(Resolved conflict)

LGTM, though I'm slightly unclear on whether this code is upstream to or vendored from https://github.com/we-like-parsers/pegen

The other way around: that code is adapted from the one in CPython.

@pablogsal, would you find it helpful to have mypy run on this code in CI at CPython? I'm not generally involved in maintaining Tools/peg_generator/, so I don't want to merge this unless you'd actually find it useful :)

@pablogsal, would you find it helpful to have mypy run on this code in CI at CPython? I'm not generally involved in maintaining Tools/peg_generator/, so I don't want to merge this unless you'd actually find it useful :)

I think that would be very helpful, indeed, as these types should be up to date 👍

Thanks a lot for the PR @sobolevn and thanks for the review @AlexWaygood

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM Raspbian 3.x has failed when building commit cf7ba83.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/424/builds/4754) and take a look at the build logs.
4. Check if the failure is related to this commit (cf7ba83) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/424/builds/4754

Failed tests:

• test.test_concurrent_futures.test_shutdown

Failed subtests:

• test_interpreter_shutdown - test.test_concurrent_futures.test_shutdown.ProcessPoolForkserverProcessPoolShutdownTest.test_interpreter_shutdown

Summary of the results of the build (if available):

== Tests result: FAILURE then FAILURE ==

443 tests OK.

10 slowest tests:

• test_cppext: 11 min 26 sec
• test_venv: 10 min 2 sec
• test_shelve: 9 min 30 sec
• test_largefile: 9 min 7 sec
• test_math: 4 min 24 sec
• test_compileall: 2 min 30 sec
• test_hashlib: 2 min 13 sec
• test.test_multiprocessing_spawn.test_processes: 2 min 12 sec
• test_peg_generator: 2 min 10 sec
• test_gdb: 1 min 52 sec

1 test failed:
test.test_concurrent_futures.test_shutdown

19 tests skipped:
test.test_asyncio.test_windows_events
test.test_asyncio.test_windows_utils test_devpoll test_idle
test_ioctl test_kqueue test_launcher test_perf_profiler
test_startfile test_tcl test_tkinter test_ttk test_ttk_textonly
test_turtle test_winconsoleio test_winreg test_winsound test_wmi
test_zipfile64

1 re-run test:
test.test_concurrent_futures.test_shutdown

Total duration: 39 min 40 sec

Traceback (most recent call last):
  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/test/test_concurrent_futures/test_shutdown.py", line 49, in test_interpreter_shutdown
    self.assertFalse(err)
AssertionError: b'Exception in thread Thread-1:\nTraceback (most recent call last):\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/threading.py", line 1059, in _bootstrap_inner\n    self.run()\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/concurrent/futures/process.py", line 339, in run\n    self.add_call_item_to_queue()\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/concurrent/futures/process.py", line 394, in add_call_item_to_queue\n    self.call_queue.put(_CallItem(work_id,\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/multiprocessing/queues.py", line 94, in put\n    self._start_thread()\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/multiprocessing/queues.py", line 177, in _start_thread\n    self._thread.start()\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/threading.py", line 978, in start\n    _start_new_thread(self._bootstrap, ())\nRuntimeError: can\'t create new thread at interpreter shutdown\nTraceback (most recent call last):\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/multiprocessing/forkserver.py", line 274, in main\n    code = _serve_one(child_r, fds,\n           ^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/multiprocessing/forkserver.py", line 313, in _serve_one\n    code = spawn._main(child_r, parent_sentinel)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/multiprocessing/spawn.py", line 132, in _main\n    self = reduction.pickle.load(from_parent)\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File "/var/lib/buildbot/workers/3.x.gps-raspbian.nondebug/build/Lib/multiprocessing/synchronize.py", line 115, in __setstate__\n    self._semlock = _multiprocessing.SemLock._rebuild(*state)\n                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\nFileNotFoundError: [Errno 2] No such file or directory\n' is not false