Re: [asio-users] Segfault on read_op

[Benjamin R. <be...@bl...>]

Hi asio users

I took all your recommendations, read up on how asio works and rebuilt 
my networking class. I posted/wrapped every single operation on a socket 
into its corresponding strand (one strand per socket) and I used shared 
pointers for all lambdas and bound functions to make sure the object 
does not go out of scope.

However, now I get segmentation faults. It seems to be caused by a 
pending async_read when the socket gets shut down by the remote machine 
(I would expect my receive callback to be called with EOF error, but I 
get a segfault instead). This happens before my callback is called, 
inside asio. Now, I am really at my wit's end. I do not know how I 
should debug this. I feel like I am using the asio API correctly:

auto self(shared_from_this());//Important! Prevents this object from 
being deleted.
strand.post(
[this, self]
{
asio::async_read(self->socket, asio::buffer(header_buffer), 
strand.wrap(std::bind(on_received, shared_from_this(), 
std::placeholders::_1, std::placeholders::_2)));
});

All the other async operations and calls on socket functions are posted 
and wrapped in a similar way. I also verified that the object still 
exists (the destructor has not run yet). It seems to be a multithreading 
problem though because I cannot reproduce it with just 1 worker thread.

The function where it segfaults is inside asio\detail\call_stack.hpp, 
line 92: contains()
And that function was called by asio\detail\impl\strand_service.hpp, 
line 54: 
dispatch<asio::detail::rewrapped_handler<asio::detail::binder2<asio::detail::read_op<asio::basic_stream_socket<asio::ip::tcp>, 
asio::mutable_buffers_1, asio::detail::transfer_all_t, 
asio::detail::wrapped_handler<asio::io_service::strand, 
std::_Bind<std::_Mem_fn<void (TCP_Socket_Impl::*)(const 
std::error_code&, unsigned int)>(std::shared_ptr<TCP_Socket_Impl>, 
std::_Placeholder<1>, std::_Placeholder<2>)>, 
asio::detail::is_continuation_if_running> >, std::error_code, unsigned 
int>, std::_Bind<std::_Mem_fn<vo...

Does anyone have an idea? Thanks for your time.

Cheers,
Benjamin