检查子进程是否正在执行

Question

I am trying to use subprocess.popen to execute another python script that creates a listening socket. I want to pass it a default number for the port to bind on. I also want to catch if the port is already in use and the bind fails. If it fails then I want to call subprocess.popen again and pass it another number to try and bind to.

first.py

import subprocess

p = subprocess.Popen(["python3.7", "test.py", "4444"], shell=False)

#If p is success (bind succeeded) then I want to continue processing code. 
#Else I want to increment the port and try again.

start.py

import socket, sys

HOST = '127.0.0.1'  # Standard loopback interface address (localhost)
PORT = int(sys.argv[1])        # Port to listen on (non-privileged ports are > 1023)

def stuff():
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        try:
            s.bind((HOST, PORT))
        except:
            print("failed to bind")
            return 1
        s.listen()
        print("Listening")
        conn, addr = s.accept()

        with conn:
            print('Connected by', addr)
            while True:
                data = conn.recv(1024)
                if not data:
                    break
                conn.sendall(data)

stuff()

Answer 1

A couple of things:

• Just returning 1 from a function called won't make your process's exit code 1 . Either do sys.exit(stuff()) or just call sys.exit(1) in stuff() .

• You can wait for a subprocess to succeed or fail with p.wait() , after which you can look at p.returncode .

In your case, you'll probably want to do something like

import subprocess

p = subprocess.Popen(["python3.7", "test.py", "4444"], shell=False)
try:
    p.wait(2)
except subprocess.TimeoutExpired:
    pass  # it was probably successful and is now listening
else:
    if p.returncode == 1:
        pass  # nope

And, of course, you could do this with just threads instead of subprocesses.