New submission from Volodymyr Orlenko <orle...@gmail.com>:
I think I've found a small bug with multiprocessing package on
Windows. If you try to start a multiprocessing.Process from a Python-
based Windows service, the child process will fail to run. When
running the parent process as a regular Python program, everything
works as expected.
I've tracked the problem down to how main_path is prepared in
multiprocessing.forking.get_preparation_data() (lines 370-377):
def get_preparation_data(name):
[...skipped a few lines...]
if not WINEXE:
main_path = getattr(sys.modules['__main__'], '__file__', None)
if not main_path and sys.argv[0] not in ('', '-c'):
main_path = sys.argv[0]
if main_path is not None:
if not os.path.isabs(main_path) and \
process.ORIGINAL_DIR is not
None:
main_path = os.path.join(process.ORIGINAL_DIR,
main_path)
d['main_path'] = os.path.normpath(main_path)
return d
When the program is running as a Windows service, but is not packaged
into a single executable, main_path will become the path to the
service executable (typically, pythonservice.exe). When this data
makes it to the child process, the prepare() function will treat
main_path as a path to a python module, and will try to import it.
This causes it to fail.
My quick-and-dirty solution was to check in get_preparation_data() if
main_path ends with '.exe', and if it does, to not pass it at all.
This solves the problem in my case, but perhaps there's a better way
to fix this? Here is my version of get_preparation_data():
def get_preparation_data(name):
'''
Return info about parent needed by child to unpickle process
object
'''
from .util import _logger, _log_to_stderr
d = dict(
name=name,
sys_path=sys.path,
sys_argv=sys.argv,
log_to_stderr=_log_to_stderr,
orig_dir=process.ORIGINAL_DIR,
authkey=process.current_process().authkey,
)
if _logger is not None:
d['log_level'] = _logger.getEffectiveLevel()
if not WINEXE:
main_path = getattr(sys.modules['__main__'], '__file__', None)
if not main_path and sys.argv[0] not in ('', '-c'):
main_path = sys.argv[0]
if main_path is not None:
if not os.path.isabs(main_path) and \
process.ORIGINAL_DIR is not
None:
main_path = os.path.join(process.ORIGINAL_DIR,
main_path)
if not main_path.endswith('.exe'):
d['main_path'] = os.path.normpath(main_path)
return d
----------
components: Library (Lib)
files: forking-patch
messages: 81247
nosy: jnoller, orlenko
severity: normal
status: open
title: multiprocessing cannot spawn child from a Windows service
type: behavior
versions: Python 2.6
Added file: http://bugs.python.org/file12949/forking-patch
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue5162>
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