OSError Bad file descriptor

Hello,

Encounter OSError when using prompt-toolkit in xonsh:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xonsh/ptk/shortcuts.py", line 108, in prompt
    document = cli.run(reset_current_buffer=False)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prompt_toolkit/interface.py", line 394, in run
    self.eventloop.run(self.input, self.create_eventloop_callbacks())
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prompt_toolkit/eventloop/posix.py", line 93, in run
    self.add_reader(self._schedule_pipe[0], None)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prompt_toolkit/eventloop/posix.py", line 280, in add_reader
    self.selector.register(fd)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prompt_toolkit/eventloop/select.py", line 75, in register
    sel.register(fd)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prompt_toolkit/eventloop/select.py", line 130, in register
    self._sel.register(fd, selectors.EVENT_READ, None)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/selectors.py", line 536, in register
    self._kqueue.control([kev], 0, 0)
OSError: [Errno 9] Bad file descriptor

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.5/bin/xonsh", line 3, in <module>
    main()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xonsh/main.py", line 276, in main
    shell.shell.cmdloop()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xonsh/ptk/shell.py", line 132, in cmdloop
    line = self.singleline(auto_suggest=auto_suggest)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xonsh/ptk/shell.py", line 101, in singleline
    line = self.prompter.prompt(**prompt_args)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xonsh/ptk/shortcuts.py", line 113, in prompt
    eventloop.close()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/prompt_toolkit/eventloop/posix.py", line 270, in close
    os.close(schedule_pipe[0])
OSError: [Errno 9] Bad file descriptor

Was running a command like cat foo.json | py -m json.tool. Cannot reproduce it anymore. Could it be an issue on PTK side?

Start with the traceback paths in prompt_toolkit/eventloop/posix.py and prompt_toolkit/eventloop/select.py, then inspect how the schedule pipe is created, registered, and closed during the reported xonsh command. Reproduce the piped cat foo.json | py -m json.tool scenario if possible and determine whether the file descriptor failure is in prompt-toolkit. Done means the failure is explained and covered by a regression test or the report is confirmed unreproducible.