I had a working multi-threaded example working a good while ago. The code is lost in the nimbus but I know it's doable. I also ported the Context class a while ago, this should help with context activation. It was never tested so far...
I guess try it, if it doesn't work we'll see what we can do.
![Smiley :)](https://www.sfml-dev.org/forums/Smileys/default/smiley.gif)
By the way, you do not have to do the rendering in an extra thread, you can use a main loop in the main thread without problems. All AWT / Swing events are handled in the separate "AWT Thread" already, so it won't freeze. You just have to deal with AWT events (e.g. button presses) asynchronously. A concurrent list to queue such events to be processed could be of help here.
Also, prepare for more refactoring, I've done a bunch of changes in the master branch to fix remaining design issues. Right now it should all be in its final form. I can't tell when I will merge the RenderCanvas into the master branch. It probably should be in JSFML 1.0, but it has to work properly. I will commence Linux tests some time soon.