State does not get edited in long lasting (background) tasks about reflex

[masenf]

You really do not want to block in a background task.

Because reflex is an async-based framework, any non-async functions that are long running will block the whole server from processing other requests, sending deltas, etc.

If you need to execute blocking code in reflex, then you can farm it out to a separate process or thread and monitor the result in the background task.

In your code example above, you'll notice that if you open a second tab and try to click the button it actually wont do anything while the first tab is crunching along.

For simple stuff, you can use await asyncio.get_event_loop().run_in_executor(my_func) to run the function in a thread and await the result.

For heavier or CPU-bound tasks, then you can run with a process pool. Here's some example

from __future__ import annotations

import asyncio
import multiprocessing
import multiprocessing.pool
import time

import reflex as rx


_global_pool: multiprocessing.Pool | None = None


class State(rx.State):
    var: str = "Not Started"

    def _pool(self) -> multiprocessing.Pool:
        global _global_pool
        if _global_pool is None:
            _global_pool = multiprocessing.Pool()
        return _global_pool

    @rx.background
    async def slow_task(self):
        start_time = time.time()
        async_result = self._pool().apply_async(time.sleep, (60,))
        async with self:
            self.var = "Working..."
        print("Dispatched task to process pool")

        # wait for the task to complete
        while not async_result.ready():
            await asyncio.sleep(1)

        print(f"elapsed time: {time.time() - start_time}")
        print(f"result: {async_result.get()}")
        async with self:
            self.var = "Done!"


def index() -> rx.Component:
    return rx.container(
        rx.vstack(
            rx.button("Run slow task", on_click=State.slow_task),
            rx.text(f"Status: {State.var}"),
            align="center",
        ),
    )


app = rx.App()
app.add_page(index)

[NotAnyMike]

Thank you for your answer, I will give it a try and get back to you!

[NotAnyMike]

Your idea worked great. thanks for suggesting it!