Potentially merging cxx-mem-model with mainline.

Benjamin Kosnik bkoz@redhat.com
Thu Oct 27 05:22:00 GMT 2011

> Whats left
> ===========
> Functionality is pretty much complete, but there are a few minor lose 
> ends still to deal with. They could be done after a merge, in the
> next stage, or required before... you tell me :-)
> - potentially implement -f[no]-inline-atomics  (to never produce
> inline code and always call the library) and
> -f[no]-atomic-compare-swap-loop (To not fall back to a
> compare_and_swap loop to implement missing functionality)
> - unaligned objects have undefined behaviour at the moment.
> Behaviour could be defined and add alignment checks and a parameter
> to __atomic_is_lock_free() for alignment checking purposes.  Anything
> which doesn't map to one of the properly aligned  5 sized built-ins
> gets a library call.

> - A bit of C++ template restructuring in the include files to remove
> the old fall back locked implementation and fully use the new
> __atomic builtins. (*in progress now*)

Hit me off-line about this. Hopefully I can help expedite.
> - Change external library calls for __atomic_op_fetch routines.
> (*patch submitted already*)
> - There are a bunch of new tests that have been developed along the
> way, but I I expect to spend the next 2 months writing more detailed
> and specific runtime and compile time tests. And of course, fixing
> any of the fall out from those tests.

Yes. I don't see this as a blocker for the merge.

> The final word
> =============
> So what is the opinion/consensus on merging the branch?  It would be 
> nice to get this infrastructure in place for this release so we can
> get people to start using it, and then we can work out any issues
> that arise.
> I'd have Aldy do the actual merge because if I do something will go
> amok for sure.  I wont be around this weekend to fix any fallout, but
> I am around until Friday evening.  I'm around all next week.  I don't 
> anticipate much problem since this is all new functionality for the
> most part, and mainline was merged with the branch a week or two ago.

I am really expecting this branch to be merged for 4.7. The current
status is very presentable IMHO.


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