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stdexec::when_all: Hang After Stop Request #1851

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Merged
ericniebler merged 1 commit into from
Feb 16, 2026
Merged

stdexec::when_all: Hang After Stop Request #1851

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44 changes: 21 additions & 23 deletions include/stdexec/__detail/__when_all.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -285,6 +285,15 @@ namespace STDEXEC {
__on_stop_.reset();
// All child operations have completed and arrived at the barrier.
switch (__state_.load(__std::memory_order_relaxed)) {
case __stopped:
if constexpr (_SendsStopped) {
STDEXEC::set_stopped(static_cast<_Receiver&&>(__rcvr_));
break;
}
// This is reachable because the stop callback sets __stopped whether
// or not any child can send set_stopped, therefore we handle this the
// same as __started
[[fallthrough]];
case __started:
if constexpr (!__std::same_as<_ValuesTuple, __ignore>) {
// All child operations completed successfully:
Expand All @@ -298,13 +307,6 @@ namespace STDEXEC {
__mk_completion_fn(set_error, __rcvr_), static_cast<_ErrorsVariant&&>(__errors_));
}
break;
case __stopped:
if constexpr (_SendsStopped) {
STDEXEC::set_stopped(static_cast<_Receiver&&>(__rcvr_));
} else {
STDEXEC_UNREACHABLE();
}
break;
default:;
}
}
Expand Down Expand Up @@ -489,23 +491,19 @@ namespace STDEXEC {
__state.__stop_source_.request_stop();
}
} else if constexpr (!__same_as<_ValuesTuple, __ignore>) {
// We only need to bother recording the completion values
// if we're not already in the "error" or "stopped" state.
if (__state.__state_.load() == __started) {
auto& __opt_values = STDEXEC::__get<_Index::value>(__state.__values_);
using _Tuple = __decayed_tuple<_Args...>;
static_assert(
__same_as<decltype(*__opt_values), _Tuple&>,
"One of the senders in this when_all() is fibbing about what types it sends");
if constexpr ((__nothrow_decay_copyable<_Args> && ...)) {
auto& __opt_values = STDEXEC::__get<_Index::value>(__state.__values_);
using _Tuple = __decayed_tuple<_Args...>;
static_assert(
__same_as<decltype(*__opt_values), _Tuple&>,
"One of the senders in this when_all() is fibbing about what types it sends");
if constexpr ((__nothrow_decay_copyable<_Args> && ...)) {
__opt_values.emplace(_Tuple{static_cast<_Args&&>(__args)...});
} else {
STDEXEC_TRY {
__opt_values.emplace(_Tuple{static_cast<_Args&&>(__args)...});
} else {
STDEXEC_TRY {
__opt_values.emplace(_Tuple{static_cast<_Args&&>(__args)...});
}
STDEXEC_CATCH_ALL {
__set_error(__state, std::current_exception());
}
}
STDEXEC_CATCH_ALL {
__set_error(__state, std::current_exception());
}
}
}
Expand Down
2 changes: 1 addition & 1 deletion test/stdexec/algos/adaptors/test_when_all.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -404,7 +404,7 @@ namespace {
ex::completion_signatures_of_t<decltype(snd), decltype(env)>,
ex::completion_signatures<ex::set_value_t()>
>);
auto op = ex::connect(snd, expect_void_receiver{});
auto op = ex::connect(snd, expect_void_receiver(env));
ex::start(op);
}

Expand Down