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The design I want seems like fairly basic:

struct my_object {
  explicit my_object(io_context& ctx)
   : strand{make_strand(ctx)} 
  {
     socket = make_unique<some_socket_like_object>(*strand);
  } 

  void my_api() { 
   // Various async operations are launched through the socket
   // which end up on the strand. They use some_data, this, etc.
  }

  ~my_object() { 
    // finish all outstanding async operations that 
    // may access "some_data", "this" etc.
 
    // delete the strand 
    strand.reset();
  }

private:
  // my class's data:
  unique_ptr<socket> socket;
  data some_data;
  cancellation_signal some_cancellation;
  // etc...

  // strand will be deleted first
  optional<strand<...>> strand;
};

What is a completely run-of-the mill behaviour in any async framework seems like an absolutely infeasible design with asio and I struggle to understand why it seems to fight so hard against the concept of encapsulation.
Even with doing things such as this in the dtor:

std::future<void> wait = boost::asio::dispatch(
  boost::asio::bind_executor(
    *m_strand
  , std::packaged_task<void()>([] { /* cleanup */; }) 
  )
); 
wait.get();

and putting the strand in a std::optional to control its deletion time explicitly, I still get tasks or completion handlers running in my io_context and referencing said strand after it and all the objects putting work on it were deleted:

~my_object() { 
  std::future<void> wait = boost::asio::dispatch(
    boost::asio::bind_executor(
      *m_strand
    , std::packaged_task<void()>([this] { 
        // cleanup
        socket.reset(); 
        some_cancellation.emit(boost::asio::cancellation_type::all);
      }) 
    )
  ); 
  
  // Make sure that we get to a point where the socket object has been deleted and cannot submit new tasks ever: 
  wait.get();

  // Make sure that the strand gets cleared
  m_strand.reset(); 

  // Here the io_context still has some tasks running that were put on the strand, accessing for instance !
}

e.g. later on:

    #0 0x8010e64 in boost::asio::cancellation_slot::clear() /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/impl/cancellation_signal.ipp:42:24
    #1 0x8118d48 in void async_mqtt5::detail::cancellable_handler<boost::asio::detail::as_tuple_handler<boost::asio::detail::awaitable_handler<boost::asio::any_io_executor, std::tuple<boost::system::error_code, std::vector<async_mqtt5::reason_code, std::allocator<async_mqtt5:2
    #2 0x8118d48 in async_mqtt5::detail::subscribe_op<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>, boost::asio::detail::as_tuple_handler<boost::asio::detail::awaitable_handler<boost:2
    #3 0x8118238 in async_mqtt5::detail::subscribe_op<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>, boost::asio::detail::as_tuple_handler<boost::asio::detail::awaitable_handler<boost:1
    #4 0x8117b44 in void boost::asio::detail::prepend_handler<async_mqtt5::detail::subscribe_op<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>, boost::asio::detail::as_tuple_handler<boo5
    #5 0x8117b44 in void boost::asio::detail::prepend_handler<async_mqtt5::detail::subscribe_op<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>, boost::asio::detail::as_tuple_handler<boo1
    #6 0x8117b44 in void boost::asio::detail::any_completion_handler_impl<boost::asio::detail::prepend_handler<async_mqtt5::detail::subscribe_op<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::mono5
    #7 0x804d374 in boost::asio::detail::any_completion_handler_call_fn<void (boost::system::error_code)>::call(boost::asio::detail::any_completion_handler_impl_base*, boost::system::error_code) const /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/a5
    #8 0x804d374 in decltype((*this).fn_table_->call((*this).impl_, static_cast<boost::system::error_code&>(fp))) boost::asio::any_completion_handler<void (boost::system::error_code)>::operator()<boost::system::error_code&>(boost::system::error_code&) /home/jcelerier/ossia/sc5
    #9 0x8044fe8 in async_mqtt5::detail::write_req::complete(boost::system::error_code) /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/async-mqtt5/include/async_mqtt5/impl/async_sender.hpp:47:3
    #10 0x8044fe8 in async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>::operator()(std::vector<async_mqtt5::detail::write_req, boost::asio::recycling_all7
    #11 0x80449b8 in void std::__invoke_impl<void, async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>&, std::vector<async_mqtt5::detail::write_req, boost:4
    #12 0x80439c0 in std::__invoke_result<async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>&, std::vector<async_mqtt5::detail::write_req, boost::asio::re4
    #13 0x80439c0 in std::__invoke_result<async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>&, std::vector<async_mqtt5::detail::write_req, boost::asio::re1
    #14 0x80439c0 in void boost::asio::detail::prepend_handler<std::reference_wrapper<async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>>, std::vector<asy5
    #15 0x80439c0 in void boost::asio::detail::prepend_handler<std::reference_wrapper<async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>>, std::vector<asy1
    #16 0x80439c0 in boost::asio::result_of<boost::asio::detail::prepend_handler<std::reference_wrapper<async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, std::monostate>>2
    #17 0x80439c0 in boost::asio::result_of<boost::asio::executor_binder<boost::asio::detail::prepend_handler<std::reference_wrapper<async_mqtt5::detail::async_sender<async_mqtt5::detail::client_service<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_i2
    #18 0x80439c0 in async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, async_mqtt5::detail::stream_context<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::a3
    #19 0x80439c0 in async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, async_mqtt5::detail::stream_context<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::ap
    #20 0x80b6720 in void boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, async_mqtt5::detail::stream_context<boost::asio::basic_st5
    #21 0x80b6aa4 in void boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, async_mqtt5::detail::stream_context<boost::asio::basic_st1
    #22 0x80b6aa4 in boost::asio::detail::binder0<boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, async_mqtt5::detail::stream_conte5
    #23 0x80b6aa4 in void boost::asio::detail::executor_function::complete<boost::asio::detail::binder0<boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asi7
    #24 0x786aa84 in boost::asio::detail::executor_function::operator()() /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/executor_function.hpp:61:7
    #25 0x786aa84 in void boost::asio::detail::strand_executor_service::do_execute<boost::asio::io_context::basic_executor_type<std::allocator<void>, 4ul> const, boost::asio::detail::executor_function, std::allocator<void>>(std::shared_ptr<boost::asio::detail::strand_executor5
    #26 0x786a700 in void boost::asio::detail::strand_executor_service::execute<boost::asio::io_context::basic_executor_type<std::allocator<void>, 4ul> const, boost::asio::detail::executor_function>(std::shared_ptr<boost::asio::detail::strand_executor_service::strand_impl> co0
    #27 0x786a700 in boost::asio::constraint<traits::execute_member<boost::asio::io_context::basic_executor_type<std::allocator<void>, 4ul> const&, boost::asio::detail::executor_function>::is_valid, void>::type boost::asio::strand<boost::asio::io_context::basic_executor_type<5
    #28 0x786a700 in void boost::asio::execution::detail::any_executor_base::execute_ex<boost::asio::strand<boost::asio::io_context::basic_executor_type<std::allocator<void>, 4ul>>>(boost::asio::execution::detail::any_executor_base const&, boost::asio::detail::executor_functi8
    #29 0x80b5eac in void boost::asio::execution::detail::any_executor_base::execute<boost::asio::detail::binder0<boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, 9
    #30 0x80b5aac in boost::asio::detail::work_dispatcher<boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, async_mqtt5::detail::stre5
    #31 0x80b7160 in void boost::asio::detail::executor_function::complete<boost::asio::detail::work_dispatcher<boost::asio::detail::prepend_handler<async_mqtt5::detail::write_op<async_mqtt5::detail::autoconnect_stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, bo7
    #32 0x3a8a290 in boost::asio::detail::executor_function::operator()() /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/executor_function.hpp:61:7
    #33 0x3a8a290 in boost::asio::detail::executor_op<boost::asio::detail::executor_function, std::allocator<void>, boost::asio::detail::scheduler_operation>::do_complete(void*, boost::asio::detail::scheduler_operation*, boost::system::error_code const&, unsigned long) /home/7
    #34 0x7866a14 in boost::asio::detail::scheduler_operation::complete(void*, boost::system::error_code const&, unsigned long) /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/scheduler_operation.hpp:40:5
    #35 0x7866a14 in boost::asio::detail::strand_executor_service::run_ready_handlers(std::shared_ptr<boost::asio::detail::strand_executor_service::strand_impl>&) /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/impl/strand_executor_servic8
    #36 0x78680d0 in boost::asio::detail::strand_executor_service::invoker<boost::asio::io_context::basic_executor_type<std::allocator<void>, 0ul> const, void>::operator()() /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/impl/strand_exec5
    #37 0x78680d0 in boost::asio::detail::executor_op<boost::asio::detail::strand_executor_service::invoker<boost::asio::io_context::basic_executor_type<std::allocator<void>, 0ul> const, void>, boost::asio::detail::recycling_allocator<void, boost::asio::detail::thread_info_ba7
    #38 0x2b5ca68 in boost::asio::detail::scheduler_operation::complete(void*, boost::system::error_code const&, unsigned long) /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/scheduler_operation.hpp:40:5
    #39 0x2b5ca68 in boost::asio::detail::scheduler::do_run_one(boost::asio::detail::conditionally_enabled_mutex::scoped_lock&, boost::asio::detail::scheduler_thread_info&, boost::system::error_code const&) /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/b2
    #40 0x2b5bdf8 in boost::asio::detail::scheduler::run(boost::system::error_code&) /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/detail/impl/scheduler.ipp:210:10
    #41 0x2b5f844 in boost::asio::io_context::run() /home/jcelerier/ossia/score/3rdparty/libossia/3rdparty/boost_1_85_0/boost/asio/impl/io_context.ipp:64:24

What must I do to make sure all the tasks are all completely processed and will never put any new task on the io_context at some point in my dtor ?

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boost asio: how to encapsulate strand properly