Throttle property updates in UI

[freaktechnik]

Both my webthing projects have rather high refresh rates on the sensors they expose. That's pretty neat, however the gateway UI has trouble dealing with that. It appears that it tries to re-print all the values every time a single value changes. This leads to it being nearly impossible to change a property from the gateway. It also leads to flicker of the actual property values on the client side, since they are cleared constantly, as the value updates aren't batched in the WoT implementation (and probably the protocol?).

To get reliable operation I have to slow the updates to every couple seconds, depending on the amount of properties that get constant updates. Of course it doesn't make much sense to have a property update every 100ms for binary values, however even a refresh rate of 1 second with 12 properties that are refreshed every second leads to severe flickering, since the properties are updated one after another.

My expectation would be that any property that's not being updated isn't touched and that I can reliably change property values from the gateway while other properties are updating.

[benfrancis]

Thanks for bringing up this issue. I suggest we should do some kind of throttling so the UI is only updated every second or so, and perhaps improve the rendering of the UI elements.

[rzr]

Thx @freaktechnik for reporting this race condition

I am able to reproduce this with:
https://github.com/rzr/mozilla-iot-generic-sensors-adapter/

So I will slow sensor refresh down from 2Hz to 1Hz

I can also explain how to reproduce without sensors.

[freaktechnik]

Based on RzR's issue I'm not sure this is necessarily primarily about speed. It's more about not changing the state of properties that haven't changed in an update. Which is hard to follow, especially for properties that the user can change.

[rzr]

well speed has an effect, to avoid events to cross,

For the record:

<RzR> i think I've found a race condition in notification system
<RzR> UI events could be overridden by non UI updates
<RzR> unsure I am clear, but the effect is like if switch widget is going back to original position just after click
<mrstegeman> yes, that's especially noticeable for slow protocols (like HomeKit)
<RzR> slow of fast ?
<RzR> in sensor I had a refresh rate at 2Hz
<RzR> I am slowing it down to 1
<RzR> if update occurs just after I press the switch off it sets it on and drop the off put
<freaktechnik> oh, that sounds like the "too fast" bug
<freaktechnik> I mean, it has the same issues like https://github.com/mozilla-iot/gateway/issues/1567
<freaktechnik> where some updating properties ruin using non-updating properties
<freaktechnik> (and fast updating properties being unreadable)
<RzR> yea