SG1 in Kona

P0876R6 fiber_context - fibers without scheduler (Oliver Kowalke, Nat Goodspeed)

When a non-empty fiber_context is destroyed...

...we like the previous version of the paper (R5+fixes?).
SF F N A SA
0 4 9 7 1

...we like the paper as proposed (R6).
SF F N A SA
1 0 3 10 9

...we like the paper changed to UB (so the user has to do it all).
SF F N A SA
1 12 6 3 1

...we like the paper changed to invoke a function (in that fiber).
SF F N A SA
6 9 9 0 0 - Increases consensus

The cancellation function should have a default in the TS
SF F N A SA
0 2 4 17 2

After the following changes are applied...

• change ~fiber_context and operator=() to have "requires: is empty" instead of cancelling
• add cancel() and cancel_from_any_thread() that calls the cancellation function if not empty
• replace thread termination when returning an empty fiber_context, with UB
  ...the SG1 design of fiber_context is ready for a TS vehicle
  SF F N A SA
  3 7 0 0 0

We need more SG1 wording review before merging into a TS
SF F N A SA

• Unanimous consent

P0876R8 fiber_context - fibers without scheduler (Oliver Kowalke, Nat Goodspeed)

P0876R9 fiber_context - fibers without scheduler (Oliver Kowalke, Nat Goodspeed)

Based on discussion with JF, this should get language review, and it should start with EWG-I.

EWG-I in Belfast

P0876R9 is ready to bring to EWG as it stands.
SF / F / N / A / SA
2 / 8 / 2 / 1 / 0

(EWG-I did suggest adding a section to the paper to discuss some of the issues that came up, such as TLS and and saving the floating-point state. However, given the poll, I forwarded the paper to EWG without blocking on that revision.)

This was seen by EWG in Belfast, will see again.

P0876R14 was added to LEWG 2023 December electronic poll paper (P30532R0)
(Please note that any design changes should be forwarded via LEWG, preferably, in a separate paper)

I'm told by Hubert that CWG asks for EWG input on the following:

As for the language evolution side, questions include whether a throw; lexically in the "body" of a handler should be allowed to rethrow an exception other than the one that became the currently handled exception when the handler became active. It seems LEWG was of the opinion that std::rethrow_exception(std::current_exception()) in a similar context should be allowed to rethrow such an other exception. The core language design and the library design require synchronization here. I am not aware of EWG having discussed this question. The last reference I found of exceptions in EWG discussion of fibers was a very long time ago. The more general question is whether there should be a per-fiber exception state.

See notes: https://wiki.edg.com/bin/view/Wg21kona2023/CoreWorkingGroup

I agree this is an open question for EWG, although we might hit other corners that need EWG input once the paper has been properly drafted according to the feedback we gave. In other words, feel free to get an EWG response to this particular question at your earliest convenience, but don't be disappointed if the paper comes back to EWG anyway at some later point.

As P0876R14 is currently been polled in Dec 2023 LEWG electronic poll (to be forwarded to LWG), CCing my response from the LEWG mailing list (Dec 24th: https://lists.isocpp.org/lib-ext/2023/12/26286.php).
To summarize from LEWG's perspective: I believe we can move forward with the current LEWG-requested design, and have EWG/Core give their input when possible. If EWG/Core gives contradicting input/brings up issues, LWG can send it back to us.

P0876R14 was forwarded to LWG on LEWG 2023 December electronic poll (P3054R0)

P0876R15 fiber_context - fibers without scheduler (Oliver Kowalke, Nat Goodspeed)

CWG 2024-03-18: Reviewed; needs updates.

CWG 2024-03-21: Reviewed partially.

CWG asks EWG to reconsider the decision to permit implementations with per-thread (as opposed to per-fiber) exception state. Examples of surprise results have been added to the paper. Possible outcomes are to specify a per-fiber exception state, to require implementations to satisfy the existing rules around exceptions without actually requiring separate exception states, or to document the situations with bad outcomes as undefined behavior.

P0876R16 fiber_context - fibers without scheduler (Oliver Kowalke, Nat Goodspeed)