You're looking at doing some "event driven programming". The
arriving MQTT messages are telling your system what to do, but as
you grow the system, there will be other sources of events from
sensors, timers, etc. You want to handle these events as quickly as
possible and return control so that you're always responsive to new
events.
That means you need to do the actual processing of the events
outside of callbacks. Typical ways to do this, depending on your
language of choice, are with event loop libraries, threads, and
timers.
defhello():print("hello, world")t=Timer(30.0,hello)t.start()# after 30 seconds, "hello, world" will be printed
Tracking your internal progress as a state machine is a great way to
deal with all of this.
So, basically, in the callback that receives MQTT messages, set a
timer to fire some time later. Keep a reference to the timer, "t",
in case an event arrives indicating that the action should be
canceled before the timer fired. In that case, you call:
t.cancel()
Frank
On 10/5/19 3:10 PM, Carl Karsten wrote:
opps, sorry, I thought this list was specifically for
python-paho.
I'm using Python.
> You basically have to avoid calling sleep
and use timers instead.
this sounds funny asking, but What is a timer?
Years ago I used a gui desktop database app designer, I
dragged a "timer widget" onto the form and type in the
function it should call every X amount of time.
I understand what that did, I understand i need something
like that, but in this context I have no idea how I should
implement it.
I have a few guesses, like check for events in a loop.
maybe add a sleep so the cpu has some cycles to do other
things (no sure what other things are needed, pretty sure
incoming network traffic will take priority? also pretty sure
this is not a problem I should be trying to solve. I am sure
it has been solved 100's of times.
I also guess "event loop" is a thing I need. Which I also
comprehend and could implement one from scratch if I needed
to, but I hope I don't need to.
On Sat, Oct 5, 2019 at 7:32
AM Greg Troxel <gdt@xxxxxxxxxx> wrote:
> When the door opens, the light should stay on for 60
seconds.
> or if the button is pressed, turn the light off 30
seconds later.
> every door open resets the 60 seconds.
>
> (this is the simplified version that I think is the
root of my problem)
This is not an MQTT issue, but I can see it comes up often
in things
that want to use MQTT.
> I can't do "on, sleep(60), off" because that will block
the on_button
> (right?)
If the main control program calls sleep, it will ignore all
other inputs
for that time. So don't do that :-)
> and when the button is pressed, if the door opens again
that should disable
> the "off in 30" thing.
A further complexity is humans asking for lights to be in
certain states
and automatic rules at the same time. In this case I think
you want a
virtual light controlled by the human and a virtual light
controlled by
the rules and the real light to be the OR of those.
> Is there a tutorial page or something I should be
reading?
This is really a fundamental programming issue; you are
constructing a
finite state machine with timers.
There are arguably two approaches to this sort of thing,
usually called
threads and async. It will seems that threads are easier,
but really
they just look easier and async is actually easier, when you
define that
as "work to get a 100% reliable system".
Frameworks that are set up for your problem include