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Merged
dietmarkuehl merged 2 commits into from
Feb 24, 2026
Merged

Stack overflow threadid #224

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6a5ffe2
draft of using the thread ID for the stack overflow management
dietmarkuehl Feb 24, 2026
ef19c00
use thread::id for stackoverflow management
dietmarkuehl Feb 24, 2026
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15 changes: 11 additions & 4 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -59,9 +59,14 @@ ifeq (${hostSystemName},Darwin)

ifeq ($(origin CXX),default)
$(info CXX is using the built-in default: $(CXX))
export CXX=g++-15
CXXLIB=libstdc++
export CXXFLAGS=-stdlib=$(CXXLIB)
ifeq ($(shell uname -m),arm64)
export CXX=clang++
CXXLIB=libc++
else
export CXX=g++-15
CXXLIB=libstdc++
endif
export CXX_FLAGS=-stdlib=$(CXXLIB)
endif
Comment on lines +62 to 70
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Copilot AI Feb 24, 2026

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export CXX_FLAGS=-stdlib=$(CXXLIB) overwrites the existing CXX_FLAGS (e.g., drops -g) and is later overwritten by the SANITIZER-specific CXX_FLAGS = ... assignments, so the stdlib selection can be lost. Also, -stdlib=... is a clang-specific flag; if the else branch selects g++-15, passing -stdlib=libstdc++ via CMAKE_CXX_FLAGS will likely fail. Consider keeping stdlib selection in a separate variable and appending it to CXX_FLAGS, and only adding -stdlib=... when using clang/libc++.

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export GCOV="gcov"
else ifeq (${hostSystemName},Linux)
Expand Down Expand Up @@ -120,6 +125,7 @@ doc:
# NOTE: cmake configure to only test without modules! CK
# ==========================================================
build build-interface:
@echo CXX=$(CXX) CXX_FLAGS=$(CXX_FLAGS)
cmake -G Ninja -S $(SOURCEDIR) -B $(BUILD) $(TOOLCHAIN) $(SYSROOT) \
-D CMAKE_EXPORT_COMPILE_COMMANDS=ON \
-D CMAKE_SKIP_INSTALL_RULES=ON \
Expand All @@ -130,7 +136,8 @@ build build-interface:
-D BEMAN_USE_STD_MODULE=OFF \
-D CMAKE_BUILD_TYPE=Release \
-D CMAKE_SKIP_TEST_ALL_DEPENDENCY=OFF \
-D CMAKE_CXX_COMPILER=$(CXX) --log-level=VERBOSE --fresh
-D CMAKE_CXX_COMPILER=$(CXX) --log-level=VERBOSE --fresh \
-D CMAKE_CXX_FLAGS="$(CXX_FLAGS) $(SAN_FLAGS)"
# XXX -D CMAKE_CXX_FLAGS="$(CXX_FLAGS) $(SAN_FLAGS)"
cmake --build $(BUILD) --target all_verify_interface_header_sets
cmake --build $(BUILD) --target all
Expand Down
17 changes: 12 additions & 5 deletions include/beman/execution/detail/sender_awaitable.hpp
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Expand Up @@ -12,6 +12,7 @@ import std;
#include <concepts>
#include <coroutine>
#include <exception>
#include <thread>
#include <tuple>
#include <type_traits>
#include <utility>
Expand Down Expand Up @@ -53,13 +54,15 @@ class sender_awaitable {
::beman::execution::detail::single_sender_value_type<Sndr, ::beman::execution::env_of_t<Promise>>;
using result_type = ::std::conditional_t<::std::is_void_v<value_type>, unit, value_type>;
using variant_type = ::std::variant<::std::monostate, result_type, ::std::exception_ptr>;
using data_type = ::std::tuple<variant_type, ::std::atomic<bool>, ::std::coroutine_handle<Promise>>;
using data_type = ::std::tuple<variant_type, ::std::atomic<::std::thread::id>, ::std::coroutine_handle<Promise>>;

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std::atomic<std::thread::id> is not guaranteed to be well-formed/portable: std::atomic<T> requires T to be trivially copyable, and std::thread::id is not specified to be. This can fail to compile on some standard libraries. Consider keeping the original std::atomic<bool> state (or using an integral state enum) and store any thread-id info separately if needed.

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struct awaitable_receiver {
using receiver_concept = ::beman::execution::receiver_t;

void resume() {
if (::std::get<1>(*result_ptr_).exchange(true, std::memory_order_acq_rel)) {
std::thread::id id(::std::this_thread::get_id());
if (not ::std::get<1>(*result_ptr_)
.compare_exchange_strong(id, ::std::thread::id{}, std::memory_order_acq_rel)) {
::std::get<2>(*result_ptr_).resume();
}
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This compare_exchange_strong-based gate can resume the coroutine before it has actually suspended: if start(state) causes completion to happen on a different thread before await_suspend executes its CAS, this CAS will fail (thread ids differ) and resume() will call coroutine_handle::resume() while the coroutine is still running, which is undefined behavior. The original atomic<bool> handshake avoided this by only resuming after await_suspend published the suspended state; this should use a proper suspend/completion state machine (e.g., atomic enum/int) rather than comparing thread ids.

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}
Expand All @@ -82,7 +85,9 @@ class sender_awaitable {
}

void set_stopped() && noexcept {
if (::std::get<1>(*result_ptr_).exchange(true, ::std::memory_order_acq_rel)) {
std::thread::id id(::std::this_thread::get_id());
if (not ::std::get<1>(*result_ptr_)
.compare_exchange_strong(id, ::std::thread::id{}, ::std::memory_order_acq_rel)) {
static_cast<::std::coroutine_handle<>>(::std::get<2>(*result_ptr_).promise().unhandled_stopped())
.resume();
}
Expand All @@ -102,14 +107,16 @@ class sender_awaitable {

public:
sender_awaitable(Sndr&& sndr, Promise& p)
: result{::std::monostate{}, false, ::std::coroutine_handle<Promise>::from_promise(p)},
: result{::std::monostate{}, ::std::this_thread::get_id(), ::std::coroutine_handle<Promise>::from_promise(p)},
state{::beman::execution::connect(::std::forward<Sndr>(sndr),
sender_awaitable::awaitable_receiver{::std::addressof(result)})} {}

static constexpr bool await_ready() noexcept { return false; }
::std::coroutine_handle<> await_suspend(::std::coroutine_handle<Promise> handle) noexcept {
::beman::execution::start(state);
if (::std::get<1>(this->result).exchange(true, std::memory_order_acq_rel)) {
::std::thread::id id(::std::this_thread::get_id());
if (not ::std::get<1>(this->result)
.compare_exchange_strong(id, ::std::thread::id{}, ::std::memory_order_acq_rel)) {
if (::std::holds_alternative<::std::monostate>(::std::get<0>(this->result))) {
return ::std::get<2>(this->result).promise().unhandled_stopped();
}
Expand Down