Bagaimana untuk Mengelakkan Readline Hang Apabila Menghentikan Output Proses dalam Python?

Mengelakkan Readline Hang Apabila Menghentikan Output Proses dalam Python

Penerangan Masalah:

Dalam atur cara Python menggunakan os.popen () atau subprocess.Popen() untuk membaca output proses pengemaskinian yang berterusan (seperti atas), program mungkin tergantung apabila cuba membaca semua baris menggunakan readlines().

Penyelesaian:

Menggunakan Fail Sementara dan Proses Anak:

<code class="python">import subprocess
import tempfile
import time

def main():
    # Open a temporary file for process output
    with tempfile.TemporaryFile() as f:
        # Start the process and redirect its stdout to the file
        process = subprocess.Popen(["top"], stdout=f)

        # Wait for a specified amount of time
        time.sleep(2)

        # Kill the process
        process.terminate()
        process.wait()  # Wait for the process to terminate to ensure complete output

        # Seek to the beginning of the file and print its contents
        f.seek(0)
        print(f.read())

if __name__ == "__main__":
    main()</code>

Pendekatan ini menggunakan fail sementara untuk menyimpan output proses, membenarkan atur cara mengelak daripada menyekat pada readlines().

Penyelesaian Alternatif:

Menggunakan Baris Gilir dengan Benang Lain:

<code class="python">import collections
import subprocess
import threading

def main():
    # Create a queue to store process output
    q = collections.deque()

    # Start the process and redirect its stdout to a thread
    process = subprocess.Popen(["top"], stdout=subprocess.PIPE)
    t = threading.Thread(target=process.stdout.readline, args=(q.append,))
    t.daemon = True
    t.start()

    # Wait for a specified amount of time
    time.sleep(2)

    # Terminate the process
    process.terminate()
    t.join()  # Wait for the thread to finish

    # Print the stored output
    print(''.join(q))

if __name__ == "__main__":
    main()</code>

Menggunakan signal.alarm():

<code class="python">import collections
import signal
import subprocess

class Alarm(Exception):
    pass

def alarm_handler(signum, frame):
    raise Alarm

def main():
    # Create a queue to store process output
    q = collections.deque()

    # Register a signal handler to handle alarm
    signal.signal(signal.SIGALRM, alarm_handler)

    # Start the process and redirect its stdout
    process = subprocess.Popen(["top"], stdout=subprocess.PIPE)

    # Set an alarm to terminate the process after a specified amount of time
    signal.alarm(2)

    # Read lines until the alarm is raised or the process terminates
    try:
        while True:
            line = process.stdout.readline()
            if not line:
                break
            q.append(line)
    except Alarm:
        process.terminate()

    # Cancel the alarm if it hasn't already fired
    signal.alarm(0)

    # Wait for the process to finish
    process.wait()

    # Print the stored output
    print(''.join(q))

if __name__ == "__main__":
    main()</code>

Alternatif ini membenarkan program untuk terus berjalan sambil menyimpan output proses. Ia mungkin lebih sesuai untuk kes di mana anda perlu memantau output proses secara berterusan.

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