packio VS Boost.Asio

That's not even helpful, as you usually read/write using composed ops and they will interleave anyway. To have an io object that's capable of correctly pipelining multiple concurrent write- or read-operations, you need a custom strand like this: https://github.com/qchateau/packio/blob/master/include/packio/internal/manual_strand.h

packio, it's an async msgpack-rpc or json-rpc library based on boost.asio

Indeed looks like it, strand_executor_service.hpp is using a Mutex internally (otherwise it wouldn't make sense to me).

as a side note, Asio is also released as an independent library without the boost stuff https://think-async.com/Asio/

Now that vinniefalco is going to kill off the asio standalone (see deprecate standalone ) and only support boost what would people then recommend to switch over to.

The ASIO framework can be found at https://think-async.com/Asio/ and the relevant license for its use is included in the GitHub repository in the Vendor/licenses directory.

The library is found at https://think-async.com/Asio/.

Asio Extracted from the much bigger Boost C++ library, it's apparently a really good networking library. As a bonus it also handles async / threads. Here's a really good video tutorial by OneLoneCoder

Yes: https://github.com/chriskohlhoff/asio/blob/master/asio/include/asio/coroutine.hpp

Here's the main contributor to Asio. I looked at Asio's repository and this was the first guy.