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use start sched/domain as completion sched/domain for senders that are affine #2250

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Merged
ericniebler merged 1 commit into from
Sep 4, 2026
Merged

use start sched/domain as completion sched/domain for senders that are affine #2250

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37 changes: 21 additions & 16 deletions include/stdexec/__detail/__domain.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -243,8 +243,8 @@ namespace STDEXEC
STDEXEC_HOST_DEVICE_DEDUCTION_GUIDE
__hide_query(_Env &&, _Queries...) -> __hide_query<_Env, _Queries...>;

//! @brief A wrapper around an environment that hides the get_start_scheduler and get_domain
//! queries.
//! @brief A wrapper around an environment that hides the get_start_scheduler and
//! get_domain queries.
template <class _Env>
struct __hide_scheduler : __hide_query<_Env, get_start_scheduler_t>
{
Expand Down Expand Up @@ -304,7 +304,8 @@ namespace STDEXEC
static consteval auto __check_domain(_Domain) noexcept -> _Domain
{
// Sanity check: if a completion scheduler can be determined from the attributes
// (not the environment), then its domain must match the domain returned by the attributes.
// (not the environment), then its domain must match the domain returned by the
// attributes.
if constexpr (!__same_as<_Tag, void>)
{
if constexpr (__callable<get_completion_scheduler_t<_Tag>, _Attrs const &, _Env const &...>)
Expand All @@ -330,8 +331,9 @@ namespace STDEXEC
{
using __domain_t = __call_result_t<__read_query_t, _Attrs const &, _Env const &...>;
return __check_domain<_Attrs, _Env...>(__domain_t{});
// Otherwise, if _Tag is void, fall back to querying for the set_value_t completion domain:
}
// Otherwise, if _Tag is void, fall back to querying for the set_value_t completion
// domain:
else if constexpr (__same_as<_Tag, void>)
{
if constexpr (__callable<get_completion_domain_t<set_value_t>,
Expand All @@ -347,8 +349,8 @@ namespace STDEXEC
return void();
}
}
// Otherwise, if __attrs has a completion scheduler, we can ask that scheduler for its
// completion domain.
// Otherwise, if __attrs has a completion scheduler, we can ask that scheduler for
// its completion domain.
else if constexpr (__callable<get_completion_scheduler_t<_Tag>,
_Attrs const &,
_Env const &...>)
Expand All @@ -362,29 +364,32 @@ namespace STDEXEC
using __domain_t = __call_result_t<__read_query_t, __sch_t, _Env const &...>;
return __domain_t{};
}
// Otherwise, if the scheduler's sender indicates that it completes inline, we can ask
// the environment for its domain.
else if constexpr (__completes_inline<_Tag,
env_of_t<__call_result_t<schedule_t, __sch_t>>,
_Env...>
// Otherwise, if the scheduler's sender indicates that it completes where it
// starts, we can ask the environment for its domain.
else if constexpr (__completes_where_it_starts<
_Tag,
env_of_t<__call_result_t<schedule_t, __sch_t>>,
_Env...>
&& __callable<get_domain_t, _Env const &...>)
{
return __call_result_t<get_domain_t, _Env const &...>{};
}
// Otherwise, if we are asking "late" (with an environment), return the default_domain
// Otherwise, if we are asking "late" (with an environment), return the
// default_domain
else if constexpr (sizeof...(_Env) != 0)
{
return default_domain{};
}
}
// Otherwise, if the attributes indicates that the sender completes inline, we can ask
// the environment for its domain.
else if constexpr (__completes_inline<_Tag, _Attrs, _Env...>
// Otherwise, if the attributes indicates that the sender completes where it starts,
// we can ask the environment for its domain.
else if constexpr (__completes_where_it_starts<_Tag, _Attrs, _Env...>
&& __callable<get_domain_t, _Env const &...>)
{
return __call_result_t<get_domain_t, _Env const &...>{};
}
// Otherwise, if we are asking "late" (with an environment), return the default_domain
// Otherwise, if we are asking "late" (with an environment), return the
// default_domain
else if constexpr (sizeof...(_Env) != 0)
{
return default_domain{};
Expand Down
6 changes: 3 additions & 3 deletions include/stdexec/__detail/__schedulers.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -427,7 +427,7 @@ namespace STDEXEC
// Otherwise, if __attrs indicates that its sender completes inline, then we can ask
// the environment for the current scheduler and return that (after checking the
// scheduler for _its_ completion scheduler).
else if constexpr (__completes_inline<_Tag, _Attrs, _Env...>
else if constexpr (__completes_where_it_starts<_Tag, _Attrs, _Env...>
&& (__callable<get_start_scheduler_t, _Env const &> || ...))
{
using __result_t = __call_result_t<__recurse_query_t,
Expand Down Expand Up @@ -461,7 +461,7 @@ namespace STDEXEC
// Otherwise, if __attrs indicates that its sender completes inline, then we can ask
// the environment for the current scheduler and return that (after checking the
// scheduler for _its_ completion scheduler).
else if constexpr (__completes_inline<_Tag, _Attrs, _Env...>
else if constexpr (__completes_where_it_starts<_Tag, _Attrs, _Env...>
&& __callable<get_start_scheduler_t, _Env const &...>)
{
return __check_domain<_Attrs, _Env...>(
Expand Down Expand Up @@ -604,7 +604,7 @@ namespace STDEXEC
template <class _Sch, class _Env>
constexpr auto __mk_sch_env([[maybe_unused]] _Sch __sch, _Env const &__env) noexcept
{
if constexpr (__completes_inline<set_value_t, env_of_t<schedule_result_t<_Sch>>, _Env>
if constexpr (__completes_where_it_starts<set_value_t, env_of_t<schedule_result_t<_Sch>>, _Env>
&& __callable<get_start_scheduler_t, _Env const &>)
{
auto __sch2 = get_completion_scheduler<set_value_t>(get_start_scheduler(__env),
Expand Down
14 changes: 14 additions & 0 deletions test/stdexec/types/test_task.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -654,6 +654,20 @@ namespace
CHECK(!res.has_value());
}

TEST_CASE("test completion domain of task", "[types][task]")
{
// task is scheduler affine but not inline. Regardless, its completion domain is the
// same as the start scheduler's completion domain.
using attrs_t = ex::env_of_t<ex::task<int>>;
using env_t = ex::prop<ex::get_start_scheduler_t, ex::parallel_scheduler>;
using sched_t =
std::invoke_result_t<ex::get_completion_scheduler_t<ex::set_value_t>, attrs_t, env_t>;
using domain_t =
std::invoke_result_t<ex::get_completion_domain_t<ex::set_value_t>, attrs_t, env_t>;
STATIC_REQUIRE(std::same_as<sched_t, ex::parallel_scheduler>);
STATIC_REQUIRE(std::same_as<domain_t, ex::__parallel_scheduler_domain>);
}

TEST_CASE("repro for NVIDIA/stdexec#2041", "[types][task]")
{
auto task = []() -> ex::task<void>
Expand Down
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