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Python How to run two processes at the same time with asyncio

How to run send_data() and read_data() at the same time in asyncio?

You can't use run() to start two processes at the same time in asyncio. run() starts one process and it waits for its end - so run(send_data()) starts function send_data and it waits for its end - and this way it never runs read_data. If you change order then run(read_data()) will wait for end of read_data and it will never run send_data

You can use use run() to start one function which uses create_task() for send_data() and read_data(). You have to first create tasks and later use them with await because in other way it doesn't start second function read_data.

In example in both functions I use asyncio.sleep() to have some functions with await.

import queue
import asyncio
import datetime

data_queue = queue.Queue()

async def send_data():
    print("send data")
    while True:
        data = str(datetime.datetime.now())
        print('put:', data)

        # add data to queue
        data_queue.put(data)

        await asyncio.sleep(2)

async def main():
    print("read data")
    while True:
        # read queued data from serial port
        if not data_queue.empty():
            data = data_queue.get()
            print('get:', data)

        await asyncio.sleep(1) 

async def start():
    print("start")
    #await send_data()  # doesn't work
    #await read_data()  # doesn't work

    # I had to create all tasks before running
    task1 = asyncio.create_task(send_data())
    task2 = asyncio.create_task(read_data())

    # running task
    await task1
    await task2

asyncio.run(start())

But simpler method is to use asyncio.gather()

async def start():
    print("start")
    await asyncio.gather(
        send_data(),
        read_data(),
    )

Rest is the same as in my previous code

import queue
import asyncio
import datetime

data_queue = queue.Queue()

async def send_data():
    print("send data")
    while True:
        data = str(datetime.datetime.now())
        print('put:', data)

        # add data to queue
        data_queue.put(data)

        await asyncio.sleep(2)

async def main():
    print("read data")
    while True:
        # read queued data from serial port
        if not data_queue.empty():
            data = data_queue.get()
            print('get:', data)

        await asyncio.sleep(1) 

async def start():
    print("start")
    await asyncio.gather(
        send_data(),
        read_data(),
    )

asyncio.run(start())

Notes:

Stackoverflow serial_asyncio: read serial port into a queue and read that queue from main() not working

BTW: Problem with queue: when there is no data in queue then get() may block code and it is better to check if it is not empty()

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