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declare that stdexec::task is already scheduler-affine #1898

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Merged
ericniebler merged 1 commit into from
Feb 26, 2026
Merged

declare that stdexec::task is already scheduler-affine #1898

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32 changes: 25 additions & 7 deletions include/stdexec/__detail/__task.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -204,6 +204,12 @@ namespace STDEXEC
return __completions_t{};
}

[[nodiscard]]
constexpr auto get_env() const noexcept
{
return __env{};
}

private:
using __on_stopped_t = __task::__on_stopped<stop_source_type>;

Expand All @@ -221,6 +227,16 @@ namespace STDEXEC
static constexpr bool __needs_stop_callback =
__not_same_as<stop_token_type, stop_token_of_t<env_of_t<_Rcvr>>>;

struct __env
{
template <class _Tag>
[[nodiscard]]
constexpr auto query(__get_completion_behavior_t<_Tag>) const noexcept
{
return __completion_behavior::__asynchronous_affine;
}
};

struct __opstate_base
{
constexpr explicit __opstate_base(scheduler_type __sched) noexcept
Expand Down Expand Up @@ -291,7 +307,7 @@ namespace STDEXEC
// If the receiver's stop token is different from the task's stop token, then we need
// to set up a callback to request a stop on the task's stop source when the receiver's
// stop token is triggered:
__stop_callback().__construct(get_stop_token(get_env(__rcvr_)),
__stop_callback().__construct(get_stop_token(STDEXEC::get_env(__rcvr_)),
__on_stopped_t{__var::__get<0>(__coro_.promise().__stop_)});
}
__coro_.resume();
Expand All @@ -304,7 +320,7 @@ namespace STDEXEC
{
if constexpr (__std::constructible_from<__own_env_t, env_of_t<_Rcvr>>)
{
return __own_env_t(get_env(__rcvr));
return __own_env_t(STDEXEC::get_env(__rcvr));
}
else
{
Expand All @@ -320,7 +336,7 @@ namespace STDEXEC
}
else if constexpr (__std::constructible_from<_Env, env_of_t<_Rcvr>>)
{
return _Env(get_env(__rcvr));
return _Env(STDEXEC::get_env(__rcvr));
}
else
{
Expand All @@ -330,9 +346,9 @@ namespace STDEXEC

static auto __mk_sched(_Rcvr const & __rcvr) noexcept -> scheduler_type
{
if constexpr (requires { scheduler_type(get_scheduler(get_env(__rcvr))); })
if constexpr (requires { scheduler_type(get_scheduler(STDEXEC::get_env(__rcvr))); })
{
return scheduler_type(get_scheduler(get_env(__rcvr)));
return scheduler_type(get_scheduler(STDEXEC::get_env(__rcvr)));
}
else
{
Expand Down Expand Up @@ -398,11 +414,12 @@ namespace STDEXEC
STDEXEC::set_stopped(static_cast<_Rcvr&&>(__rcvr_));
}

[[nodiscard]]
auto __get_allocator() noexcept -> allocator_type final
{
if constexpr (requires { allocator_type(get_allocator(get_env(__rcvr_))); })
if constexpr (requires { allocator_type(get_allocator(STDEXEC::get_env(__rcvr_))); })
{
return allocator_type(get_allocator(get_env(__rcvr_)));
return allocator_type(get_allocator(STDEXEC::get_env(__rcvr_)));
}
else
{
Expand Down Expand Up @@ -457,6 +474,7 @@ namespace STDEXEC
}
}

[[nodiscard]]
auto unhandled_stopped() noexcept -> __std::coroutine_handle<>
{
__state_->__canceled();
Expand Down