Thursday, 06 August 2009
The August 2009 mailing for the C++ Standards Committee was published yestoday. This is the post-meeting mailing for the July committee meeting. There isn't a new working draft this time, for one very simple reason: the "Concepts" feature was voted out of C++0x, so huge sections of the draft will have to be changed. Thankfully, the concurrency-related parts had not yet had concepts applied, so will not be affected directly by this.
What does this mean for the timetable? Well, the committee currently intends to issue a new Committee Draft for voting and comments by National Bodies in March 2010. How long it takes to get from that draft to a new Standard will depend on the comments that come back, and the length of the committee's issue lists. This is not intended to be a Final Committee Draft, implying there would be at least one more round of voting and comments. As I understand it, the earliest we could get a new Standard is thus early 2011, though if that were to be the case then the details would be finalised late 2010.
This time, there's only one concurrency-related paper in the mailing:
- N2925: More Collected Issues with Atomics
This paper gathers together the proposed wording for a number of outstanding issues with respect to the atomic data types. This tightens up the wording regards the memory ordering guarantees of fences, and adjusts the overload set for both free functions and member functions to ensure atomics behave sensibly in more circumstances. Crucially, the header for atomic operations is also changed — rather than the <cstdatomic> / <stdatomic.h> pairing from the previous draft there is a single header: <atomic>.
Though futures were discussed, no change was made to the working paper in this regard. Detlef and I have been asked to write a further paper on the topic to incorporate the issues raised at the meeting, which will therefore be in the next committee mailing.
Likewise, the proposals for dealing with the lifetime of
thread_local variables and for launching an asynchronous
task with a return value are still under discussion, and further
papers on those can be expected.
How do you feel about the removal of concepts? Do you think the slip in schedule will have an impact on you? Let me know in the comments.