened.
So, I'm thinking that unless you have some data t the contrary, this just isn't something you need to be worried about.
cheers
Bruce