Calling a thread worker from within a thread worker results in a crash

[davep]

Coming from this question, this reply, and this followup on Discord...

It seems that if you call a thread worker from within a thread worker it results in a crash. This code:

from time import sleep

from textual import on, work
from textual.app import App, ComposeResult
from textual.widgets import Button, Log
from textual.worker import get_current_worker

class WorkerInWorkerApp(App[None]):

    def compose(self) -> ComposeResult:
        yield Button("Start")
        yield Log()

    @work(thread=True)
    def outer(self) -> None:
        worker = get_current_worker()
        for n in range(50):
            if worker.is_cancelled:
                break
            if n == 10:
                self.inner()
            self.call_from_thread(
                self.query_one(Log).write_line,
                f"Outer {n}"
            )
            sleep(0.25)

    @work(thread=True)
    def inner(self) -> None:
        worker = get_current_worker()
        for n in range(50):
            if worker.is_cancelled:
                break
            self.call_from_thread(
                self.query_one(Log).write_line,
                f"Inner {n}"
            )
            sleep(0.25)

    @on(Button.Pressed)
    def start(self) -> None:
        self.outer()

if __name__ == "__main__":
    WorkerInWorkerApp().run()

when run results in this exception:

Task exception was never retrieved
future: <Task finished name='Task-29' coro=<Worker._run() done, defined at /Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py:351> exception=TypeError("'<' not supported between instances of 'WorkerState' and 'WorkerState'")>
Traceback (most recent call last):
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py", line 363, in _run
    self._result = await self.run()
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py", line 347, in run
    return await (
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py", line 317, in _run_threaded
    return await asyncio.get_running_loop().run_in_executor(
  File "/Users/davep/.pyenv/versions/3.10.10/lib/python3.10/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py", line 302, in run_callable
    return work()
  File "/Users/davep/develop/python/textual-sandbox/work_from_work.py", line 21, in outer
    self.inner()
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/_work_decorator.py", line 144, in decorated
    self.run_worker(
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/dom.py", line 270, in run_worker
    worker: Worker[ResultType] = self.workers._new_worker(
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/_worker_manager.py", line 119, in _new_worker
    self.add_worker(worker, start=start, exclusive=exclusive)
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/_worker_manager.py", line 80, in add_worker
    worker._start(self._app, self._remove_worker)
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py", line 391, in _start
    self._task = asyncio.create_task(self._run(app))
  File "/Users/davep/.pyenv/versions/3.10.10/lib/python3.10/asyncio/tasks.py", line 336, in create_task
    loop = events.get_running_loop()
RuntimeError: no running event loop

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/worker.py", line 374, in _run
    app._fatal_error()
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/app.py", line 2000, in _fatal_error
    traceback = Traceback(
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/rich/traceback.py", line 264, in __init__
    trace = self.extract(
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/rich/traceback.py", line 449, in extract
    locals={
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/rich/traceback.py", line 450, in <dictcomp>
    key: pretty.traverse(
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/rich/pretty.py", line 853, in traverse
    node = _traverse(_object, root=True)
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/rich/pretty.py", line 648, in _traverse
    args = list(iter_rich_args(rich_repr_result))
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/rich/pretty.py", line 615, in iter_rich_args
    for arg in rich_args:
  File "/Users/davep/develop/python/textual-sandbox/.venv/lib/python3.10/site-packages/textual/_worker_manager.py", line 46, in __rich_repr__
    for state, count in sorted(counter.items()):
TypeError: '<' not supported between instances of 'WorkerState' and 'WorkerState'
sys:1: RuntimeWarning: coroutine 'Worker._run' was never awaited
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

when the inner worker is called (actually you just get a terminal bell and the app stops doing anything; you see the exception if you break out of the application).

This is easily worked around by running the inner worker with:

self.call_from_thread(self.inner)

which I think I would have done anyway had I been writing the code myself. However, in Discord Will says that it should work as written above; so I'm raising this issue as a thing to investigate further and perhaps make work.

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