Scene (rule) action ordering during group expansion

[rlkoshak (Rich Koshak)]

@gws

Darn. Ordering IS implied (the scene settings UI has a reorder button!), but it does not explicitly state whether that affects the ordering of the actions or simply the visual layout (okay, it’s the latter)

Technically the commands will be sent to the Items (i.e. placed on the event bus) in order. If you didn’t have that Group, almost all of the time, the Items will get those commands and process them in order. Technically the Items did get the commands in order. But the commands sent to the members of the Group are handled by a different process in parallel.

@gws

Mostly out of curiosity, do you know if there have been any discussions about providing a method for serializing events in a rule like this?

No, it would require a fundamental re-architecting of the event bus and everything that depends on upon the event bus (which is pretty much everything).

@gws

Perhaps you can share how you would handle the problem of ordering actions - (eg, turn receiver on, change input, change volume - but only in that specific order)

If the order matters, the amount of time between the commands also matters. So you’d have to use a rule to sequence the commands with the proper spacing between them. The commands can certainly be sent in order using a scene, but even if they are processed in order, there will be a handful of milliseconds between them which, for all practical purposes is simultaneously.

If using JS or Blockly, this is one of the main uses of OHRT’s Gatekeeper.

var { Gatekeeper } = require('openhab_rules_tools');
var gk = cache.private.get('gatekeeper', () => Gatekeeper());

gk.addCommand(() => items.Receiver.sendCommand('ON'), 'PT5S');
gk.addCommand(() => items.Input.sendCommand('HDMI2', 500);
gk.addCommand(() => items.Volume.sendCommand(25), 0);

The above will command the receiver to ON, wait five seconds, send the command to input ‘HDMI1’, wait half a second, and finally send command 25 to volume.