python communicate()在进程terminate()之后挂起

Question

下面的代码尝试并行运行多个命令，每个命令都有一个超时。如果处理在超时之前没有完成，它将被停止(我使用terminate())。

问题是在终止(返回码设置为-ve)后，communicate()方法挂起，当强制退出(Ctrl+C)时，则显示以下错误。

(stdout, stderr) = proc.communicate()
File "python3.7/subprocess.py", line 926, in communicate
stdout = self.stdout.read()

代码

procList = []
for app in appList:
    try:
        p = subprocess.Popen(app['command'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True)
        procList.append((app, p))
    except Exception as e:
        print(e)

start = time.time()
while len(procList):
    time.sleep(30)
    try:
        for app, proc in procList:
            if (time.time() - start > app['timeoutSec']):
                proc.terminate()
            if proc.poll() is not None and app['mailSent'] == 0:
                (stdout, stderr) = proc.communicate() #Hangs here is the process is terminated
                send_results_mail('Execution Completed or Terminated')
                app['mailSent'] = 1
    except subprocess.SubprocessError as e:
        print(e)
    procList = [(app, proc) for (app, proc) in procList if app['mailSent'] == 0]

Answer 1

编辑:这是一个使用kill()的工作示例，它有一个行为不端的子进程(不会响应terminate())，但我不确定你的子进程的性质。希望这篇文章能帮助你更好地解决问题！

简单的子程序，Python 3：

import signal
import time

def sighandler(signal, _stack):
    print(f"Ignoring signal {signal}")

signal.signal(signal.SIGTERM, sighandler)
signal.signal(signal.SIGINT, sighandler)

secs = 10
print(f"Sleeping {secs} seconds...")
time.sleep(secs)
print("Exiting...")

修改的父程序，Python 3：

import subprocess
import time

start = time.time()
appList = [
   {'command': 'python ./child.py', 'timeoutSec': 2, 'mailSent': 0},
   {'command': 'python ./child.py', 'timeoutSec': 2, 'mailSent': 0},
   {'command': 'python ./child.py', 'timeoutSec': 2, 'mailSent': 0},
]

def logmsg(msg):
    elap = time.time()-start
    print(f"{elap:2.1f} secs: {msg}")

def send_results_mail(result):
    logmsg(f"Result: {result}")

procList = []
for app in appList:
    try:
        p = subprocess.Popen(app['command'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT, shell=True)
        procList.append((app, p))
    except Exception as e:
        logmsg(e)
    logmsg(f"Launching child... {p.pid}")

start = time.time()
while len(procList):
    time.sleep(1)
    try:
        for app, proc in procList:
            if (time.time() - start > app['timeoutSec']):
                logmsg(f"Trying to terminate()...{proc.pid}")
                proc.terminate()
                proc.kill()
            if proc.poll() is not None and app['mailSent'] == 0:
                proc.kill()
                logmsg(f"Trying to communicate()...{proc.pid}")
                (stdout, stderr) = proc.communicate()
                send_results_mail('Execution Completed or Terminated')
                app['mailSent'] = 1
    except subprocess.SubprocessError as e:
        logmsg(e)
    procList = [(app, proc) for (app, proc) in procList if app['mailSent'] == 0]

输出：

$ python parent.py
0.0 secs: Launching child... 537567
0.0 secs: Launching child... 537568
0.0 secs: Launching child... 537569
2.0 secs: Trying to terminate()...537567
2.0 secs: Trying to terminate()...537568
2.0 secs: Trying to terminate()...537569
3.0 secs: Trying to terminate()...537567
3.0 secs: Trying to communicate()...537567
3.0 secs: Result: Execution Completed or Terminated
3.0 secs: Trying to terminate()...537568
3.0 secs: Trying to communicate()...537568
3.0 secs: Result: Execution Completed or Terminated
3.0 secs: Trying to terminate()...537569
3.0 secs: Trying to communicate()...537569
3.0 secs: Result: Execution Completed or Terminated

Answer 2

感谢所有的建议和回应，但没有什么能解决问题，因为对我来说，我所跨越的流程正在创建多层子流程。

因此，我必须递归地终止进程，为此我使用了使用psutil的解决方案

详情请看下面的帖子

https://stackoverflow.com/a/27034438/2393961

一旦所有子进程和子进程都被终止，communicate()就能正常工作。

我学到的另一点是，即使htop可以向你展示进程的树形结构，但每个进程都是独立的，杀死父进程并不会自动杀死它的后代。感谢我的朋友Noga指出这一点