[zeromq-dev] Mac OS X: test_shutdown_stress sometimes fails

[Dhammika Pathirana]

On Mon, Nov 8, 2010 at 12:13 AM, Martin Sustrik <sustrik at 250bpm.com> wrote:
> Hi Dhammika,
>>
>> zmq_init_t::finalise_initialization() sends attach command to the session.
>> But session::process_attach() can delete this engine, while it's still
>> in use in io_thread out_event() callback.
>>
>>
>
> Can you elaborate on how it can happen? There's engine->unplug() called
> before sending the attach command which should disconnect the engine from
> it's I/O thread.
>


0  zmq::signaler_t::send()
1  zmq::ctx_t::send_command()
2  zmq::object_t::send_command()
3  zmq::object_t::send_term_req()
4  zmq::own_t::terminate()
5  zmq::zmq_init_t::finalise_initialisation()     !-- session deletes
the engine --!
6  zmq::zmq_init_t::read()
7  zmq::encoder_t::message_ready()
8  zmq::encoder_base_t<zmq::encoder_t>::get_data()
9  zmq::zmq_engine_t::out_event()
10  zmq::kqueue_t::loop()
11  zmq::kqueue_t::worker_routine()
12  zmq::thread_t::thread_routine()

In step 9, IO thread is calling engine_t::out_event() callback, and
the engine must be valid for the duration of this call.
But in step 5, session thread receives the engine and deletes it.
Don't you think there's a valid race here?

engine->unplug() does detach the engine, but it only takes effect on
callback return.


Dhammika