Accidentally nonblocking
Cory Benfield's PyCon talk last week, "Building Protocol Libraries the Right Way" (https://www.youtube.com/watch?v=7cC3_jGwl_U), makes the argument that a large number of problems can be traced to not cleanly separating responsibilities of actually physically doing I/O and making semantic sense of the bytes. His primary worry was about reimplementing things like HTTP many times, once for each I/O framework (why do Twisted, Tornado, and asyncio all have their own HTTP implementation?). But it seems the same problem can be seen here: every single part of the code thinks it knows how to actually retrieve data from the network, so it interacts with the network on its own, causing nested polling and similar awkwardness. If every part of the event-processing code thinks it knows how to do network I/O, you have many more opportunities for getting network I/O wrong.If xterm were designed so that e.g. xevents() had only the responsibility of fetching bytes from the X socket and do_xevents() and everything else had only the responsibility of handling bytes from an buffer, there would be no temptation to poll in two different functions. Only one function would even know that the byte source is a socket; the rest just know about the buffer.