This issue report is based on a SO question "How to create asyncio stream reader/writer for stdin/stdout?", its answer and comments. Link: https://stackoverflow.com/q/52089869/5378816

The key point is that two unidirectional pipes should be used the same way as one bidirectional network socket. The answer (more precisely the Linux/Unix part of it) and some following comments - both created by highly competent SO members - suggest that FlowControlMixin is a useful class required to write a proper code for this and similar usecases.

That's why the FlowControlMixin or an equivalent should be made available to asyncio programmers as a documented part of the library.

asvetlov: need to handle this usecase with the new API; -1 on exposing FlowControlMixin though.

1. Trio has *stappled* streams for the case, especially useful for starting TLS session over stdin/stdout.
We can master something too.
2. FlowControlMixin was always considered a **private** API. Would be nice to add an underscore prefix to the name if not too late. IIRC the official policy is: if you need the class -- copy and paste it into your project.
3. Even a person with very many stars on StackOverflow doesn't become an asyncio expert automatically; while I very respect the sie and so on.

FlowControlMixing is a private API class.
The class is not intended for the usage outside of asyncio.
If you found it useful for you please feel free to copy-paste the class from asyncio sources into your project.

The reason is: we want to keep freedom for changing asyncio internals without breaking backward compatibility.
One of key technologies for it is keeping the public API as small as possible.

#36889 deprecates using FlowXontrolMixin outside of asyncio