Best programming approach/methodology to assure thread safety

Question

When I was learning Java coming from a background of some 20 years of procedural programming with basic, Pascal, COBOL and C, I thought at the time that the hardest thing about

Answer 1

I suggest the actor model.

Answer 2

1. Avoid sharing data between threads where possible (copy everything).
2. Never have locks on method calls to external objects, where possible.
3. Keep locks for the shortest amount of time possible.

Answer 3

Writing all the code in a multi-threaded application very... carefully! I don't know any better answer than that. (This involves stuff like jonnii mentioned).

I've heard people argue (and agree with them) that the traditional threading model really won't work going into the future, so we're going to have to develop a different set of paradigms / languages to really use these newfangled multi-cores effectively. Languages like Haskell, whose programs are easily parallelizable since any function that has side effects must be explicitly marked that way, and Erlang, which I unfortunately don't know that much about.