#define USE_CORO_VERSION 1 // yields to caller when 1, 
                           // yields to parent when 2 (and crashes after parent exit)

#if USE_CORO_VERSION == 1
    #include <boost/coroutine/all.hpp>
    using coroutine = boost::coroutines::coroutine<void>;
#else
    #include <boost/coroutine2/all.hpp>
    #include <boost/system/config.hpp> // auto-link with Boost.System on Windows
    using coroutine = boost::coroutines2::coroutine<void>;
#endif

#include <iostream>

#include <boost/lockfree/queue.hpp>

boost::lockfree::queue<coroutine::pull_type *> coroutine_queue(1024);

void start_child_coroutine();

void start_parent_coroutine(int params)
{
    // workaround for boost::coroutines2::coroutine<void>::pull_type 
    // not having default constructor
    coroutine::pull_type default_coroutine = coroutine::pull_type(std::move(default_coroutine));

    coroutine::pull_type * pull = 
        new coroutine::pull_type(std::move(default_coroutine));

    *pull = coroutine::pull_type
        (
            [=](coroutine::push_type & yield)
            {
                for (int i = 1; i <= 10; ++i)
                {
                    // if we are in the middle (5th iteration out of 10) 
                    // of parent coroutine - start child coroutine
                    if (i == 5 && params == 1)
                    {
                        start_child_coroutine();
                    }

                    coroutine_queue.push(pull);
                    yield();
                    std::cout << params;
                }
                std::cout << " leaving coroutine " << params << std::endl;
            }
        );
}

void start_child_coroutine()
{
    start_parent_coroutine(2);
}

int main()
{
    start_parent_coroutine(1);

    for (;;)
    {
        coroutine::pull_type * c = nullptr;
        bool got_coroutine = coroutine_queue.pop(c);

        if (got_coroutine)
        {
            std::cout << "g";
            
            (*c)();
            if (!*c) delete c;
        }
        else
        {
            break;
        }
    }
}