我一直在试验多处理,并遇到守护进程的思维障碍。
我有一个守护进程和一个非守护进程,守护进程无限期地每隔一秒发出一次输出,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出现。
回顾过去关于守护进程的 SO 问题,常见问题似乎是其他进程在守护进程之前结束,或者标准输出需要刷新以显示输出。两者(我认为)都已得到解决,但我仍然只看到来自非守护进程的打印输出。
代码:
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()
预期输出:
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
实际产生了什么:
Process-2 starting...
Process-2 ending...
任何关于为什么会发生这种情况的建议将不胜感激。
最佳答案
您可以通过放置
打开日志记录来更清楚地了解事件的顺序import multiprocessing as mp
logger = mp.log_to_stderr(logging.INFO)
在其他导入语句之后。然后你的程序会产生类似的东西:
[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,main 首先开始关闭,然后终止守护进程 Process-1。这就是为什么在 Process-2 继续时您不会再看到任何哔哔声的原因。
关于python - 为什么 Python 多处理守护进程不打印到标准输出?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/27720281/