Launching parallel tasks: Subprocess output triggers function asynchronously - python-3.x

Question

The example I will describe here is purely conceptual so I'm not interested in solving this actual problem.
What I need to accomplish is to be able to asynchronously run a function based on a continuous output of a subprocess command, in this case, the windows ping yahoo.com -t command and based on the time value from the replies I want to trigger the startme function. Now inside this function, there will be some more processing done, including some database and/or network-related calls so basically I/O processing.
My best bet would be that I should use Threading but for some reason, I can't get this to work as intended. Here is what I have tried so far:
First of all I tried the old way of using Threads like this:
import subprocess
import re
import asyncio
import time
import threading
def startme(mytime: int):
print(f"Mytime {mytime} was started!")
time.sleep(mytime) ## including more long operation functions here such as database calls and even some time.sleep() - if possible
print(f"Mytime {mytime} finished!")
myproc = subprocess.Popen(['ping', 'yahoo.com', '-t'], shell=True, stdout=subprocess.PIPE)
def main():
while True:
output = myproc.stdout.readline()
if myproc.poll() is not None:
break
myoutput = output.strip().decode(encoding="UTF-8")
print(myoutput)
mytime = re.findall("(?<=time\=)(.*)(?=ms\s)", myoutput)
try:
mytime = int(mytime[0])
if mytime < 197:
# startme(int(mytime[0]))
p1 = threading.Thread(target=startme(mytime), daemon=True)
# p1 = threading.Thread(target=startme(mytime)) # tried with and without the daemon
p1.start()
# p1.join()
except:
pass
main()
But right after startme() fire for the first time, the pings stop showing and they are waiting for the startme.time.sleep() to finish.
I did manage to get this working using the concurrent.futures's ThreadPoolExecutor but when tried to replace the time.sleep() with the actual database query I found out that my startme() function will never complete so no Mytime xxx finished! message is ever shown nor any database entry is being made.
import sqlite3
import subprocess
import re
import asyncio
import time
# import threading
# import multiprocessing
from concurrent.futures import ThreadPoolExecutor
from concurrent.futures import ProcessPoolExecutor
conn = sqlite3.connect('test.db')
c = conn.cursor()
c.execute(
'''CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY, u1, u2, u3, u4)''')
def startme(mytime: int):
print(f"Mytime {mytime} was started!")
# time.sleep(mytime) ## including more long operation functions here such as database calls and even some time.sleep() - if possible
c.execute("INSERT INTO mytable VALUES (null, ?, ?, ?, ?)",(1,2,3,mytime))
conn.commit()
print(f"Mytime {mytime} finished!")
myproc = subprocess.Popen(['ping', 'yahoo.com', '-t'], shell=True, stdout=subprocess.PIPE)
def main():
while True:
output = myproc.stdout.readline()
myoutput = output.strip().decode(encoding="UTF-8")
print(myoutput)
mytime = re.findall("(?<=time\=)(.*)(?=ms\s)", myoutput)
try:
mytime = int(mytime[0])
if mytime < 197:
print(f"The time {mytime} is low enought to call startme()" )
executor = ThreadPoolExecutor()
# executor = ProcessPoolExecutor() # I did tried using process even if it's not a CPU-related issue
executor.submit(startme, mytime)
except:
pass
main()
I did try using asyncio but I soon realized this is not the case but I'm wondering if I should try aiosqlite
I also thought about using asyncio.create_subprocess_shell and run both as parallel subprocesses but can't think of a way to wait for a certain string from the ping command that would trigger the second script.
Please note that I don't really need a return from the startme() function and the ping command example is conceptually derived from the mitmproxy's mitmdump output command.

Answer 1

The first code wasn't working as I did a stupid mistake when creating the thread so p1 = threading.Thread(target=startme(mytime)) does not take the function with its arguments but separately like this p1 = threading.Thread(target=startme, args=(mytime,))
The reason why I could not get the SQL insert statement to work in my second code was this error:
SQLite objects created in a thread can only be used in that same thread. The object was created in thread id 10688 and this is thread id 17964
that I didn't saw until I wrapped my SQL statement into a try/except and captured the error. So I needed to make the SQL database connection inside my startme() function
The other asyncio stuff was just nonsense and cannot be applied to the current issue here.