The following code might read errno before calling open... I am happy to be convinced otherwise.

Thanks for the coroutine set.

The evolution of samples from the first one(02.10) to the result is awesome and produces the expected results.
However, what if one would use it from the perspective to write something more generic:

For example the data for "sending coroutine" could be just:

    std::vector<byte> fakeBytes {
        'H'_B, 'e'_B, 'l'_B, 'l'_B, 'o'_B
    };

and the code in "parsing coroutine" is co-awaiting and just co-yielding (echoing):

    while (true) {
        byte b = co_await byte{};
        std::string frame{};
        frame.push_back(static_cast<char>(b));
        co_yield frame;
    }

And in this sense the modified (02.10) keeps working as expected, but already the next one doesn't (is crashed).
Of course, things were done with an eye to a specific version of the protocol, the outcomes in common seem not functionally equivalent. And I thought that the issues could be interesting.

hi, @andreasfertig , thanks for the talk about coroutine in cppcon2022, I profited greatly from your speech. but i find your example given have some running problem when i try to run it, could you pls explain it for me where i did wrong, code are here

#include <coroutine>
#include <list>
#include <iostream>

class Scheduler {
public:
    std::list<std::coroutine_handle<>> m_tasks{};

    bool schedule()
    {
        auto task = m_tasks.front();
        m_tasks.pop_front();

        if (not task.done()) {
            task.resume();
        }
        return not m_tasks.empty();
    }

    auto suspend()
    {
        struct awaiter : std::suspend_always {
            Scheduler &scheduler;

            explicit awaiter(Scheduler s) : scheduler(s)
            {}

            void await_suspend(std::coroutine_handle<> coro) const noexcept
            {
                scheduler.m_tasks.push_back(coro);
            }
        };
        return awaiter{*this};
    }

};

struct Task {
    struct promise_type {
        Task get_return_object()
        {
            return {};
        }

        std::suspend_never initial_suspend() noexcept
        { return {}; }

        std::suspend_never final_suspend() noexcept
        { return {}; }

        void unhandled_exception()
        {}
    };
};


Task taskA(Scheduler &scheduler)
{
    std::cout << "hello, from A" << std::endl;

    co_await scheduler.suspend();

    std::cout << "A is back to work" << std::endl;

    co_await scheduler.suspend();

    std::cout << "A is doing last work" << std::endl;
}

Task taskB(Scheduler &scheduler)
{
    std::cout << "hello, from B" << std::endl;

    co_await scheduler.suspend();

    std::cout << "B is back to work" << std::endl;

    co_await scheduler.suspend();

    std::cout << "B is doing last work" << std::endl;
}

void Use()
{

    Scheduler scheduler{};

    taskA(scheduler);
    taskB(scheduler);

    while (scheduler.schedule()) {}
}

int main()
{
    Use();
    return 0;
}

and my environment are following

➜  ~ uname -a
Darwin HelianthusdeMacBook-Pro.local 21.4.0 Darwin Kernel Version 21.4.0: Fri Mar 18 00:46:32 PDT 2022; root:xnu-8020.101.4~15/RELEASE_ARM64_T6000 arm64
➜  ~ /opt/homebrew/bin/g++-12 -v
Using built-in specs.
COLLECT_GCC=/opt/homebrew/bin/g++-12
COLLECT_LTO_WRAPPER=/opt/homebrew/Cellar/gcc@12/12.1.0_1/bin/../libexec/gcc/aarch64-apple-darwin21/12/lto-wrapper
Target: aarch64-apple-darwin21
Configured with: ../configure --prefix=/opt/homebrew/opt/gcc@12 --libdir=/opt/homebrew/opt/gcc@12/lib/gcc/12 --disable-nls --enable-checking=release --with-gcc-major-version-only --enable-languages=c,c++,objc,obj-c++,fortran --program-suffix=-12 --with-gmp=/opt/homebrew/opt/gmp --with-mpfr=/opt/homebrew/opt/mpfr --with-mpc=/opt/homebrew/opt/libmpc --with-isl=/opt/homebrew/opt/isl --with-zstd=/opt/homebrew/opt/zstd --with-pkgversion='Homebrew GCC 12.1.0_1' --with-bugurl=https://github.com/Homebrew/homebrew-core/issues --with-system-zlib --build=aarch64-apple-darwin21 --with-native-system-header-dir=/usr/include --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX12.sdk
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.1.0 (Homebrew GCC 12.1.0_1)

and i got errors like:

hello, from A
hello, from B
module(19290,0x102e20580) malloc: *** error for object 0x16d4172b8: pointer being freed was not allocated
module(19290,0x102e20580) malloc: *** set a breakpoint in malloc_error_break to debug

Process finished with exit code 134 (interrupted by signal 6: SIGABRT)

The error message is hard to understand.
It seems like type-cast related.
main.cpp:284:1: error: ‘static void promise_type_base<T, G, InitialSuspend>::operator delete(void*, size_t) [with T = std::__cxx11::basic_string<char>; G = generator<std::__cxx11::basic_string<char>, false>; bool InitialSuspend = false]’ called on pointer returned from a mismatched allocation function [-Werror=mismatched-new-delete] 284 | } | ^ 02.25-coroutineParsingDataStreamCustomAllocator1/main.cpp:284:1: note: returned from ‘static void* promise_type_base<T, G, InitialSuspend>::operator new(size_t, arena&, TheRest&& ...) [with TheRest = {DataStreamReader&}; T = std::__cxx11::basic_string<char>; G = generator<std::__cxx11::basic_string<char>, false>; bool InitialSuspend = false]’ /home/wps/cpp20/coro-study/02.25-coroutineParsingDataStreamCustomAllocator1/main.cpp: In function ‘generator<std::byte> sender(arena&, std::vector<std::byte>)’: 02.25-coroutineParsingDataStreamCustomAllocator1/main.cpp:292:1: error: ‘static void promise_type_base<T, G, InitialSuspend>::operator delete(void*, size_t) [with T = std::byte; G = generator<std::byte>; bool InitialSuspend = true]’ called on pointer returned from a mismatched allocation function [-Werror=mismatched-new-delete] 292 | } | ^ 02.25-coroutineParsingDataStreamCustomAllocator1/main.cpp:292:1: note: returned from ‘static void* promise_type_base<T, G, InitialSuspend>::operator new(size_t, arena&, TheRest&& ...) [with TheRest = {std::vector<std::byte, std::allocator<std::byte> >&}; T = std::byte; G = generator<std::byte>; bool InitialSuspend = true]’ cc1plus: all warnings being treated as errors