NoActiveAppError when DataTable add_column is invoked from worker thread

[gubenkoved]

When DataTable add_column method is invoked from thread worker application crashes.

I am wondering if this as designed or not? It is understandable that interacting with the application UI elements is inherently not thread safe. I assumed however that creating new widgets in another worker thread is acceptable.

Could someone please clarify on this one?

The use-case I am trying to use it with is following - I am trying to construct a big table and keep application responsive in the mean time, then as soon as table is ready I was going to mount it using call_from_thread.

textual 0.46.0

PS. Thank you for very nice project, it is a pleasure to experiment with!

from textual import work
from textual.app import App
from textual.widgets import Static, DataTable


class MyApp(App):
    def compose(self):
        self.start_work()
        yield Static('HELLO')

    @work(exclusive=True, thread=True)
    def start_work(self):
        dt = DataTable()
        dt.add_column('foo')
        self.call_from_thread(
            lambda: self.mount(Static('DONE!'))
        )


if __name__ == '__main__':
    app = MyApp()
    app.run()

Here is traceback part:

│ .................................................../bug.py:14 in start_work                                          │
│                                                                                                                      │
│   11 │   @work(exclusive=True, thread=True)                                                                          │
│   12 │   def start_work(self):                                                                                       │
│   13 │   │   dt = DataTable()                                                                                        │
│ ❱ 14 │   │   dt.add_column('foo')                                                                                    │
│   15 │   │   self.call_from_thread(                                                                                  │
│   16 │   │   │   lambda: self.mount(Static('DONE!'))                                                                 │
│   17 │   │   )                                                                                                       │
│                                                                                                                      │
│ ╭────────────────────── locals ───────────────────────╮                                                              │
│ │   dt = DataTable()                                  │                                                              │
│ │ self = MyApp(title='MyApp', classes={'-dark-mode'}) │                                                              │
│ ╰─────────────────────────────────────────────────────╯                                                              │
│                                                                                                                      │
│ .................................................../venv/lib/python3.11/site-packages/textual/widgets/_data_table.py │
│ :1491 in add_column                                                                                                  │
│                                                                                                                      │
│   1488 │   │   │   raise DuplicateKey(f"The column key {key!r} already exists.")                                     │
│   1489 │   │   column_index = len(self.columns)                                                                      │
│   1490 │   │   label = Text.from_markup(label) if isinstance(label, str) else label                                  │
│ ❱ 1491 │   │   content_width = measure(self.app.console, label, 1)                                                   │
│   1492 │   │   if width is None:                                                                                     │
│   1493 │   │   │   column = Column(                                                                                  │
│   1494 │   │   │   │   column_key,                                                                                   │
│                                                                                                                      │
│ ╭─────────────── locals ───────────────╮                                                                             │
│ │ column_index = 0                     │                                                                             │
│ │   column_key = ColumnKey(value=None) │                                                                             │
│ │      default = None                  │                                                                             │
│ │          key = None                  │                                                                             │
│ │        label = <text 'foo' []>       │                                                                             │
│ │         self = DataTable()           │                                                                             │
│ │        width = None                  │                                                                             │
│ ╰──────────────────────────────────────╯                                                                             │
│                                                                                                                      │
│ .................................................../venv/lib/python3.11/site-packages/textual/message_pump.py:210 in │
│ app                                                                                                                  │
│                                                                                                                      │
│   207 │   │   │   node: MessagePump | None = self                                                                    │
│   208 │   │   │   while not isinstance(node, App):                                                                   │
│   209 │   │   │   │   if node is None:                                                                               │
│ ❱ 210 │   │   │   │   │   raise NoActiveAppError()                                                                   │
│   211 │   │   │   │   node = node._parent                                                                            │
│   212 │   │   │   active_app.set(node)                                                                               │
│   213 │   │   │   return node                                                                                        │
│                                                                                                                      │
│ ╭───────────── locals ─────────────╮                                                                                 │
│ │  App = <class 'textual.app.App'> │                                                                                 │
│ │ node = None                      │                                                                                 │
│ │ self = DataTable()               │                                                                                 │
│ ╰──────────────────────────────────╯                                                                                 │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯