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# Code used to start processes when using the spawn or forkserver

# start methods.

# multiprocessing/spawn.py

# Licensed to PSF under a Contributor Agreement.

import os

import sys

import runpy

import types

from . import get_start_method, set_start_method

from . import process

from .context import reduction

from . import util

__all__ = ['_main', 'freeze_support', 'set_executable', 'get_executable',

'get_preparation_data', 'get_command_line', 'import_main_path']

# _python_exe is the assumed path to the python executable.

# People embedding Python want to modify it.

if sys.platform != 'win32':

WINEXE = False

WINSERVICE = False

else:

WINEXE = getattr(sys, 'frozen', False)

WINSERVICE = sys.executable and sys.executable.lower().endswith("pythonservice.exe")

def set_executable(exe):

global _python_exe

if exe is None:

_python_exe = exe

elif sys.platform == 'win32':

_python_exe = os.fsdecode(exe)

else:

_python_exe = os.fsencode(exe)

def get_executable():

return _python_exe

if WINSERVICE:

set_executable(os.path.join(sys.exec_prefix, 'python.exe'))

else:

set_executable(sys.executable)

def is_forking(argv):

'''

Return whether commandline indicates we are forking

'''

if len(argv) >= 2 and argv[1] == '--multiprocessing-fork':

return True

else:

return False

def freeze_support():

'''

Run code for process object if this in not the main process

'''

if is_forking(sys.argv):

kwds = {}

for arg in sys.argv[2:]:

name, value = arg.split('=')

if value == 'None':

kwds[name] = None

else:

kwds[name] = int(value)

spawn_main(**kwds)

sys.exit()

def get_command_line(**kwds):

'''

Returns prefix of command line used for spawning a child process

'''

if getattr(sys, 'frozen', False):

return ([sys.executable, '--multiprocessing-fork'] +

['%s=%r' % item for item in kwds.items()])

else:

prog = 'from multiprocessing.spawn import spawn_main; spawn_main(%s)'

prog %= ', '.join('%s=%r' % item for item in kwds.items())

opts = util._args_from_interpreter_flags()

exe = get_executable()

return [exe] + opts + ['-c', prog, '--multiprocessing-fork']

def spawn_main(pipe_handle, parent_pid=None, tracker_fd=None):

'''

Run code specified by data received over pipe

'''

assert is_forking(sys.argv), "Not forking"

if sys.platform == 'win32':

import msvcrt

import _winapi

if parent_pid is not None:

source_process = _winapi.OpenProcess(

_winapi.SYNCHRONIZE | _winapi.PROCESS_DUP_HANDLE,

False, parent_pid)

else:

source_process = None

new_handle = reduction.duplicate(pipe_handle,

source_process=source_process)

fd = msvcrt.open_osfhandle(new_handle, os.O_RDONLY)

parent_sentinel = source_process

else:

from . import resource_tracker

resource_tracker._resource_tracker._fd = tracker_fd

fd = pipe_handle

parent_sentinel = os.dup(pipe_handle)

exitcode = _main(fd, parent_sentinel)

sys.exit(exitcode)

def _main(fd, parent_sentinel):

with os.fdopen(fd, 'rb', closefd=True) as from_parent:

process.current_process()._inheriting = True

try:

preparation_data = reduction.pickle.load(from_parent)

prepare(preparation_data)

self = reduction.pickle.load(from_parent)

finally:

del process.current_process()._inheriting

return self._bootstrap(parent_sentinel)

def _check_not_importing_main():

if getattr(process.current_process(), '_inheriting', False):

raise RuntimeError('''

An attempt has been made to start a new process before the

current process has finished its bootstrapping phase.

This probably means that you are not using fork to start your

child processes and you have forgotten to use the proper idiom

in the main module:

if __name__ == '__main__':

freeze_support()

...

The "freeze_support()" line can be omitted if the program

is not going to be frozen to produce an executable.

To fix this issue, refer to the "Safe importing of main module"

section in https://docs.python.org/3/library/multiprocessing.html

''')

def get_preparation_data(name):

'''

Return info about parent needed by child to unpickle process object

'''

_check_not_importing_main()

d = dict(

log_to_stderr=util._log_to_stderr,

authkey=process.current_process().authkey,

)

if util._logger is not None:

d['log_level'] = util._logger.getEffectiveLevel()

sys_path=sys.path.copy()

try:

i = sys_path.index('')

except ValueError:

pass

else:

sys_path[i] = process.ORIGINAL_DIR

d.update(

name=name,

sys_path=sys_path,

sys_argv=sys.argv,

orig_dir=process.ORIGINAL_DIR,

dir=os.getcwd(),

start_method=get_start_method(allow_none=True),

)

# Figure out whether to initialise main in the subprocess as a module

# or through direct execution (or to leave it alone entirely)

main_module = sys.modules['__main__']

main_mod_name = getattr(main_module.__spec__, "name", None)

if main_mod_name is not None:

d['init_main_from_name'] = main_mod_name

elif sys.platform != 'win32' or (not WINEXE and not WINSERVICE):

main_path = getattr(main_module, '__file__', None)

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['init_main_from_path'] = os.path.normpath(main_path)

return d

# Prepare current process

old_main_modules = []

def prepare(data):

'''

Try to get current process ready to unpickle process object

'''

if 'name' in data:

process.current_process().name = data['name']

if 'authkey' in data:

process.current_process().authkey = data['authkey']

if 'log_to_stderr' in data and data['log_to_stderr']:

util.log_to_stderr()

if 'log_level' in data:

util.get_logger().setLevel(data['log_level'])

if 'sys_path' in data:

sys.path = data['sys_path']

if 'sys_argv' in data:

sys.argv = data['sys_argv']

if 'dir' in data:

os.chdir(data['dir'])

if 'orig_dir' in data:

process.ORIGINAL_DIR = data['orig_dir']

if 'start_method' in data:

set_start_method(data['start_method'], force=True)

if 'init_main_from_name' in data:

_fixup_main_from_name(data['init_main_from_name'])

elif 'init_main_from_path' in data:

_fixup_main_from_path(data['init_main_from_path'])

# Multiprocessing module helpers to fix up the main module in

# spawned subprocesses

def _fixup_main_from_name(mod_name):

# __main__.py files for packages, directories, zip archives, etc, run

# their "main only" code unconditionally, so we don't even try to

# populate anything in __main__, nor do we make any changes to

# __main__ attributes

current_main = sys.modules['__main__']

if mod_name == "__main__" or mod_name.endswith(".__main__"):

return

# If this process was forked, __main__ may already be populated

if getattr(current_main.__spec__, "name", None) == mod_name:

return

# Otherwise, __main__ may contain some non-main code where we need to

# support unpickling it properly. We rerun it as __mp_main__ and make

# the normal __main__ an alias to that

old_main_modules.append(current_main)

main_module = types.ModuleType("__mp_main__")

main_content = runpy.run_module(mod_name,

run_name="__mp_main__",

alter_sys=True)

main_module.__dict__.update(main_content)

sys.modules['__main__'] = sys.modules['__mp_main__'] = main_module

def _fixup_main_from_path(main_path):

# If this process was forked, __main__ may already be populated

current_main = sys.modules['__main__']

# Unfortunately, the main ipython launch script historically had no

# "if __name__ == '__main__'" guard, so we work around that

# by treating it like a __main__.py file

# See https://github.com/ipython/ipython/issues/4698

main_name = os.path.splitext(os.path.basename(main_path))[0]

if main_name == 'ipython':

return

# Otherwise, if __file__ already has the setting we expect,

# there's nothing more to do

if getattr(current_main, '__file__', None) == main_path:

return

# If the parent process has sent a path through rather than a module

# name we assume it is an executable script that may contain

# non-main code that needs to be executed

old_main_modules.append(current_main)

main_module = types.ModuleType("__mp_main__")

main_content = runpy.run_path(main_path,

run_name="__mp_main__")

main_module.__dict__.update(main_content)

sys.modules['__main__'] = sys.modules['__mp_main__'] = main_module

def import_main_path(main_path):

'''

Set sys.modules['__main__'] to module at main_path

'''

_fixup_main_from_path(main_path)

cpython/Lib/multiprocessing/spawn.py at main · python/cpython · GitHub

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