停止读取Python中没有挂起的进程输出？

停止读取Python中没有挂起的进程输出？

#!/usr/bin/env python"""Start process; wait 2 seconds; kill the process; print all process output."""import subprocessimport tempfileimport timedef main():    # open temporary file (it automatically deleted when it is closed)    #  `Popen` requires `f.fileno()` so `SpooledTemporaryFile` adds nothing here    f = tempfile.TemporaryFile()     # start process, redirect stdout    p = subprocess.Popen(["top"], stdout=f)    # wait 2 seconds    time.sleep(2)    # kill process    #NOTE: if it doesn't kill the process then `p.wait()` blocks forever    p.terminate()     p.wait() # wait for the process to terminate otherwise the output is garbled    # print saved output    f.seek(0) # rewind to the beginning of the file    print f.read(),     f.close()if __name__=="__main__":    main()

类似于尾巴的解决方案，仅打印输出的一部分
你可以在另一个线程中读取过程输出，并将所需数量的最后几行保存在队列中：

import collectionsimport subprocessimport timeimport threadingdef read_output(process, append):    for line in iter(process.stdout.readline, ""):        append(line)def main():    # start process, redirect stdout    process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True)    try:        # save last `number_of_lines` lines of the process output        number_of_lines = 200        q = collections.deque(maxlen=number_of_lines) # atomic .append()        t = threading.Thread(target=read_output, args=(process, q.append))        t.daemon = True        t.start()        #        time.sleep(2)    finally:        process.terminate() #NOTE: it doesn't ensure the process termination    # print saved lines    print ''.join(q)if __name__=="__main__":    main()

此变体必须

q.append()

是原子 *** 作。否则，输出可能会损坏。

signal.alarm()

解
你可以用来 在指定的超时后

signal.alarm()

调用，

process.terminate()

而不用读入另一个线程。尽管它可能无法与

subprocess

模块很好地交互。基于

@Alex Martelli

的答案：

import collectionsimport signalimport subprocessclass Alarm(Exception):    passdef alarm_handler(signum, frame):    raise Alarmdef main():    # start process, redirect stdout    process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True)    # set signal handler    signal.signal(signal.SIGALRM, alarm_handler)    signal.alarm(2) # produce SIGALRM in 2 seconds    try:        # save last `number_of_lines` lines of the process output        number_of_lines = 200        q = collections.deque(maxlen=number_of_lines)        for line in iter(process.stdout.readline, ""): q.append(line)        signal.alarm(0) # cancel alarm    except Alarm:        process.terminate()    finally:        # print saved lines        print ''.join(q)if __name__=="__main__":    main()

该方法仅适用于

* nix

系统。如果

process.stdout.readline()

不返回，它可能会阻塞。

threading.Timer 解import collectionsimport subprocessimport threadingdef main():    # start process, redirect stdout    process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True)    # terminate process in timeout seconds    timeout = 2 # seconds    timer = threading.Timer(timeout, process.terminate)    timer.start()    # save last `number_of_lines` lines of the process output    number_of_lines = 200    q = collections.deque(process.stdout, maxlen=number_of_lines)    timer.cancel()    # print saved lines    print ''.join(q),if __name__=="__main__":    main()

这种方法在Windows上也应适用。在这里，我用作

process.stdout

迭代。它可能会引入额外的输出缓冲，

iter(process.stdout.readline

, “”)如果不希望的话，你可以切换到该方法。如果进程没有终止，

process.terminate()

则脚本挂起。

没有线程，没有信号解决方案

import collectionsimport subprocessimport sysimport timedef main():    args = sys.argv[1:]    if not args:        args = ['top']    # start process, redirect stdout    process = subprocess.Popen(args, stdout=subprocess.PIPE, close_fds=True)    # save last `number_of_lines` lines of the process output    number_of_lines = 200    q = collections.deque(maxlen=number_of_lines)    timeout = 2 # seconds    now = start = time.time()        while (now - start) < timeout:        line = process.stdout.readline()        if not line: break        q.append(line)        now = time.time()    else: # on timeout        process.terminate()    # print saved lines    print ''.join(q),if __name__=="__main__":    main()

此变型既不使用线程，也不使用信号，但会在终端中产生乱码输出。如果

process.stdout.readline()

阻塞，它将阻塞。