如何在使用join()后杀死执行中间的进程?

Question

我想在某个进程或所有进程的执行过程中杀死它。我的示例代码如下。我该怎么做呢?在这里，我想基于当前时间终止进程。如果时间能被2整除，我希望终止进程，否则不希望。

import time
from multiprocessing import Process

def runTests(a, b):
time.sleep(10)
return a + b

def main(kill_processes):
print(kill_processes)
processes = []
for i in range(3):
print(i)
proc = Process(target=runTests, args=(2, 4,))
processes.append(proc)
proc.start()
for proc in processes:
proc.join()
if kill_processes:
print("killing")
proc.terminate()

if __name__ == "__main__":
if round(time.time()) % 2 == 0:
main(True)
else:
main(False)

Answer 1

这说明了如何通过使用多个线程来实现这一点，其方式类似于我建议您查看的可停止多线程中的多处理问题的答案。

基本上所有的join()调用都是在单独的线程中完成的，所以它们不会阻塞主进程中的主线程——这使得它有可能杀死它们。

import threading
import time
from multiprocessing import Process

def runTests(a, b):
time.sleep(10)
return a + b
def create_process(lock, i):
proc = Process(target=runTests, args=(2, 4,))
print(f'{proc.name} created')
proc.start()
with lock:
processes.append(proc)
proc.join()

def main(kill_processes):
global processes
N = 3
lock = threading.RLock()
processes = []
print(f'main({kill_processes=})')
for i in range(N):
thread = threading.Thread(target=create_process, args=(lock, i))
thread.start()
while True:  # Wait for all processes to have been created.
with lock:
if len(processes) == N:
break
else:
time.sleep(.001)
if kill_processes:
print("Killing the processes")
for proc in processes:
proc.terminate()
print(f'process {proc} terminated')

if __name__ == "__main__":
main(True)
#    if round(time.time()) % 2 == 0:
#        main(True)
#    else:
#        main(False)

Answer 2

可以使用多进程。事件向子进程发出终止条件的信号。不要在主进程中加入子进程。相反，让主进程和子进程在各自的循环中运行。检查主循环中的终止条件，并使用multiprocessing.Event向子进程发出信号。

Event对象作为参数传递给子进程。子进程不断检查是否设置了事件，如果设置了，则停止其工作。主循环检查终止条件，如果条件满足，则设置Event(在下面的示例中，主循环等待Ctrl+c)。

import multiprocessing as mp
import os
import time

def do_work(a, b, stop_event):
while not stop_event.is_set():
try:
time.sleep(2)
print(f"worker {os.getpid()}: working ...", a + b)
a += 1
b += 1
except KeyboardInterrupt:
print(f"worker {os.getpid()}: received SIGINT. ignore.")
pass
print(f"worker {os.getpid()}: stop_event is set. exit.")

if __name__ == "__main__":
stop_event = mp.Event()
procs = []
for i in range(3):
# p = mp.Process(target=do_work, args=(1, 2, stop_event), daemon=True)
p = mp.Process(target=do_work, args=(1, 2, stop_event))
p.start()
procs.append(p)
while True:
try:
print("main: waiting for termination signal")
time.sleep(1)
except KeyboardInterrupt:
print("main: received termination signal")            
stop_event.set()

# wait for the processes to stop
for p in procs:
p.join()
for p in procs:
print(f"worker {p.pid} is terminated: {not p.is_alive()}")

# exit the main loop
break

print("main: bye")

Answer 3

如果需要按时间终止，则使用join的timeout参数。一种方法是设置停止时间，当每个进程加入时，使用剩余时间作为其超时。

import time
from multiprocessing import Process
def runTests(a, b):
time.sleep(10)
return a + b
def main(kill_processes):
print(kill_processes)
processes = []
end = time.time() + 10 # wait 10 seconds
for i in range(3):
print(i)
proc = Process(target=runTests, args=(2, 4,))
processes.append(proc)
proc.start()
for proc in processes:
if kill_processes:
delta = end - time.time()
else:
delta = None
proc.join(delta)
if kill_processes:
print("killing")
proc.terminate()
proc.join(1)
if proc.is_alive():
proc.kill()
if __name__ == "__main__":
if round(time.time()) % 2 == 0:
main(True)
else:
main(False)