High CPU usage with run_async

[johanfforsberg]

Hi!

I just checked back on this project and noticed that there is now integrated support for asyncio, which should make my usage a lot easier.

However when trying it, I find that the CPU usage is very high, approaching 100% of a core even if the application is doing little work apart from rendering. For example it happens with a slightly modified plotting example from the docs:

import asyncio

import numpy as np
from imgui_bundle import imgui, implot, imgui_md, hello_imgui, immapp


def gui():
    # Render Markdown text
    imgui_md.render_unindented("""
    # Render an animated plot with ImPlot
     This example uses `ImPlot` for real-time plotting, and `imgui_md` for markdown.
    """)

    # Render an animated plot (updates every frame)
    if implot.begin_plot(
            title_id="Plot",
            # size in em units (1em = height of a character)
            size=hello_imgui.em_to_vec2(40, 20)):
        x = np.arange(0, np.pi * 4, 0.01)
        y = np.cos(x + imgui.get_time())
        implot.plot_line("y1", x, y)
        implot.end_plot()

    if imgui.button("Exit"):
        hello_imgui.get_runner_params().app_shall_exit = True


# Run the app with ImPlot and markdown support
asyncio.run(
    immapp.run_async(
        gui,
        with_implot=True,
        with_markdown=True,
        window_size=(700, 500)))

CPU usage with the non-async version is ~15%.

I'm on Debian trixie, used python 3.13 and 3.14 (installed with uv), and imgui_bundle 1.92.601.

Thanks for your work!

[pthom]

Hi @johanfforsberg

Thanks a lot for your report!
You are right, there was an issue:

The old implementation did:

       while not hello_imgui.get_runner_params().app_shall_exit:
            manual_render.render()
            await asyncio.sleep(0)

where manual_render.render() exits early when no rendering is needed: this is enough to be compatible with async usage.

However, this tight loop can still eat CPU, since asyncio.sleep(0) does not "sleep" enough.

The new implementation does:

        while not hello_imgui.get_runner_params().app_shall_exit:
            manual_render.render()
            # wait_time provided by C++ side
            wait_time = hello_imgui._priv_idle_frame_wait_duration_for_python_async_io()
            if wait_time > 0.0:
                await asyncio.sleep(wait_time)
            else:
                await asyncio.sleep(0)

On my side, this did reduce the CPU usage a lot.

[pthom]

This will be included in the release v1.92.700 which is due tomorrow (if all goes well).

Please keep me updated after the release :-)

[johanfforsberg]

Great, I don't see a new release yet, but I tried installing the main branch after your changes, and it indeed seems to solve the issue. Thanks in advance!

[pthom]

v1.92.700 is out!

[johanfforsberg]

Looks good to me, I think you can close this.