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Merged
ericniebler merged 3 commits into from
Apr 6, 2026
Merged

add the get_start_scheduler query per P3941R4 #1992

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da768cb
add the `get_start_scheduler` query per P3941R4
ericniebler Apr 5, 2026
579e848
fix bad search/replace
ericniebler Apr 5, 2026
93777e9
avoid portability issue with msvc
ericniebler Apr 5, 2026
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4 changes: 3 additions & 1 deletion .clang-format
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,9 @@ EmptyLineAfterAccessModifier: Never
EmptyLineBeforeAccessModifier: Leave
FixNamespaceComments: true
IfMacros: [
'STDEXEC_CATCH'
'STDEXEC_CATCH',
'STDEXEC_IF_CONSTEVAL',
'STDEXEC_IF_NOT_CONSTEVAL'
]
IncludeBlocks: Preserve
IndentAccessModifiers: false
Expand Down
2 changes: 1 addition & 1 deletion include/exec/async_scope.hpp
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Expand Up @@ -726,7 +726,7 @@ namespace experimental::execution
}

[[nodiscard]]
constexpr auto query(get_scheduler_t) const noexcept -> STDEXEC::inline_scheduler
constexpr auto query(get_start_scheduler_t) const noexcept -> STDEXEC::inline_scheduler
{
return {};
}
Expand Down
14 changes: 6 additions & 8 deletions include/exec/at_coroutine_exit.hpp
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Expand Up @@ -30,10 +30,8 @@ namespace experimental::execution
{
using namespace STDEXEC;

using __any_scheduler_t =
any_receiver_ref<completion_signatures<set_value_t(),
set_error_t(std::exception_ptr),
set_stopped_t()>>::any_sender<>::any_scheduler<>;
using __any_scheduler_t = any_scheduler<any_sender<any_receiver<
completion_signatures<set_value_t(), set_error_t(std::exception_ptr), set_stopped_t()>>>>;

struct __die_on_stop_t
{
Expand Down Expand Up @@ -153,7 +151,7 @@ namespace experimental::execution
auto await_suspend(__std::coroutine_handle<_Promise> __parent) noexcept -> bool
{
// Set the cleanup task's scheduler to the parent coroutine's scheduler.
__coro_.promise().__scheduler_ = get_scheduler(get_env(__parent.promise()));
__coro_.promise().__scheduler_ = get_start_scheduler(get_env(__parent.promise()));
// This causes the parent to be resumed after the cleanup action is performed.
__coro_.promise().set_continuation(__parent.promise().continuation());
// This causes the parent to invoke the cleanup action when it performs the final
Expand Down Expand Up @@ -190,13 +188,13 @@ namespace experimental::execution

struct __env
{
__promise const & __promise_;

[[nodiscard]]
auto query(get_scheduler_t) const noexcept -> __any_scheduler_t
auto query(get_start_scheduler_t) const noexcept -> __any_scheduler_t
{
return __promise_.__scheduler_;
}

__promise const & __promise_;
};

struct __promise : with_awaitable_senders<__promise>
Expand Down
23 changes: 7 additions & 16 deletions include/exec/on_coro_disposition.hpp
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Expand Up @@ -32,10 +32,8 @@ namespace experimental::execution
{
using namespace STDEXEC;

using __any_scheduler =
any_receiver_ref<completion_signatures<set_value_t(),
set_error_t(std::exception_ptr),
set_stopped_t()>>::any_sender<>::any_scheduler<>;
using __any_scheduler = any_scheduler<any_sender<any_receiver<
completion_signatures<set_value_t(), set_error_t(std::exception_ptr), set_stopped_t()>>>>;

template <class _Promise>
concept __promise_with_disposition = __at_coro_exit::__has_continuation<_Promise>
Expand Down Expand Up @@ -99,7 +97,7 @@ namespace experimental::execution
_Promise& __promise = __std::coroutine_handle<_Promise>::from_address(__parent).promise();
return __promise.disposition();
};
__coro_.promise().__scheduler_ = get_scheduler(get_env(__parent.promise()));
__coro_.promise().__scheduler_ = get_start_scheduler(get_env(__parent.promise()));
__coro_.promise().set_continuation(__parent.promise().continuation());
__parent.promise().set_continuation(__coro_);
return false;
Expand Down Expand Up @@ -131,28 +129,21 @@ namespace experimental::execution

struct __env
{
__promise const & __promise_;

[[nodiscard]]
auto query(get_scheduler_t) const noexcept -> __any_scheduler
auto query(get_start_scheduler_t) const noexcept -> __any_scheduler
{
return __promise_.__scheduler_;
}

__promise const & __promise_;
};

struct __promise : with_awaitable_senders<__promise>
{
#if STDEXEC_EDG()
template <class _Action>
__promise(_Action&&, _Ts&&... __ts) noexcept
explicit(STDEXEC_EDG() != 0) __promise(_Action&&, _Ts&... __ts) noexcept
: __args_{__ts...}
{}
#else
template <class _Action>
explicit __promise(_Action&&, _Ts&... __ts) noexcept
: __args_{__ts...}
{}
#endif

auto initial_suspend() noexcept -> __std::suspend_always
{
Expand Down
4 changes: 2 additions & 2 deletions include/exec/reschedule.hpp
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Expand Up @@ -36,7 +36,7 @@ namespace experimental::execution
_WITH_ENVIRONMENT_(_Env)>;

template <class _Env>
using __schedule_sender_t = schedule_result_t<__call_result_t<get_scheduler_t, _Env>>;
using __schedule_sender_t = schedule_result_t<__call_result_t<get_start_scheduler_t, _Env>>;

template <class _Env>
using __try_schedule_sender_t =
Expand All @@ -63,7 +63,7 @@ namespace experimental::execution
auto connect(_Receiver __rcvr) const
-> connect_result_t<__schedule_sender_t<env_of_t<_Receiver>>, _Receiver>
{
auto __sched = get_scheduler(STDEXEC::get_env(__rcvr));
auto __sched = get_start_scheduler(STDEXEC::get_env(__rcvr));
return STDEXEC::connect(STDEXEC::schedule(__sched), static_cast<_Receiver&&>(__rcvr));
}

Expand Down
6 changes: 4 additions & 2 deletions include/exec/static_thread_pool.hpp
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Expand Up @@ -283,7 +283,8 @@ namespace experimental::execution
{
if constexpr (__completes_on<Sender, _static_thread_pool::scheduler, Env>)
{
auto sched = STDEXEC::get_completion_scheduler<set_value_t>(get_env(sndr), env);
auto sched = STDEXEC::get_completion_scheduler<STDEXEC::set_value_t>(get_env(sndr),
env);
static_assert(std::is_same_v<decltype(sched), _static_thread_pool::scheduler>);
return __apply(_transform_bulk{*sched.pool_}, static_cast<Sender&&>(sndr));
}
Expand All @@ -308,7 +309,8 @@ namespace experimental::execution
{
if constexpr (__completes_on<Sender, _static_thread_pool::scheduler, Env>)
{
auto sched = STDEXEC::get_scheduler(env);
auto sched = STDEXEC::get_completion_scheduler<STDEXEC::set_value_t>(get_env(sndr),
env);
return __apply(_transform_iterate{*sched.pool_}, static_cast<Sender&&>(sndr));
}
else
Expand Down
92 changes: 57 additions & 35 deletions include/exec/task.hpp
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Expand Up @@ -45,8 +45,7 @@ namespace experimental::execution
using __any_scheduler_completions =
completion_signatures<set_value_t(), set_error_t(std::exception_ptr), set_stopped_t()>;

using __any_scheduler =
any_receiver_ref<__any_scheduler_completions>::any_sender<>::any_scheduler<>;
using __any_scheduler = any_scheduler<any_sender<any_receiver<__any_scheduler_completions>>>;

static_assert(scheduler<__any_scheduler>);

Expand All @@ -59,17 +58,17 @@ namespace experimental::execution
};

template <class _Ty>
concept __indirect_scheduler_provider = requires(_Ty const & t) {
{ get_env(t) } -> __scheduler_provider;
concept __indirect_start_scheduler_provider = requires(_Ty const & t) {
{ get_start_scheduler(get_env(t)) } -> scheduler;
};

template <class _ParentPromise>
constexpr auto __check_parent_promise_has_scheduler() noexcept -> bool
constexpr auto __parent_promise_has_start_scheduler() noexcept -> bool
{
static_assert(__indirect_scheduler_provider<_ParentPromise>,
static_assert(__indirect_start_scheduler_provider<_ParentPromise>,
"exec::task<T> cannot be co_await-ed in a coroutine that "
"does not have an associated scheduler.");
return __indirect_scheduler_provider<_ParentPromise>;
"does not have an associated start scheduler.");
return __indirect_start_scheduler_provider<_ParentPromise>;
}

template <class _ParentPromise>
Expand All @@ -84,41 +83,59 @@ namespace experimental::execution
__sticky
};

template <__scheduler_affinity _SchedulerAffinity>
struct __optional_scheduler_storage
{
__optional_scheduler_storage() = default;
constexpr explicit __optional_scheduler_storage(__ignore) noexcept {}
};

template <>
struct __optional_scheduler_storage<__scheduler_affinity::__sticky>
{
__optional_scheduler_storage() = default;

template <scheduler _Scheduler>
constexpr explicit __optional_scheduler_storage(_Scheduler __sched) noexcept
: __scheduler_(__sched)
{}

__any_scheduler __scheduler_{STDEXEC::inline_scheduler{}};
};

template <__scheduler_affinity _SchedulerAffinity = __scheduler_affinity::__sticky>
class __default_task_context_impl
class __default_task_context_impl : private __optional_scheduler_storage<_SchedulerAffinity>
{
template <class _ParentPromise>
friend struct __default_awaiter_context;

static constexpr bool __with_scheduler = _SchedulerAffinity == __scheduler_affinity::__sticky;
static constexpr bool __with_affinity = _SchedulerAffinity == __scheduler_affinity::__sticky;

STDEXEC_ATTRIBUTE(no_unique_address)
__if_c<__with_scheduler, __any_scheduler, __ignore> __scheduler_{STDEXEC::inline_scheduler{}};
inplace_stop_token __stop_token_;
inplace_stop_token __stop_token_;

public:
template <class _ParentPromise>
constexpr explicit __default_task_context_impl(_ParentPromise& __parent) noexcept
{
if constexpr (_SchedulerAffinity == __scheduler_affinity::__sticky)
if constexpr (__with_affinity && __parent_promise_has_start_scheduler<_ParentPromise>())
{
if constexpr (__check_parent_promise_has_scheduler<_ParentPromise>())
{
__scheduler_ = get_scheduler(get_env(__parent));
}
// get_start_scheduler is used here to get the parent's "current" scheduler,
// which is the one on which this task has been started (i.e., co_await-ed).
auto __parent_sched = get_start_scheduler(get_env(__parent));
this->__scheduler_ = __parent_sched;
}
}

template <scheduler _Scheduler>
constexpr explicit __default_task_context_impl(_Scheduler&& __scheduler)
: __scheduler_{static_cast<_Scheduler&&>(__scheduler)}
constexpr explicit __default_task_context_impl(_Scheduler&& __sched) noexcept
: __optional_scheduler_storage<_SchedulerAffinity>{static_cast<_Scheduler&&>(__sched)}
{}

[[nodiscard]]
constexpr auto query(get_scheduler_t) const noexcept -> __any_scheduler const &
requires(__with_scheduler)
constexpr auto query(get_start_scheduler_t) const noexcept -> __any_scheduler const &
requires(__with_affinity)
{
return __scheduler_;
return this->__scheduler_;
}

[[nodiscard]]
Expand All @@ -130,7 +147,7 @@ namespace experimental::execution
[[nodiscard]]
constexpr auto query(get_completion_behavior_t<set_value_t>) const noexcept
{
if constexpr (__with_scheduler)
if constexpr (__with_affinity)
{
return completion_behavior::asynchronous_affine | completion_behavior::inline_completion;
}
Expand All @@ -148,24 +165,24 @@ namespace experimental::execution

template <scheduler _Scheduler>
constexpr void set_scheduler(_Scheduler&& __sched)
requires(__with_scheduler)
requires(__with_affinity)
{
__scheduler_ = static_cast<_Scheduler&&>(__sched);
this->__scheduler_ = static_cast<_Scheduler&&>(__sched);
}

template <class _ThisPromise>
using promise_context_t = __default_task_context_impl;

template <class _ThisPromise, class _ParentPromise = void>
requires(!__with_scheduler) || __indirect_scheduler_provider<_ParentPromise>
requires(!__with_affinity) || __indirect_start_scheduler_provider<_ParentPromise>
using awaiter_context_t = __default_awaiter_context<_ParentPromise>;
};

template <class _Ty>
using default_task_context = __default_task_context_impl<__scheduler_affinity::__sticky>;

template <class _Ty>
using __raw_task_context = __default_task_context_impl<__scheduler_affinity::__none>;
using inline_task_context = __default_task_context_impl<__scheduler_affinity::__none>;

// This is the context associated with basic_task's awaiter. By default
// it does nothing.
Expand Down Expand Up @@ -387,7 +404,7 @@ namespace experimental::execution
if (!std::exchange(__p.__rescheduled_, true))
{
// Create a cleanup action that transitions back onto the current scheduler:
auto __sched = get_scheduler(*__p.__context_);
auto __sched = get_start_scheduler(*__p.__context_);
auto __guard = at_coroutine_exit(__compose(unstoppable, STDEXEC::schedule),
std::move(__sched));
// Insert the cleanup action into the head of the continuation chain by
Expand Down Expand Up @@ -483,7 +500,7 @@ namespace experimental::execution

private:
using __scheduler_t =
__call_result_or_t<get_scheduler_t, STDEXEC::inline_scheduler, _Context>;
__call_result_or_t<get_start_scheduler_t, STDEXEC::inline_scheduler, _Context>;

struct __final_awaitable
{
Expand Down Expand Up @@ -541,7 +558,7 @@ namespace experimental::execution

#ifndef __clang_analyzer__
template <sender _CvSender>
requires __scheduler_provider<_Context>
requires __start_scheduler_provider<_Context>
auto await_transform(_CvSender&& __sndr) noexcept -> decltype(auto)
{
if constexpr (__completes_where_it_starts<set_value_t,
Expand All @@ -553,13 +570,13 @@ namespace experimental::execution
else
{
return STDEXEC::as_awaitable(continues_on(static_cast<_CvSender&&>(__sndr),
get_scheduler(*__context_)),
get_start_scheduler(*__context_)),
*this);
}
}

template <class _Scheduler>
requires __scheduler_provider<_Context>
requires __start_scheduler_provider<_Context>
auto await_transform(__reschedule_coroutine_on_t::__wrapper<_Scheduler> __box) noexcept
-> decltype(auto)
{
Expand Down Expand Up @@ -592,6 +609,11 @@ namespace experimental::execution
template <class _ParentPromise>
struct __task_awaiter
{
constexpr __task_awaiter(__std::coroutine_handle<__promise> __coro) noexcept
: __coro_(__coro)
{}
STDEXEC_IMMOVABLE(__task_awaiter);

constexpr ~__task_awaiter()
{
if (__coro_)
Expand Down Expand Up @@ -631,7 +653,7 @@ namespace experimental::execution
return std::move(__var::__get<0>(__coro_.promise().__data_));
}

__std::coroutine_handle<__promise> __coro_;
__std::coroutine_handle<__promise> __coro_{};
__optional<awaiter_context_t<__promise, _ParentPromise>> __context_{};
};

Expand All @@ -640,7 +662,7 @@ namespace experimental::execution
: __coro_(__coro)
{}

__std::coroutine_handle<promise_type> __coro_;
__std::coroutine_handle<promise_type> __coro_{};
};
} // namespace __task

Expand Down
5 changes: 3 additions & 2 deletions include/exec/trampoline_scheduler.hpp
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Expand Up @@ -63,11 +63,12 @@ namespace experimental::execution

struct __attrs
{
template <__one_of<set_value_t, set_stopped_t> _Tag, __queryable_with<get_scheduler_t> _Env>
template <__one_of<set_value_t, set_stopped_t> _Tag,
__queryable_with<get_start_scheduler_t> _Env>
[[nodiscard]]
constexpr auto query(get_completion_scheduler_t<_Tag>, _Env const & __env) const noexcept
{
return get_scheduler(__env);
return get_start_scheduler(__env);
}

template <__one_of<set_value_t, set_stopped_t> _Tag, __queryable_with<get_domain_t> _Env>
Expand Down
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