Assertion fail / stack-buffer-underflow: catch all exception handler gets called on coroutine destruction

[StephanDollberg]

Hello,

I am not sure whether this is a boost::asio or boost::coroutine bug but I thought I'd start here as it doesn't really seem related to any asio code. Happy to report it to boost::asio though!

the following code:

#include <iostream>
#include <chrono>

#include <boost/asio/io_context.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/asio/steady_timer.hpp>

int main(int argc, char* argv[]) {
    boost::asio::io_context io_context;

    boost::asio::spawn(io_context, [&] (boost::asio::yield_context yield) {
        boost::asio::steady_timer timer(io_context);
        
        while (true) {
            try {
                std::cout << "before" << std::endl;
                timer.expires_after(std::chrono::seconds(1));
                timer.async_wait(yield);
                std::cout << "after" << std::endl;
            }
            catch (...) {
                std::cout << "excep handler" << std::endl;
            }
        }
    });

    for (int i = 0; i < 1; ++i) {
        io_context.run_one();
    }

    std::cout << "done" << std::endl;

    return 0;
}

gives the following output:

before
done
excep handler
before
bastelbox: /usr/include/boost/coroutine/detail/push_coroutine_impl.hpp:252: void boost::coroutines::detail::push_coroutine_impl::unwind_stack(): Assertion `is_complete()' failed.
Aborted (core dumped)

It seems like when the coroutine handler gets destroyed (once the io_context gets destroyed) execution is resumed in the catch all exception handler. Using a non-catch all handler like only catching std::exception results in normal behaviour (only before and done is printed).

I am testing this with g++ 8 and boost 1.69. I can reproduce it in both -O0 and -O2. Enabling ASAN also results in a stack-buffer-underflow warning: https://gist.github.com/StephanDollberg/a1ab914d806d3aa4406c5cf840dd2e00

Thanks,
Stephan

[olk]

you must not catch detail::forced_unwind exception as you do with catch(...) - the exception is used for unwinding the stack - see section exceptions at https://www.boost.org/doc/libs/1_69_0/libs/coroutine/doc/html/coroutine/coroutine/asymmetric.html