Stubgen fails with timeout for locust

Hi,
I'm trying to generate type stubs for Locust and stubgen fails with a timeout (see details below).
I was wondering if someone has any insight into what causes this or how to fix it.

Please provide more information to help us understand the issue:

• Are you reporting a bug, or opening a feature request?
  Bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

  pip install mypy locust
  stubgen -p locust
  

• What is the actual behavior/output?

  Traceback (most recent call last):
  File "./venv/bin/stubgen", line 10, in <module>
      sys.exit(main())
  File "mypy/stubgen.py", line 1564, in main
  File "mypy/stubgen.py", line 1422, in generate_stubs
  File "mypy/stubgen.py", line 1183, in collect_build_targets
  File "mypy/stubgen.py", line 1217, in find_module_paths_using_imports
  File "mypy/stubutil.py", line 62, in walk_packages
  File "mypy/moduleinspect.py", line 137, in get_package_properties
  File "mypy/moduleinspect.py", line 163, in _get_from_queue
  RuntimeError: Timeout waiting for subprocess
  

• What is the behavior/output you expect?
  No console output and generated stubs in out/.

• What are the versions of mypy and Python you are using?

  • Python v3.8.2
  • mypy 0.782

• Do you see the same issue after installing mypy from Git master?
  Yes:

  Traceback (most recent call last):
  File "./venv/bin/stubgen", line 33, in <module>
      sys.exit(load_entry_point('mypy', 'console_scripts', 'stubgen')())
  File "/Users/simon/work/locust-test/mypy/mypy/stubgen.py", line 1564, in main
      generate_stubs(options)
  File "/Users/simon/work/locust-test/mypy/mypy/stubgen.py", line 1422, in generate_stubs
      py_modules, c_modules = collect_build_targets(options, mypy_opts)
  File "/Users/simon/work/locust-test/mypy/mypy/stubgen.py", line 1183, in collect_build_targets
      py_modules, c_modules = find_module_paths_using_imports(options.modules,
  File "/Users/simon/work/locust-test/mypy/mypy/stubgen.py", line 1217, in find_module_paths_using_imports
      found = list(walk_packages(inspect, packages, verbose))
  File "/Users/simon/work/locust-test/mypy/mypy/stubutil.py", line 62, in walk_packages
      prop = inspect.get_package_properties(package_name)
  File "/Users/simon/work/locust-test/mypy/mypy/moduleinspect.py", line 137, in get_package_properties
      res = self._get_from_queue()
  File "/Users/simon/work/locust-test/mypy/mypy/moduleinspect.py", line 163, in _get_from_queue
      raise RuntimeError('Timeout waiting for subprocess')
  RuntimeError: Timeout waiting for subprocess
  

Reproduce the issue with stubgen -p locust after installing mypy and locust. Start at mypy/stubgen.py in collect_build_targets and find_module_paths_using_imports, then follow the calls through mypy/stubutil.py and mypy/moduleinspect.py to the subprocess timeout. Done means the command completes without the timeout and generates stubs in out/.