Implement P3149R11 and P3815R1 #1713

ispeters · 2025-12-14T07:18:48Z

This PR will implement P3149R11 patched with P3815R1.

[exec.scope.concepts]
- concept scope_association
- concept scope_token
[exec.associate]
- associate algorithm
[exec.stop.when]
- stop-when algorithm
[exec.spawn]
- spawn algorithm
[exec.spawn.future]
- spawn_future algorithm
[exec.counting.scopes]
- simple_counting_scope
- counting_scope

copy-pr-bot · 2025-12-14T07:18:51Z

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include/stdexec/__detail/__scope_concepts.hpp

ericniebler · 2025-12-15T16:56:18Z

/ok to test fd9d04b

ispeters · 2025-12-16T17:10:44Z

The latest push includes an implementation of stdexec::associate with some tests, but the tests are incomplete so I haven't marked associate as done in the summary.

I have also tried to address the build failures on the previous iteration, but I don't have a local test environment for the failing build types so I haven't tested the fixes locally, other than to confirm that they still build with my local Clang (i.e. Homebrew clang version 21.1.7).

ispeters · 2025-12-17T04:11:55Z

Rebased on #1717.

ericniebler · 2025-12-22T07:14:10Z

/ok to test f786c00

ericniebler · 2025-12-23T22:24:56Z

/ok to test 97d79ee

ispeters · 2025-12-24T03:35:59Z

I managed to get GCC 12 installed on my Mac and it repro'd the ICE and the build failure in test_stop_when.cpp; I think I've addressed the build failures in GCC, nvcc, and MSVC.

ispeters · 2025-12-24T08:09:46Z

simple_counting_scope still needs more tests, but I did discover that [exec.simple.counting.mem], paragraph 9 has a bug: we need to move the scope to the joined state and return true if count is zero, regardless of the value of state.

ericniebler · 2025-12-24T23:55:35Z

/ok to test cc867f4

ispeters · 2025-12-25T07:37:11Z

I think I've fixed the build breaks in old gcc, nvc++, and MSVC. Getting a repro of the gcc 11 builds was quite a pain—I can't figure out how to get gcc 11 to run properly on macOS Tahoe so I had to use container, which I learned about here. Fixing MSVC is a matter of guessing. I can't run nvc++ on my Mac, but it turns out it's available on Godbolt, and this was very helpful.

I've updated __counting_scopes.hpp rather extensively; I renamed some of the variables in simple_counting_scope to make the naming more consistent, and I've thoroughly documented both the paragraphs in the standard being implemented and my justifications for weaker-than-seq_cst memory orderings.

ispeters · 2025-12-25T20:51:37Z

Pull the guts of simple_counting_scope into a __base_scope and implement both simple_counting_scope and counting_scope in terms of it.

ispeters · 2025-12-25T21:36:34Z

Do some template hoisting and renaming, and replace a single virtual function with a function pointer to cut down on RTTI.

This diff adds a definition for `concept stdexec::scope_association` plus tests confirming it accepts and rejects the expected things.

This diff adds a definition for `concept stdexec::scope_token` plus tests confirming it accepts and rejects the expected things. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

This diff defines `stdexec::associate` and adds some initial tests to confirm it works properly. Still a work in progress.

This diff defines `stdexec::__stop_when` as the implementation of _`stop-when`_ and adds tests to validate the algorithm. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

This diff adds `stdexec::spawn` and its tests. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

This diff adds `stdexec::simple_counting_scope` and `stdexec::counting_scope` plus tests for both. The tests found a spec bug that's been filed as an LWG issue. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

This diff adds `stdexec::spawn_future` and some basic tests. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

This diff probably implements the intended design that stop requests sent to a started future-sender get forwarded to the spawned work. The existing tests still pass, but I don't have new tests to confirm the new behaviour. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

Wrap the call to `std::numeric_limits<std::size_t>::max` in parens so that Microsoft's `max` macro doesn't get in the way.

* Eliminate camel case * Uglify all identifiers * `s/\bassert\b/STDEXEC_ASSERT/g` * Take the address of objects with `std::addressof`

ericniebler · 2026-02-10T19:17:12Z

/ok to test 2775f7c

@ericniebler

Take @ericniebler's suggestion and use `__mapply_q` in `__spawn_future.hpp`.

@ericniebler

Take @ericniebler's suggestion and replace a constrained overload set with a single overload with an internal cascade of constexpr ifs to control the environment selection logic in `__spawn_common.hpp` and to control the stop token construction in `__stop_when.hpp`.

Replace the pure-virtual function in `__spawn_state_base` with a function pointer.

Replace the pure-virtuals in `__try_cancelable` and `__spawn_future_state_base` with function pointers.

@ericniebler

Take @ericniebler's suggestion for a better work-around for what might be a spec bug in howthe base class of `__spawn_future_state` is computed.

Since the stdexec-specific `__variant` type has an uninitialized state, we don't need the `__monostate` variant option to represent "uninitialized". Delete it.

ispeters · 2026-02-10T20:06:54Z

There are still a few things I'd like to improve, but this is probably landable.

ericniebler · 2026-02-10T20:58:15Z

/ok to test 9199dcc

Explicitly specify the template type parameters when constructing a `__fused_token` in `__make_token_fn`.

Uncollide with MSVC's `__nothrow` attribute by renaming `__nothrow` to `__non_throwing`.

ericniebler · 2026-02-10T21:15:42Z

/ok to test 892f971

ericniebler · 2026-02-10T21:56:04Z

/ok to test bdb7f09

ericniebler · 2026-02-10T23:11:25Z

/ok to test 3303429

ispeters force-pushed the p3149_plus_p3815 branch from db2f61a to 9327406 Compare December 15, 2025 00:08

ericniebler reviewed Dec 15, 2025

View reviewed changes

include/stdexec/__detail/__scope_concepts.hpp Show resolved Hide resolved

ispeters force-pushed the p3149_plus_p3815 branch from fd9d04b to 707aed3 Compare December 16, 2025 17:09

ispeters force-pushed the p3149_plus_p3815 branch from 707aed3 to 66f394c Compare December 17, 2025 04:10

ispeters force-pushed the p3149_plus_p3815 branch 2 times, most recently from 96d4661 to f786c00 Compare December 22, 2025 06:42

ispeters force-pushed the p3149_plus_p3815 branch 3 times, most recently from 67262ee to 97d79ee Compare December 23, 2025 21:08

ispeters force-pushed the p3149_plus_p3815 branch from 97d79ee to 95d10a7 Compare December 24, 2025 03:31

ispeters force-pushed the p3149_plus_p3815 branch 2 times, most recently from 52e1755 to 521d849 Compare December 24, 2025 08:06

ispeters force-pushed the p3149_plus_p3815 branch from 521d849 to cc867f4 Compare December 24, 2025 20:05

ispeters force-pushed the p3149_plus_p3815 branch 2 times, most recently from a1dd153 to 9263dab Compare December 25, 2025 07:32

ispeters force-pushed the p3149_plus_p3815 branch from 9263dab to 254887d Compare December 25, 2025 20:51

ispeters force-pushed the p3149_plus_p3815 branch from 254887d to f78a329 Compare December 25, 2025 21:35

ispeters force-pushed the p3149_plus_p3815 branch from f78a329 to e6db1ed Compare December 25, 2025 22:07

ispeters and others added 11 commits February 10, 2026 11:14

Add stdexec::scope_association

8791891

This diff adds a definition for `concept stdexec::scope_association` plus tests confirming it accepts and rejects the expected things.

Add stdexec::scope_token

86e22ef

This diff adds a definition for `concept stdexec::scope_token` plus tests confirming it accepts and rejects the expected things. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

Add stdexec::associate

2c65dac

This diff defines `stdexec::associate` and adds some initial tests to confirm it works properly. Still a work in progress.

Add stdexec::__stop_when

08d1308

This diff defines `stdexec::__stop_when` as the implementation of _`stop-when`_ and adds tests to validate the algorithm. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

Add stdexec::spawn

29c0b28

This diff adds `stdexec::spawn` and its tests. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

Add stdexec::simple_counting_scope and stdexec::counting_scope

401f608

This diff adds `stdexec::simple_counting_scope` and `stdexec::counting_scope` plus tests for both. The tests found a spec bug that's been filed as an LWG issue. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

Add stdexec::spawn_future

a63340d

This diff adds `stdexec::spawn_future` and some basic tests. Co-authored-by: Eric Niebler <eniebler@nvidia.com>

fixes

94c4874

Fix MSVC build

21d29e7

Wrap the call to `std::numeric_limits<std::size_t>::max` in parens so that Microsoft's `max` macro doesn't get in the way.

Conform to coding standard

2775f7c

* Eliminate camel case * Uglify all identifiers * `s/\bassert\b/STDEXEC_ASSERT/g` * Take the address of objects with `std::addressof`

ispeters force-pushed the p3149_plus_p3815 branch from 31ccf35 to 2775f7c Compare February 10, 2026 19:14

ispeters added 5 commits February 10, 2026 11:19

Use __mapply_q

6dbc80a

Take @ericniebler's suggestion and use `__mapply_q` in `__spawn_future.hpp`.

Devirtualize __spawn_state_base

22fd39d

Replace the pure-virtual function in `__spawn_state_base` with a function pointer.

Devirtualize spawn_future

fcb41d0

Replace the pure-virtuals in `__try_cancelable` and `__spawn_future_state_base` with function pointers.

Update the completion signature computation for __spawn_future_state

afd6e39

Take @ericniebler's suggestion for a better work-around for what might be a spec bug in howthe base class of `__spawn_future_state` is computed.

ispeters force-pushed the p3149_plus_p3815 branch from 9bd9635 to afd6e39 Compare February 10, 2026 20:02

Remove __monostate from future's completion variant

9199dcc

Since the stdexec-specific `__variant` type has an uninitialized state, we don't need the `__monostate` variant option to represent "uninitialized". Delete it.

ispeters marked this pull request as ready for review February 10, 2026 20:06

ispeters added 2 commits February 10, 2026 13:13

Fix Clang 16 build

892f971

Explicitly specify the template type parameters when constructing a `__fused_token` in `__make_token_fn`.

Fix MSVC build

bdb7f09

Uncollide with MSVC's `__nothrow` attribute by renaming `__nothrow` to `__non_throwing`.

__callback is magic on msvc

3303429

ericniebler merged commit b62ecdf into NVIDIA:main Feb 10, 2026
22 checks passed

Implement P3149R11 and P3815R1 #1713

Implement P3149R11 and P3815R1 #1713

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