Learning asyncio module

[ebolisa]

Hi,

I'm trying to do multitasking using the asyncio module with the following code on a pico w:

import uasyncio
import gc
gc.collect()

async def clock():
    while True:
        t = utime.localtime()
        print("Clock: {:02d}:{:02d}:{:02d}".format(t[3], t[4], t[5]))
        await uasyncio.sleep(1)
    
    
async def temperatures():
    while True:
        gc.collect()
        t = utime.localtime()
        print("Temps: {:02d}:{:02d}:{:02d}".format(t[3], t[4], t[5]))
        await uasyncio.sleep(6)

    
async def main():
    uasyncio.create_task(clock())
    uasyncio.create_task(temperatures())
    while True:
        await clock()
        await temperatures()
    
uasyncio.run(main())

and these are the results:

Clock: 11:41:56
Clock: 11:41:56
Temps: 11:41:57
Clock: 11:41:57
Clock: 11:41:57
Clock: 11:41:58
Clock: 11:41:58
Clock: 11:41:59
Clock: 11:41:59
Clock: 11:42:00
Clock: 11:42:00
Clock: 11:42:01
Clock: 11:42:01
Clock: 11:42:02
Clock: 11:42:02
Temps: 11:42:03
Clock: 11:42:03
Clock: 11:42:03

Apparently, the temperature routine is called every 6 seconds (approx.) but the clock is called twice/second.
Why is that?

TIA

[peterhinch]

You have created two instances of the clock task. create_task creates one, then you await clock() which creates another. The line await temperatures() will never execute because clock (and hence its await) never terminates. Try this, which will create one instance of each:

async def main():
    uasyncio.create_task(clock())
    while True:
        await temperatures()

You might like to look at the uasyncio tutorial.

[ebolisa]

Thank you Peter.
I was following the doc here. Obviously, I didn't understand the process.

[peterhinch]

When the following executes

async def foo():
    await bar()
    do_something()

the do_something() line will only run when bar() terminates. By contrast in

async def foo():
    asyncio.create_task(bar())
    do_something()

bar() runs concurrently. So long as bar() is correctly written as asynchronous code, do_something() will run immediately.

The main() routine is commonly designed never to terminate because if it does, uasyncio terminates and you get back to the REPL.

[ebolisa]

Got it, thanks again.

I had an alarm clock fully controlled/configured by web and running with threads and timers but, it wasn't stable.
This passed weekend, I removed all the timers the threads routines and added the uasyncio module. So far, the clock has been running flawlessly.

[peterhinch]

In general my advice is to use uasyncio in preference to timers, and definitely in preference to threads. Clearly there is a "where possible" caveat. Where you do use timers or threads, it's wise to be clear on exactly what they offer that uasyncio does not.