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fix(when_any): guard stop callback against inline completion destroying the opstate #2115

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fix(when_any): guard stop callback against inline completion destroying the opstate #2115

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26 changes: 24 additions & 2 deletions include/exec/when_any.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,25 @@ namespace experimental::execution

STDEXEC_IMMOVABLE(__opstate_base);

struct __forward_stop_request
{
constexpr void operator()() const noexcept
{
// Temporarily increment the count to avoid concurrent/recursive arrivals to
// pull the rug under our feet. Relaxed memory order is fine here.
__op_->__count_.fetch_add(1, __std::memory_order_relaxed);

__op_->__stop_source_.request_stop();

// Arrive in order to decrement the count again and complete if needed.
__op_->__arrive();
}

__opstate_base* __op_;
};

using __on_stop =
stop_callback_for_t<stop_token_of_t<env_of_t<_Receiver>&>, __forward_stop_request<>>;
stop_callback_for_t<stop_token_of_t<env_of_t<_Receiver>&>, __forward_stop_request>;

inplace_stop_source __stop_source_{};
std::optional<__on_stop> __on_stop_{};
Expand Down Expand Up @@ -127,6 +144,11 @@ namespace experimental::execution
// stop pending operations
__stop_source_.request_stop();
}
__arrive();
}

constexpr void __arrive() noexcept
{
// make __result_ emplacement visible when __count_ goes from one to zero
// This relies on the fact that each sender will call notify() at most once
if (__count_.fetch_sub(1, __std::memory_order_acq_rel) == 1)
Expand Down Expand Up @@ -203,7 +225,7 @@ namespace experimental::execution
void start() & noexcept
{
this->__on_stop_.emplace(get_stop_token(get_env(this->__rcvr_)),
__forward_stop_request{this->__stop_source_});
typename __op_base_t::__forward_stop_request{this});
if (this->__stop_source_.stop_requested())
{
STDEXEC::set_stopped(static_cast<_Receiver&&>(this->__rcvr_));
Expand Down