BlockingIOError: [Errno 11] write could not complete without blocking thrown in full screen app with style

[WojciechMigda]

Seen with:

• python 3.6.7
• prompt_toolkit 2.0.9
• aionursery 0.3.0
• asyncio

I have a non-standard architecture, where:

• asyncio loop is run in a separate App class
• main app runs async clients in a nursery:

      async with Nursery() as ns:
          ns.start_soon(self.pull_sink())
          /.../
          ns.start_soon(gui(self, self.loop, self.test_queue))

  gui is an async function where I create prompt toolkit application. I call use_asyncio_event_loop with the loop passed from the parent app. To launch prompt toolkit app I use another nursery context (I will need more concurrent tasks here):

  async with Nursery() as ns:
      ns.start_soon(application.run_async())
      /.../

  where application is prompt toolkit app. In the layout I have TextArea widget, which I initialize with a style for bg and fg colors. When I create prompt toolkit app as full screen it fails:

  Traceback (most recent call last):
    File "/usr/lib/python3.6/asyncio/tasks.py", line 537, in _wrap_awaitable
      return (yield from awaitable.__await__())
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/eventloop/coroutine.py", line 90, in step_next
      new_f = coroutine.throw(exc)
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/application/application.py", line 658, in _run_async2
      result = yield f
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/eventloop/coroutine.py", line 86, in step_next
      new_f = coroutine.send(None)
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/application/application.py", line 601, in _run_async
      self._redraw()
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/application/application.py", line 444, in _redraw
      self.renderer.render(self, self.layout)
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/renderer.py", line 595, in render
      output.flush()
    File "/home/wojtek/.local/lib/python3.6/site-packages/prompt_toolkit/output/vt100.py", line 601, in flush
      out.write(data.encode(self.stdout.encoding or 'utf-8', 'replace'))
  BlockingIOError: [Errno 11] write could not complete without blocking

Interestingly, when I set full_screen setting to False there is no exception thrown, the style is applied to the widget, and the app is running as expected. Also, if I do not apply the style to the widget the app runs fine in full screen mode. Since this is a non-standard usage I tried pulling different string by myself to see if maybe I am doing something wrong that is not mentioned in the docs, but without success. Do you maybe have a hint whether my approach has a bug somewhere or, less likely, prompt toolkit needs a fix? Thank you.

EDIT: Another twist - this error appears only when I launch my python program from within midnight commander. It does not appear within xterm.

[WojciechMigda]

For sure this could be fixed by ignoring also errno.EWOULDBLOCK IOError exceptions here https://github.com/prompt-toolkit/python-prompt-toolkit/blob/master/prompt_toolkit/output/vt100.py#L607