I am using subprocess.Popen class with threads but it is not working for me

Question content

I have the following files:

ping.py：

from utilities.env import packet_cout, ping_time, max_workers_count
from utilities.cmds import create_ping_cmd
from subprocess import popen, pipe, devnull, timeoutexpired
from re import findall
from concurrent.futures import threadpoolexecutor


max_ping_time = float(packet_cout) * (float(ping_time))
ping_cmd = create_ping_cmd()

def check_ping_process(ping_process):
    ping_result = {}
    try:
        out = ping_process.communicate(timeout=max_ping_time)[0]
        is_successes = findall("ttl", out)
        if ping_process.returncode == 0 and is_successes:
            return true
        else:
            return false
    except timeoutexpired:
        ping_process.kill()
        return false


def ping_ip(ip):
    ping_cmd.append(ip)
    ping_process = popen(
        ping_cmd,
        stdout=pipe,
        stderr=devnull,
        text=true
    )
    result = check_ping_process(ping_process)
    return result


def ping_ip_list(ip_list):
    ping_results = []
    with threadpoolexecutor(max_workers=max_workers_count) as executor:
        results = executor.map(ping_ip, ip_list)
        for ip, result in zip(ip_list, results):
            print({ip, result})
            ping_results.append({ip, result})
    return ping_results

main.py：

from ping import ping_ip_list


ip_list = [
    '192.168.0.100',
    '192.168.0.1',
    '192.168.0.104',
    '192.168.0.124',
    '192.168.0.103'
]
def monitor_network_devices(ip_list):
    results = ping_ip_list(ip_list)

monitor_network_devices(ip_list)

The goal of this program is to find out if a network device is pingable. I am running the main.py file and it is giving wrong results. I tried debugging and it seems to be a thread problem, but I can't solve it.

Any help would be appreciated

Correct answer

Some observations

• As mentioned before, as you keep appending more content to ping_cmd, your command will have more and more ip addresses. It's better to build a new command each time instead of appending to the ping_cmd list

• Consider this line

  is_successes = findall("ttl", out)

  I look at the linux output and it looks like this:

  ping 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
    64 bytes from 192.168.1.1: icmp_seq=1 ttl=63 time=11.9 ms
    64 bytes from 192.168.1.1: icmp_seq=2 ttl=63 time=5.18 ms
  
    --- 192.168.1.1 ping statistics ---
    2 packets transmitted, 2 received, 0% packet loss, time 1024ms
    rtt min/avg/max/mdev = 5.182/8.541/11.901/3.359 ms

  In your code, you search for ttl (uppercase), which will always result in false. Also, to search text you don't need to use regular expressions:

  is_success = "ttl" in out

• Since you didn't post the contents of the utilities package, I don't know what the packet_cout equivalent value is

• When dealing with multi-threading, it is better to use logging instead of print, because the former is thread-safe, while the latter is not.

In this way, this is my proposed solution

# ping.py
import logging
import subprocess
from concurrent.futures import ThreadPoolExecutor

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s | %(levelname)s | %(threadName)-15s | %(funcName)-18s | %(message)s",
)


def ping_ip(ip):
    ping_command = ["ping", "-c1", ip]
    logging.debug("Execute command %r", ping_command)
    completed_process = subprocess.run(
        ping_command,
        text=True,
        capture_output=True,
        check=False,
    )
    success = completed_process.returncode == 0
    logging.debug("%s -> %r", ip, success)
    return success


def ping_ip_list(ip_list):
    with ThreadPoolExecutor() as executor:
        out = dict(zip(ip_list, executor.map(ping_ip, ip_list)))
    return out

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