#

# Module providing the `Process` class which emulates `threading.Thread`

#

# multiprocessing/process.py

#

# Copyright (c) 2006-2008, R Oudkerk

# Licensed to PSF under a Contributor Agreement.

#

__all__ = ['BaseProcess', 'current_process', 'active_children',

'parent_process']

#

# Imports

#

import os

import sys

import signal

import itertools

import threading

from _weakrefset import WeakSet

#

#

#

try:

ORIGINAL_DIR = os.path.abspath(os.getcwd())

except OSError:

ORIGINAL_DIR = None

#

# Public functions

#

def current_process():

'''

Return process object representing the current process

'''

return _current_process

def active_children():

'''

Return list of process objects corresponding to live child processes

'''

_cleanup()

return list(_children)

def parent_process():

'''

Return process object representing the parent process

'''

return _parent_process

#

#

#

def _cleanup():

# check for processes which have finished

for p in list(_children):

if (child_popen := p._popen) and child_popen.poll() is not None:

_children.discard(p)

#

# The `Process` class

#

class BaseProcess(object):

'''

Process objects represent activity that is run in a separate process

The class is analogous to `threading.Thread`

'''

def _Popen(self):

raise NotImplementedError

def __init__(self, group=None, target=None, name=None, args=(), kwargs=None,

*, daemon=None):

assert group is None, 'group argument must be None for now'

count = next(_process_counter)

self._identity = _current_process._identity + (count,)

self._config = _current_process._config.copy()

self._parent_pid = os.getpid()

self._parent_name = _current_process.name

self._popen = None

self._closed = False

self._target = target

self._args = tuple(args)

self._kwargs = dict(kwargs) if kwargs else {}

self._name = name or type(self).__name__ + '-' + \

':'.join(str(i) for i in self._identity)

if daemon is not None:

self.daemon = daemon

_dangling.add(self)

def _check_closed(self):

if self._closed:

raise ValueError("process object is closed")

def run(self):

'''

Method to be run in sub-process; can be overridden in sub-class

'''

if self._target:

self._target(*self._args, **self._kwargs)

def start(self):

'''

Start child process

'''

self._check_closed()

assert self._popen is None, 'cannot start a process twice'

assert self._parent_pid == os.getpid(), \

'can only start a process object created by current process'

assert not _current_process._config.get('daemon'), \

'daemonic processes are not allowed to have children'

_cleanup()

self._popen = self._Popen(self)

self._sentinel = self._popen.sentinel

# Avoid a refcycle if the target function holds an indirect

# reference to the process object (see bpo-30775)

del self._target, self._args, self._kwargs

_children.add(self)

def interrupt(self):

'''

Terminate process; sends SIGINT signal

'''

self._check_closed()

self._popen.interrupt()

def terminate(self):

'''

Terminate process; sends SIGTERM signal or uses TerminateProcess()

'''

self._check_closed()

self._popen.terminate()

def kill(self):

'''

Terminate process; sends SIGKILL signal or uses TerminateProcess()

'''

self._check_closed()

self._popen.kill()

def join(self, timeout=None):

'''

Wait until child process terminates

'''

self._check_closed()

assert self._parent_pid == os.getpid(), 'can only join a child process'

assert self._popen is not None, 'can only join a started process'

res = self._popen.wait(timeout)

if res is not None:

_children.discard(self)

def is_alive(self):

'''

Return whether process is alive

'''

self._check_closed()

if self is _current_process:

return True

assert self._parent_pid == os.getpid(), 'can only test a child process'

if self._popen is None:

return False

returncode = self._popen.poll()

if returncode is None:

return True

else:

_children.discard(self)

return False

def close(self):

'''

Close the Process object.

This method releases resources held by the Process object. It is

an error to call this method if the child process is still running.

'''

if self._popen is not None:

if self._popen.poll() is None:

raise ValueError("Cannot close a process while it is still running. "

"You should first call join() or terminate().")

self._popen.close()

self._popen = None

del self._sentinel

_children.discard(self)

self._closed = True

@property

def name(self):

return self._name

@name.setter

def name(self, name):

assert isinstance(name, str), 'name must be a string'

self._name = name

@property

def daemon(self):

'''

Return whether process is a daemon

'''

return self._config.get('daemon', False)

@daemon.setter

def daemon(self, daemonic):

'''

Set whether process is a daemon

'''

assert self._popen is None, 'process has already started'

self._config['daemon'] = daemonic

@property

def authkey(self):

return self._config['authkey']

@authkey.setter

def authkey(self, authkey):

'''

Set authorization key of process

'''

self._config['authkey'] = AuthenticationString(authkey)

@property

def exitcode(self):

'''

Return exit code of process or `None` if it has yet to stop

'''

self._check_closed()

if self._popen is None:

return self._popen

return self._popen.poll()

@property

def ident(self):

'''

Return identifier (PID) of process or `None` if it has yet to start

'''

self._check_closed()

if self is _current_process:

return os.getpid()

else:

return self._popen and self._popen.pid

pid = ident

@property

def sentinel(self):

'''

Return a file descriptor (Unix) or handle (Windows) suitable for

waiting for process termination.

'''

self._check_closed()

try:

return self._sentinel

except AttributeError:

raise ValueError("process not started") from None

def __repr__(self):

exitcode = None

if self is _current_process:

status = 'started'

elif self._closed:

status = 'closed'

elif self._parent_pid != os.getpid():

status = 'unknown'

elif self._popen is None:

status = 'initial'

else:

exitcode = self._popen.poll()

if exitcode is not None:

status = 'stopped'

else:

status = 'started'

info = [type(self).__name__, 'name=%r' % self._name]

if self._popen is not None:

info.append('pid=%s' % self._popen.pid)

info.append('parent=%s' % self._parent_pid)

info.append(status)

if exitcode is not None:

exitcode = _exitcode_to_name.get(exitcode, exitcode)

info.append('exitcode=%s' % exitcode)

if self.daemon:

info.append('daemon')

return '<%s>' % ' '.join(info)

##

def _bootstrap(self, parent_sentinel=None):

from . import util, context

global _current_process, _parent_process, _process_counter, _children

try:

if self._start_method is not None:

context._force_start_method(self._start_method)

_process_counter = itertools.count(1)

_children = set()

util._close_stdin()

old_process = _current_process

_current_process = self

_parent_process = _ParentProcess(

self._parent_name, self._parent_pid, parent_sentinel)

if threading._HAVE_THREAD_NATIVE_ID:

threading.main_thread()._set_native_id()

try:

self._after_fork()

finally:

# delay finalization of the old process object until after

# _run_after_forkers() is executed

del old_process

util.info('child process calling self.run()')

self.run()

exitcode = 0

except SystemExit as e:

if e.code is None:

exitcode = 0

elif isinstance(e.code, int):

exitcode = e.code

else:

sys.stderr.write(str(e.code) + '\n')

exitcode = 1

except:

exitcode = 1

import traceback

sys.stderr.write('Process %s:\n' % self.name)

traceback.print_exc()

finally:

threading._shutdown()

util.info('process exiting with exitcode %d' % exitcode)

util._flush_std_streams()

return exitcode

@staticmethod

def _after_fork():

from . import util

util._finalizer_registry.clear()

util._run_after_forkers()

#

# We subclass bytes to avoid accidental transmission of auth keys over network

#

class AuthenticationString(bytes):

def __reduce__(self):

from .context import get_spawning_popen

if get_spawning_popen() is None:

raise TypeError(

'Pickling an AuthenticationString object is '

'disallowed for security reasons'

)

return AuthenticationString, (bytes(self),)

#

# Create object representing the parent process

#

class _ParentProcess(BaseProcess):

def __init__(self, name, pid, sentinel):

self._identity = ()

self._name = name

self._pid = pid

self._parent_pid = None

self._popen = None

self._closed = False

self._sentinel = sentinel

self._config = {}

def is_alive(self):

from multiprocessing.connection import wait

return not wait([self._sentinel], timeout=0)

@property

def ident(self):

return self._pid

def join(self, timeout=None):

'''

Wait until parent process terminates

'''

from multiprocessing.connection import wait

wait([self._sentinel], timeout=timeout)

pid = ident

#

# Create object representing the main process

#

class _MainProcess(BaseProcess):

def __init__(self):

self._identity = ()

self._name = 'MainProcess'

self._parent_pid = None

self._popen = None

self._closed = False

self._config = {'authkey': AuthenticationString(os.urandom(32)),

'semprefix': '/mp'}

# Note that some versions of FreeBSD only allow named

# semaphores to have names of up to 14 characters. Therefore

# we choose a short prefix.

#

# On MacOSX in a sandbox it may be necessary to use a

# different prefix -- see #19478.

#

# Everything in self._config will be inherited by descendant

# processes.

def close(self):

pass

_parent_process = None

_current_process = _MainProcess()

_process_counter = itertools.count(1)

_children = set()

del _MainProcess

#

# Give names to some return codes

#

_exitcode_to_name = {}

for name, signum in list(signal.__dict__.items()):

if name[:3]=='SIG' and '_' not in name:

_exitcode_to_name[-signum] = f'-{name}'

del name, signum

# For debug and leak testing

_dangling = WeakSet()