P3552 R2 Add a Coroutine Task Type

[wg21bot]

P3552R0 Add a Coroutine Lazy Type (Dietmar Kühl, Maikel Nadolski)

[gonzalobg]

2025-02-12 SG1 Hagenberg Meeting

SG1 Full Minutes

Forward P3552 to LEWG for C++26 with following improvements

• a better name and that name should be task,
• a customization point replacement for its use of continues_on,
• a proper channel for cancellation,
• support for errors without exceptions,
• support for stop requests into the coroutine scheduler,
• scheduler affinity which should:
  • be the default, and
  • have an opt-out, and
  • allow implementations to not reschedule if they can prove that they already in the right contexts; future features may allow implementations to prove this in more cases; vendors are allowed to do this when they have special knowledge.

SF	F	N	A	SA
7	0	0	1	0

A: like to see a more general concept for scheduler affinity to come to SG1 before we ship something in the standard.

[inbal2l]

2025-02-13 Library Evolution Hagenberg Meeting

P3552R0: Add a Coroutine Lazy Type

2025-02-13 Library Evolution Hagenberg Minutes

Champion: Dietmar Kühl / Maikel Nadolski
Chair: Inbal Levi / Fabio Fracassi
Minute Taker: Eddie Nolan

Summary

POLL: Use the name “std::execution::task” (instead of lazy)

SF	F	N	A	SA
10	13	1	0	0

Attendance: 33 (IP) + 7 (R)
Author's Position: SF
Outcome: Consensus in favor

POLL: Change continue_on into affinity_on (yielding logic for either finishing inline (if possible) or rescheduling to the utility according to scheduler properties)

SF	F	N	A	SA
9	6	2	1	0

Attendance: 33 (IP) + 7 (R)
Author's Position: F
Outcome: Consensus in favor

A: My concern is people might dig their own holes by doing it and being explicit is easier.

POLL: Support for errors without exceptions (pushing it to set_error)

SF	F	N	A	SA
6	6	4	1	1

Attendance: 33 (IP) + 7 (R)
Author's Position: 2xSF
Outcome: Consensus in favor

SA: I think we can make it work in an efficient manner with examining exception_ptr paper that’s in flight, and the promise of optimizing short circuit exceptions.
A: One reason to do that is to run coroutines that don’t have exceptions.

Next Steps

Author got feedback on R0, paper will be seen again by LEWG.

[wg21bot]

P3552R1 Add a Coroutine Task Type (Dietmar Kühl, Maikel Nadolski)