Re: [asio-users] Segfault on read_op

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

Hi there,

Just a quick followup on this problem, in case someone else encounters 
it. I used a memory analyzer and traced the bug. I found and fixed the 
segmentation fault.

I feel really stupid, I forgot to add

#define ASIO_HAS_THREADS
#define ASIO_WINDOWS

before including the asio header. That messed up multithreaded 
operations - caused some uninitialised reads which in turn caused the 
access violation.

I am happy to say that the network part of my application seems to work 
well now.

Cheers,
Benjamin

On 05.09.2017 13:58, Benjamin Richner wrote:
> 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
>
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