Dunno if you’ve seen this paper, but — considering the C++0x memory model work — you might find it interesting: What Do High-Level Memory Models Mean for Transactions?

At the moment, I’m planning to use deferred update (so transactions will have to store local copies of the objects they modify, and overwrite the global versions when committing). Rvalue references in C++0x solve some of the problems with this approach, both speeding it up by turning the second final copy operation into a move, and improving exception safety.

Settling on C++ makes some aspects a lot easier than in, say, Java, but obviously also presents some challenges. Some of the advantages are the high level of type safety enabled by templates, and the built-in mechanism for copying objects. Rather than Java’s Clone() which never really worked well in the first place, and pass-by-reference semantics, C++ passes by value and has a copying mechanism built in at the lowest level with copy constructors, which means taking backup copies of objects is pretty trivial, and can be done on existing types without requiring any intrusive changes (inheriting from some STM base class, for example, or requiring users to implement specific interfaces).

I’ll post some more details soon.