NoActiveAppError when DataTable add_column is invoked from worker thread #3927
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When 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 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: |
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Replies: 2 comments 7 replies
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You're trying to manipulate a widget (the |
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Thank you for a quick answer @davep! That's interesting, the same approach works when no worker threads are involved, right? If you have any useful links that would allow to comprehend this matter more I would highly appreciate you sharing it! Do you happen to have any other suggestions for the use-case I've described (creating a big DataTable while keeping application responsive)? |
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I should also have mentioned that you were also sort of violating the rule of doing UI-based things in a non-thread-safe way; so your code will run if you write it like this: 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()
self.call_from_thread(dt.add_column, 'foo')
self.call_from_thread(
lambda: self.mount(Static('DONE!'))
)
if __name__ == '__main__':
app = MyApp()
app.run()(note adding the column in a thread-safe way). You should find all you need on this in the guide entry for the worker API. Personally though: unless I have a very good reason otherwise, I compose in all the widgets I require, and then update them from the thread as per the worker API. |
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Thank you for additional input on this @davep! Is that fair to say that manipulating Widgets from worker thread is inherently unsafe even for not yet mounted widgets? It is unclear for instance why would |
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To quote the documentation:
Adding rows or columns to a DataTable would be calling UI methods. |
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Thank you @davep! To finish this off - what would you recommend as a best practice for loading a relatively big |
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I'd use a worker and call add_row with call_from_thread, or perhaps add_rows in batches; or post the data to add as a message as it gets loaded in by the thread and add it with a handler. |
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I should also have mentioned that you were also sort of violating the rule of doing UI-based things in a non-thread-safe way; so your code will run if you write it like this:
(note adding the column in a th…