Issue 4301: incorrect and inconsistent logging in multiprocessing (original) (raw)

Created on 2008-11-11 19:50 by dursobr, last changed 2022-04-11 14:56 by admin. This issue is now closed.

Messages (5)

msg75757 - (view)

Author: Brian D'Urso (dursobr)

Date: 2008-11-11 19:50

logging in multiprocessing seems to give inconsistent results on Linux and XP, but neither appears to match the documentation:

According to the docs, when first created "the logger has level logging.NOTSET and has a handler which sends output to sys.stderr using format '[%(levelname)s/%(processName)s] %(message)s'" The example in the docs also does not work, but the full problem is more clearly illustrated with the following:

This should print a message from the main process and the subprocess:

import multiprocessing, logging

def f(): logger = multiprocessing.get_logger() logger.info('info from subprocess')

if name == 'main': logger = multiprocessing.get_logger() logger.setLevel(logging.INFO) logger.info('info from main process') p = multiprocessing.Process(target=f) p.start() p.join()

but, on Windows (XP) and Linux (ScientificLinux 5.2, python 2.6 compiled from src) it outputs only:

No handlers could be found for logger "multiprocessing"

We can 'fix' this by specifying a handler, as in:

import multiprocessing, logging

def f(): logger = multiprocessing.get_logger() logger.info('info from subprocess')

if name == 'main': logger = multiprocessing.get_logger() logger.setLevel(logging.INFO) handler = logging.StreamHandler() handler.setLevel(logging.INFO) formatter = logging.Formatter('[%(levelname)s/%(processName)s] %(message)s') handler.setFormatter(formatter) logger.addHandler(handler) logger.info('info from main process') p = multiprocessing.Process(target=f) p.start() p.join()

Then on Linux I get:

[INFO/MainProcess] info from main process [INFO/Process-1] child process calling self.run() [INFO/Process-1] info from subprocess [INFO/Process-1] process shutting down [INFO/Process-1] process exiting with exitcode 0 [INFO/MainProcess] process shutting down

which looks better, but on Windows I get:

[INFO/MainProcess] info from main process No handlers could be found for logger "multiprocessing" [INFO/MainProcess] process shutting down

So, the logger is still not setup correctly in the subprocess on Windows. We can again try to 'fix' this to:

import multiprocessing, logging

def f(): logger = multiprocessing.get_logger() handler = logging.StreamHandler() handler.setLevel(logging.INFO) formatter = logging.Formatter('[%(levelname)s/%(processName)s] %(message)s') handler.setFormatter(formatter) logger.addHandler(handler) logger.info('info from subprocess')

Now, on Linux I get:

[INFO/MainProcess] info from main process [INFO/Process-1] child process calling self.run() [INFO/Process-1] info from subprocess [INFO/Process-1] info from subprocess [INFO/Process-1] process shutting down [INFO/Process-1] process shutting down [INFO/Process-1] process exiting with exitcode 0 [INFO/Process-1] process exiting with exitcode 0 [INFO/MainProcess] process shutting down

i.e. double output from the subprocess! On Windows, I finally get:

[INFO/MainProcess] info from main process No handlers could be found for logger "multiprocessing" [INFO/Process-1] info from subprocess [INFO/Process-1] process shutting down [INFO/Process-1] process exiting with exitcode 0 [INFO/MainProcess] process shutting down

which is almost OK, but the logger is getting set up too late to pick up the subprocess self.run

It seems like the logger is not being setup correctly by multiprocessing.get_logger() and the behavior is different in a subprocess on Windows vs Linux.

msg79206 - (view)

Author: Gregor Kopka (Gregor_Kopka)

Date: 2009-01-05 22:51

I ran into this shortly but was able to overcome it by patching /Lib/logging/init.py:

43-44: import threading

import multiprocessing

except ImportError:

270-271: self.process = os.getpid()

       self.processName = multiprocessing.current_process()._name
   else:

(and some info about %(processName)s into the docstring) to make it usable for me.

After that the following works like intended:

import multiprocessing import logging logging.basicConfig(level=logging.DEBUG, format='%(asctime)s %(processName)s %(threadName)s %(levelname)s %(message)s')

omit next line to get only what your code is logging

logger = multiprocessing.get_logger()

def f(): logging.info('info from subprocess')

if name == 'main': logging.info('info from main process') p = multiprocessing.Process(target=f) p.start() p.join()

Surely no perfect solution, but the monkey-patching in multiprocessing.util._check_logger_class() dosn't seem to do the trick.

Other option is to not use %(processName)s in logging format, but %(process)s instead - then it works without patching the logging module (but you get numeric process IDs):

import multiprocessing

import logging logging.basicConfig(level=logging.DEBUG, format='%(asctime)s %(process)s %(threadName)s %(levelname)s %(message)s')

omit next line to get only what your code is logging

logger = multiprocessing.get_logger()

def f(): logging.info('info from subprocess')

if name == 'main': logging.info('info from main process') p = multiprocessing.Process(target=f) p.start() p.join()

2009-01-05 23:48:02,046 4000 MainThread INFO info from main process 2009-01-05 23:48:02,187 3968 MainThread INFO child process calling self.run() 2009-01-05 23:48:02,187 3968 MainThread INFO info from subprocess 2009-01-05 23:48:02,187 3968 MainThread INFO process shutting down 2009-01-05 23:48:02,187 3968 MainThread DEBUG running all "atexit" finalizers with priority >= 0 2009-01-05 23:48:02,187 3968 MainThread DEBUG running the remaining "atexit" finalizers 2009-01-05 23:48:02,203 3968 MainThread INFO process exiting with exitcode 0 2009-01-05 23:48:02,203 4000 Dummy-1 INFO process shutting down 2009-01-05 23:48:02,203 4000 Dummy-1 DEBUG running all "atexit" finalizers with priority >= 0 2009-01-05 23:48:02,203 4000 Dummy-1 DEBUG running the remaining "atexit" finalizers

msg80122 - (view)

Author: Jesse Noller (jnoller) * (Python committer)

Date: 2009-01-18 20:36

This is a patch to fix the logging module, and remove the crufty code in multiprocessing.

msg80124 - (view)

Author: Jesse Noller (jnoller) * (Python committer)

Date: 2009-01-18 20:48

remove the import, not needed. switch to the property

msg80127 - (view)

Author: Jesse Noller (jnoller) * (Python committer)

Date: 2009-01-18 21:13

fixed in r68737, merged to py3k in 68740

History

Date

User

Action

Args

2022-04-11 14:56:41

admin

set

github: 48551

2009-01-18 21:13:15

jnoller

set

status: open -> closed
resolution: fixed
messages: +

2009-01-18 20:54:51

jnoller

set

files: - issue4301.patch

2009-01-18 20:48:07

jnoller

set

files: + issue4301.patch
messages: +

2009-01-18 20:47:47

jnoller

set

messages: -

2009-01-18 20:44:57

jnoller

set

files: + issue4301.patch
messages: +

2009-01-18 20:44:31

jnoller

set

files: - issue4301.patch

2009-01-18 20:36:43

jnoller

set

keywords: + needs review, patch
files: + issue4301.patch
messages: +

2009-01-05 22:51:25

Gregor_Kopka

set

nosy: + Gregor_Kopka
messages: +

2008-11-11 21:54:16

benjamin.peterson

set

assignee: jnoller
nosy: + jnoller

2008-11-11 19:50:53

dursobr

create