How to turn system monitor script into a app?

[HugoP]

Hi, I'm new to wave and started running some of the tutorials but I'm stuck with turning a script into a app.

The script in question is the system_monitor example.

How can I turn this into a non blocking app?

Any help will be appreciated.

[mturoci]

cc @marek-mihok

[marek-mihok]

The answer lies in unblocking psutil.cpu_percent() by removing its interval=1 parameter and using asynchronous q.sleep instead of synchronous time.sleep. You can see it's non-blocking on this counter app:

Screen.Recording.2024-03-20.at.17.22.37.mov

import psutil

from h2o_wave import main, app, Q, ui, data

async def monitor_cpu(q: Q):
    while True:
        await q.sleep(1)
        cpu_usage = psutil.cpu_percent()
        q.page['monitor'].value = cpu_usage
        q.page['monitor'].data.usage = cpu_usage
        q.page['monitor'].plot_data[-1] = [q.client.tick, cpu_usage]
        q.client.tick += 1    
        await q.page.save()

@app('/monitor')
async def serve(q: Q):
    if not q.client.initialized:
        q.client.tick = 0
        q.client.count = 0
        q.page['monitor'] = ui.small_series_stat_card(
            box='1 1 1 1',
            title='CPU',
            value='={{usage}}%',
            data=dict(usage=0.0),
            plot_data=data('tick usage', -15),
            plot_category='tick',
            plot_value='usage',
            plot_zero_value=0,
            plot_color='$red',
        )
        q.page['counter'] = ui.form_card(box='2 1 2 2', items=[
            ui.text(name='text', content=f'Current count: {q.client.count}'),
            ui.button(name='increment', label='Increment'),
        ])
        q.client.initialized = True 
        await monitor_cpu(q)

    if q.args.increment:
        q.client.count += 1
        q.page['counter'].text.content = f'Current count: {q.client.count}'
    
    await q.page.save()

If you struggle with unblocking your apps in the future this article by @mturoci may be helpful.

[HugoP]

That's great, thanks.

[HugoP]

Am I correct that all wave app's need to be run with --no-reload to avoid getting stuck at Waiting for background tasks to complete?

INFO:     Shutting down
INFO:     Waiting for background tasks to complete. (CTRL+C to force quit)

[mturoci]

--no-reload means it doesn't watch for file changes to restart the server. If you do not want to wait for background tasks to complete, check uvicorn docs to see whether it's possible.