Could not unblock the boost asio acceptor

Question

I am trying to cancel a TCP acceptor by the programs keeps blocked in that line.

One thread waits for connections like this:

boost::system::error_code ec;
acceptor_ = new boost::asio::ip::tcp::acceptor(io_service_, boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), port));
acceptor_->accept(socket_, ec);  // socket_ is a boost::asio::ip::tcp:socket

The thread that must close the acceptor does:

boost::system::error_code ec;
acceptor_->close(ec);

Is there something I am missing? I am not using any async operation, so may I do something with the io_service object?

You could try using `acceptor_->cancel();` before closing it. I'm using that in my program and it works fine. However I think `close()` should also work. Are you sure you are working on the same acceptor object? — Matthias247, Aug 05 '14 at 10:58
Yes, same acceptor of course. My code works on Windows but not on Linux, any ideas? — Didac Perez Parera, Aug 05 '14 at 13:28
What is the stack trace when `close()` blocks? Why are you canceling from [another thread](http://www.boost.org/doc/libs/1_55_0/doc/html/boost_asio/reference/ip__tcp/acceptor.html)? — Sam Miller, Aug 05 '14 at 17:22
Why can not cancel the acceptor from another thread? I mean, if accept is a blocking operation, how can I cancel it from the same thread? — Didac Perez Parera, Aug 06 '14 at 07:27

score 1 · Answer 1 · edited May 23 '17 at 11:52

In short, you cannot cancel most of async operations using asio function and methods.

The problem is underlying accept, read etc are system calls. They cannot be interrupted using io_service::stop or cancel since accepting thread is blocked inside syscall, not asio event loop. They only can be interrupted by killing thread or sending a signal.

I'd prefer to make this acceptor asyncronous, so problem will gone. Also see this Q on SO about this

Could not unblock the boost asio acceptor

1 Answers1