segfault in stdexec::__shared::__shared_state for many split with gcc #1743
Description
Having more than one split does not work will gcc (using 71d22ca).
For the code snippet, see below dockerfile.
I tried with gcc 12, 13, and 14: it always compiles, and always segfaults (see below trace).
It's fine with clang 21.
Here is the output for g++-14
Program received signal SIGSEGV, Segmentation fault.
0x00005a14be8701fb in stdexec::__shared::__shared_state<stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#7}{}>, stdexec::__env::env<> >::__inc_ref() ()
#0 0x00005a14be8701fb in stdexec::__shared::__shared_state<stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#7}{}>, stdexec::__env::env<> >::__inc_ref() ()
#1 0x00005a14be86f8bd in _ZN7stdexec8__shared5__boxINS_12_GLOBAL__N_17__sexprIXtlNS_UlvE5_EEEEENS_5__env3envIJEEELb1EEC2ERKS9_QT1_ ()
#2 0x00005a14be86d88d in stdexec::__detail::__captures<stdexec::__split::__split_t, stdexec::__shared::__box<stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#7}{}>, stdexec::__env::env<>, true> >(stdexec::__split::__split_t, stdexec::__shared::__box<stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#7}{}>, stdexec::__env::env<>, true>&&)::{lambda<typename $T0, typename $T1>($T0, $T1&&)#1}::__captures({lambda<typename $T0, typename $T1>($T0, $T1&&)#1} const&) ()
#3 0x00005a14be86d8b3 in stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#9}{}>::__sexpr(stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#9}{}> const&) ()
#4 0x00005a14be86d8ec in auto stdexec::__then::then_t::operator()<stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#9}{}>&, main::{lambda()#2}>(stdexec::(anonymous namespace)::__sexpr<stdexec::{lambda()#9}{}>&, main::{lambda()#2}) const ()
#5 0x00005a14be86f2b3 in main ()
A debugging session is active.Use the dockerfile with the following command to see what's going on:
docker buildx build --tag=test --progress=plain - < dockerfile && docker run --rm -it test bash -c "gdb -ex run -ex bt -ex quit ./a.out"
ARG COMPILER=gcc
# Base requirements.
FROM ubuntu:24.04 AS base
RUN apt update
RUN apt --yes --no-install-recommends install git ca-certificates git wget lsb-release gpg software-properties-common gdb
RUN git clone --branch=main https://github.com/NVIDIA/stdexec
RUN cd stdexec && git checkout 71d22ca77d5a1eb2b107ed2c8db6cbea90f70c68
# Install GCC.
FROM base AS gcc
ARG GCC_VERSION=14
RUN apt --yes --no-install-recommends install g++-${GCC_VERSION}
# Install Clang.
FROM base AS clang
ARG CLANG_VERSION=21
RUN <<EOF
set -ex
wget https://apt.llvm.org/llvm.sh
chmod +x llvm.sh
./llvm.sh ${CLANG_VERSION}
rm llvm.sh
apt --yes --no-install-recommends install clang-${CLANG_VERSION}
EOF
# Let's try out.
FROM ${COMPILER}
COPY <<EOF test_when_all.cpp
#include <iostream>
#include "stdexec/execution.hpp"
#define THEN_SHOW_ID ::stdexec::then([]() -> void { std::cout << std::this_thread::get_id() << std::endl; })
int main()
{
::stdexec::inline_scheduler scheduler{};
auto fork_A = ::stdexec::schedule(scheduler)
| THEN_SHOW_ID
| ::stdexec::split();
auto chain_A = ::stdexec::when_all(
fork_A | THEN_SHOW_ID,
std::move(fork_A) | THEN_SHOW_ID
);
auto fork_B = std::move(chain_A)
| ::stdexec::continues_on(scheduler)
| ::stdexec::split();
auto chain_B = ::stdexec::when_all(
fork_B | THEN_SHOW_ID,
std::move(fork_B) | THEN_SHOW_ID
);
::stdexec::sync_wait(std::move(chain_B));
}
EOF
RUN g++-14 --version
RUN g++-14 -Wall -Wextra -Werror -std=c++20 -I/stdexec/include test_when_all.cpp
CMD ./a.out