IPython crashing when I hold any key - pthreads

Question

When I ssh into a particular remote machine and start an IPython session, it crashed whenever I hold a key for about half a second (e.g. backspace key).
The error output is pasted below:
File "/home/zach/local/anaconda3/bin/ipython", line 11, in <module>
sys.exit(start_ipython())
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/__init__.py", line 125, in start_ipython
return launch_new_instance(argv=argv, **kwargs)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/traitlets/config/application.py", line 658, in launch_instance
app.start()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/ipapp.py", line 356, in start
self.shell.mainloop()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/interactiveshell.py", line 498, in mainloop
self.interact()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/interactiveshell.py", line 481, in interact
code = self.prompt_for_code()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/interactiveshell.py", line 410, in prompt_for_code
**self._extra_prompt_options())
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 738, in prompt
return run_sync()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 727, in run_sync
return self.app.run(inputhook=self.inputhook, pre_run=pre_run2)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/application/application.py", line 709, in run
return run()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/application/application.py", line 682, in run
run_until_complete(f, inputhook=inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/defaults.py", line 123, in run_until_complete
return get_event_loop().run_until_complete(future, inputhook=inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/posix.py", line 66, in run_until_complete
self._run_once(inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/posix.py", line 85, in _run_once
self._inputhook_context.call_inputhook(ready, inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/inputhook.py", line 78, in call_inputhook
threading.Thread(target=thread).start()
File "/home/zach/local/anaconda3/lib/python3.7/threading.py", line 847, in start
_start_new_thread(self._bootstrap, ())
RuntimeError: can't start new thread
If you suspect this is an IPython bug, please report it at:
https://github.com/ipython/ipython/issues
or send an email to the mailing list at ipython-dev#python.org
You can print a more detailed traceback right now with "%tb", or use "%debug"
to interactively debug it.
Extra-detailed tracebacks for bug-reporting purposes can be enabled via:
%config Application.verbose_crash=True
It drops me from here into a broken bash session where my keystrokes do not appear on screen, although I can execute commands such as ls, man, pwd, ipython, etc. I can only kill the bash session by pressing Control D followed by Control C. In particular, the message's suggestion that I press %tb and so forth is not possible.
Other programs are not competing for threads. Looking through the error, it looks like the an event loop is possibly trying to create a thread to handle every key press, and this eventually causes failure to allocate more threads. It seems a little far-fetched that this would be the issue though since holding a key down is surely expected behavior.
This seems potentially similar to the issue https://ipython.org/faq.html#ipython-crashes-under-os-x-when-using-the-arrow-keys.
It appears not to be a Python issue per se, since if I use Python rather than IPython the issue disappears. I initially used Anaconda ipython but also switched to the system ipython in /usr/bin/ipython with the same results. Also tried a clean install of Anaconda, with the same issue. Also tried a fresh install of Anaconda on a different machine with the same OS, and the issue did not occur.
I am looking for ideas to make progress on this issue. Any ideas are appreciated, and I will post follow-up data if needed.
Python 3.7.3 (default, Mar 27 2019, 22:11:17)
IPython 7.5.0
Ubuntu 18.04.2 LTS

Answer 1

It is fixed now, but still somewhat mysterious to me. I followed the stack trace all the way down through CPython to the pthreads library calls. The pthreads documentation indicated that the error can essentially only arise if one is out of memory on the heap or if the max number of threads has been allocated. I used ulimit to set the virtual memory per process to unlimited (it had been ~3 GB). This resolved the issue.
So apparently the virtual memory limit interfered with the ability to allocate a thread. The obvious solution is that more memory was needed, although it is hard to believe that more than 3 GB is needed to respond to a key press. Another possibility is that the amount allocated per thread is a function of the virtual memory limit--I remember something like that in the pthreads documentation although it was a bit above my head.