[英]Why is a Python multiprocessing daemon process not printing to standard output?
我一直在尝试多处理,并使用守护进程运行到一个mindblock。
我有一个守护进程和一个非守护进程,守护进程每隔一秒无限期地发出输出,而非守护进程在启动时立即打印输出,休眠3秒,然后再次打印并返回。
问题是,守护进程的预期输出根本没有显示出来。
回顾过去关于守护进程的SO问题,常见问题似乎是在守护进程之前结束的其他进程,或者需要刷新以显示输出的stdout。 两者都(我认为 )已得到解决,但我仍然只看到来自非守护进程的打印输出。
编码:
from multiprocessing import Process, current_process
import sys
import time
def worker():
"""
Announce that the process has started, sleep 3 seconds
then announce that the process is ending.
"""
name = current_process().name
print name, 'starting...'
sys.stdout.flush()
time.sleep(3)
print name, 'ending...'
sys.stdout.flush()
return
def daemon():
"""
Announce that the process has started, beep, then beep
once every second
"""
name = current_process().name
print name, 'starting...'
print 'beep...'
sys.stdout.flush()
while True:
time.sleep(1)
print 'beep...'
sys.stdout.flush()
if __name__=='__main__':
d = Process(target=daemon)
d.daemon = True
d.start()
p = Process(target=worker)
p.daemon = False
p.start()
预期产出:
Process-1 starting... # Order here may vary
beep...
Process-2 starting...
beep...
beep...
Process-2 ending... #There may or may not be another beep here
实际生产的内容:
Process-2 starting...
Process-2 ending...
任何关于为什么会发生这种情况的建议都会得到真正的体会
您可以通过放置打开日志来更清楚地了解事件的顺序
import multiprocessing as mp
logger = mp.log_to_stderr(logging.INFO)
在其他进口声明之后。 然后你的程序将产生类似于:
[INFO/Process-1] child process calling self.run()
[INFO/MainProcess] process shutting down
Process-1 starting...
beep...
[INFO/Process-2] child process calling self.run()
[INFO/MainProcess] calling terminate() for daemon Process-1
Process-2 starting...
[INFO/MainProcess] calling join() for process Process-2
Process-2 ending...
[INFO/Process-2] process shutting down
[INFO/Process-2] process exiting with exitcode 0
[INFO/MainProcess] calling join() for process Process-1
因此,主要开始先关闭,然后终止进程-1,即守护进程。 这就是为什么在Process-2继续时你不会再看到哔哔声的原因。
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