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stdexec::when_all: P3887 #1666

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Merged
merged 1 commit into from
Oct 26, 2025
Merged

stdexec::when_all: P3887 #1666

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29 changes: 15 additions & 14 deletions include/stdexec/__detail/__when_all.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -137,13 +137,12 @@ namespace stdexec {
using __f = __meval<
__concat_completion_signatures,
__meval<__eptr_completion_if_t, __all_nothrow_decay_copyable_results<_Senders...>>,
completion_signatures<set_stopped_t()>,
__minvoke<__with_default<__qq<__set_values_sig_t>, completion_signatures<>>, _Senders...>,
__transform_completion_signatures<
__completion_signatures_of_t<_Senders, _Env...>,
__mconst<completion_signatures<>>::__f,
__set_error_t,
completion_signatures<>,
completion_signatures<set_stopped_t()>,
__concat_completion_signatures
>...
>;
Expand Down Expand Up @@ -191,7 +190,7 @@ namespace stdexec {

struct _INVALID_ARGUMENTS_TO_WHEN_ALL_ { };

template <class _ErrorsVariant, class _ValuesTuple, class _StopToken>
template <class _ErrorsVariant, class _ValuesTuple, class _StopToken, bool _SendsStopped>
struct __when_all_state {
using __stop_callback_t = stop_callback_for_t<_StopToken, __on_stop_request>;

Expand Down Expand Up @@ -222,7 +221,11 @@ namespace stdexec {
}
break;
case __stopped:
stdexec::set_stopped(static_cast<_Receiver&&>(__rcvr));
if constexpr (_SendsStopped) {
stdexec::set_stopped(static_cast<_Receiver&&>(__rcvr));
} else {
STDEXEC_UNREACHABLE();
}
break;
default:;
}
Expand All @@ -243,7 +246,11 @@ namespace stdexec {
using _Traits = __traits<_Env, _Child...>;
using _ErrorsVariant = _Traits::__errors_variant;
using _ValuesTuple = _Traits::__values_tuple;
using _State = __when_all_state<_ErrorsVariant, _ValuesTuple, stop_token_of_t<_Env>>;
using _State = __when_all_state<
_ErrorsVariant,
_ValuesTuple,
stop_token_of_t<_Env>,
(sends_stopped<_Child, _Env> || ...)>;
return _State{sizeof...(_Child)};
};
}
Expand Down Expand Up @@ -309,15 +316,9 @@ namespace stdexec {
// register stop callback:
__state.__on_stop_.emplace(
get_stop_token(stdexec::get_env(__rcvr)), __on_stop_request{__state.__stop_source_});
if (__state.__stop_source_.stop_requested()) {
// Stop has already been requested. Don't bother starting
// the child operations.
stdexec::set_stopped(static_cast<_Receiver&&>(__rcvr));
} else {
(stdexec::start(__child_ops), ...);
if constexpr (sizeof...(__child_ops) == 0) {
__state.__complete(__rcvr);
}
(stdexec::start(__child_ops), ...);
if constexpr (sizeof...(__child_ops) == 0) {
__state.__complete(__rcvr);
}
};

Expand Down
4 changes: 2 additions & 2 deletions test/exec/test_fork.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,7 @@ namespace {
STATIC_REQUIRE(
set_equivalent<
completion_signatures_of_t<decltype(sndr), env<>>,
completion_signatures<set_value_t(), set_error_t(std::exception_ptr), set_stopped_t()>
completion_signatures<set_value_t(), set_error_t(std::exception_ptr)>
>);
}

Expand Down Expand Up @@ -65,7 +65,7 @@ namespace {
STATIC_REQUIRE(
set_equivalent<
completion_signatures_of_t<decltype(sndr), env<>>,
completion_signatures<set_value_t(int, int), set_error_t(std::exception_ptr), set_stopped_t()>
completion_signatures<set_value_t(int, int), set_error_t(std::exception_ptr)>
>);

auto [i1, i2] = sync_wait(sndr).value();
Expand Down
25 changes: 21 additions & 4 deletions test/stdexec/algos/adaptors/test_when_all.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -232,12 +232,14 @@ namespace {
ex::when_all(ex::just(13), ex::just_error(std::exception_ptr{}), ex::just_stopped()));
}

TEST_CASE("when_all has the sends_stopped == true", "[adaptors][when_all]") {
check_sends_stopped<true>(ex::when_all(ex::just(13)));
check_sends_stopped<true>(ex::when_all(ex::just_error(-1)));
TEST_CASE(
"when_all has sends_stopped == true if and only if at least one child sends stopped",
"[adaptors][when_all]") {
check_sends_stopped<false>(ex::when_all(ex::just(13)));
check_sends_stopped<false>(ex::when_all(ex::just_error(-1)));
check_sends_stopped<true>(ex::when_all(ex::just_stopped()));

check_sends_stopped<true>(ex::when_all(ex::just(3), ex::just(0.14)));
check_sends_stopped<false>(ex::when_all(ex::just(3), ex::just(0.14)));
check_sends_stopped<true>(ex::when_all(ex::just(3), ex::just_error(-1), ex::just_stopped()));
}

Expand Down Expand Up @@ -381,4 +383,19 @@ namespace {
wait_for_value(std::move(snd), std::string{"hello world"});
}
}

TEST_CASE("when_all defers stop handling to its children", "[adaptors][when_all]") {
ex::inplace_stop_source source;
source.request_stop();
auto snd = ex::when_all(ex::just(), ex::just());
static_assert(set_equivalent<
ex::completion_signatures_of_t<decltype(snd), ex::env<>>,
ex::completion_signatures<ex::set_value_t()>>);
auto env = ex::prop(ex::get_stop_token, source.get_token());
static_assert(set_equivalent<
ex::completion_signatures_of_t<decltype(snd), decltype(env)>,
ex::completion_signatures<ex::set_value_t()>>);
auto op = ex::connect(snd, expect_void_receiver{});
ex::start(op);
}
} // namespace
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