Hi all, To keep you informed of the progress on STM: In the middle of August I found a potentially better approach to STM, which uses copies of objects more extensively (something which is neither natural nor easy to do in C/C++, which is probably why it was not researched before). The main change is that all globally visible objects are and stay read-only. A write that occurs in theory on one such object is --- like before --- done inside a local copy of the object. The difference with before is what occurs on commit. Before, the local copy would have its content copied back over the global object. But now, the local copy "becomes" the next version of the global object. It makes the reads simpler and cheaper, because we don't have to worry about other threads committing changes to the object in parallel. We end up with the old version of the global object that says, in its header, "I'm outdated, here's a pointer to some newer version". Obviously, this approach relies on good GC support to eventually collect the old copies. I ended up documenting it extensively there, in a very terse form so far: * https://bitbucket.org/pypy/extradoc/raw/extradoc/talk/stm2012/stmimpl.rst I adapted the high-level testing framework I wrote last year to check that it is, or appears to be, correct (and found of course a couple of subtle bugs): * https://bitbucket.org/arigo/arigo/raw/default/hack/stm/python/c2.py * https://bitbucket.org/arigo/arigo/raw/default/hack/stm/python/test_c2.py And I rewrote and tested it in C: * https://bitbucket.org/arigo/arigo/raw/default/hack/stm/c2 In the next days I will start to adapt PyPy to it. This approach has the advantage over the previous one to not require complex support for the reads, which should also make the JIT backend work more directly. Also, unlike the previous one, this approach works on non-Intel CPUs (the C code has been tested on POWER64). A bientôt, Armin.