deadlock detected when trying to start server

Question

I have a simple application where I am using both django and django-rest-framework.

Quite often, when I try to start the local server (python manage.py runserver), I get the following exception:

Watching for file changes with StatReloader
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/project/venv/lib/python3.7/site-packages/django/template/utils.py", line 66, in __getitem__
    return self._engines[alias]
KeyError: 'django'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "/project/venv/lib/python3.7/site-packages/django/utils/autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "/project/venv/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 117, in inner_run
    self.check(display_num_errors=True)
  File "/project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 390, in check
    include_deployment_checks=include_deployment_checks,
  File "/project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 377, in _run_checks
    return checks.run_checks(**kwargs)
  File "/project/venv/lib/python3.7/site-packages/django/core/checks/registry.py", line 72, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/project/venv/lib/python3.7/site-packages/django/contrib/admin/checks.py", line 80, in check_dependencies
    for engine in engines.all():
  File "/project/venv/lib/python3.7/site-packages/django/template/utils.py", line 90, in all
    return [self[alias] for alias in self]
  File "/project/venv/lib/python3.7/site-packages/django/template/utils.py", line 90, in <listcomp>
    return [self[alias] for alias in self]
  File "/project/venv/lib/python3.7/site-packages/django/template/utils.py", line 81, in __getitem__
    engine = engine_cls(params)
  File "/project/venv/lib/python3.7/site-packages/django/template/backends/django.py", line 25, in __init__
    options['libraries'] = self.get_templatetag_libraries(libraries)
  File "/project/venv/lib/python3.7/site-packages/django/template/backends/django.py", line 43, in get_templatetag_libraries
    libraries = get_installed_libraries()
  File "/project/venv/lib/python3.7/site-packages/django/template/backends/django.py", line 108, in get_installed_libraries
    for name in get_package_libraries(pkg):
  File "/project/venv/lib/python3.7/site-packages/django/template/backends/django.py", line 121, in get_package_libraries
    module = import_module(entry[1])
  File "/project/venv/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/project/venv/lib/python3.7/site-packages/rest_framework/templatetags/rest_framework.py", line 15, in <module>
    from rest_framework.renderers import HTMLFormRenderer
  File "/project/venv/lib/python3.7/site-packages/rest_framework/renderers.py", line 20, in <module>
    from django.test.client import encode_multipart
  File "/project/venv/lib/python3.7/site-packages/django/test/client.py", line 23, in <module>
    from django.test import signals
  File "<frozen importlib._bootstrap>", line 980, in _find_and_load
  File "<frozen importlib._bootstrap>", line 149, in __enter__
  File "<frozen importlib._bootstrap>", line 94, in acquire
_frozen_importlib._DeadlockError: deadlock detected by _ModuleLock('django.test.signals') at 4420467792

Performing system checks...

After a couple of retries, the server starts successfully. Therefore, it is not a show-stopper but it is quite annoying.

Since I am quite new to Django, I was wondering if there was a way to prevent such an error.

Answer 1

I had the same issue, I don't know yet how to reproduce it and why it's happening. But it looks like it's something related to the new version of Django.

From this comment on the issue it looks like it's an issue related to .pyc files in the virtual environment.

To fix it this is what I did:

• Deleted all the .pyc files in the project with this command: find . -regex '*.pyc' -delete

• Deactivated the virtual environment and reactivate it.

The issue disappeared

Answer 2

I had the same issue and was unable to reliably reproduce it. I tried removing my .pyc files, but still had the same issues. I moved 'rest_framework' to the end of my list of INSTALLED_APPS and that seems to be working for me.