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ef5d00a592
Fix a race condition in the internal `multiprocessing.process` cleanup logic that could manifest as an unintended `AttributeError` when calling `BaseProcess.close()`. --------- Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net> Co-authored-by: Gregory P. Smith <greg@krypto.org>
439 lines
12 KiB
Python
439 lines
12 KiB
Python
#
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# Module providing the `Process` class which emulates `threading.Thread`
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#
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# multiprocessing/process.py
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#
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# Copyright (c) 2006-2008, R Oudkerk
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# Licensed to PSF under a Contributor Agreement.
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#
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__all__ = ['BaseProcess', 'current_process', 'active_children',
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'parent_process']
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#
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# Imports
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#
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import os
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import sys
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import signal
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import itertools
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import threading
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from _weakrefset import WeakSet
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#
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#
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#
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try:
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ORIGINAL_DIR = os.path.abspath(os.getcwd())
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except OSError:
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ORIGINAL_DIR = None
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#
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# Public functions
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#
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def current_process():
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'''
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Return process object representing the current process
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'''
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return _current_process
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def active_children():
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'''
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Return list of process objects corresponding to live child processes
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'''
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_cleanup()
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return list(_children)
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def parent_process():
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'''
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Return process object representing the parent process
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'''
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return _parent_process
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#
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#
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#
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def _cleanup():
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# check for processes which have finished
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for p in list(_children):
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if (child_popen := p._popen) and child_popen.poll() is not None:
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_children.discard(p)
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#
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# The `Process` class
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#
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class BaseProcess(object):
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'''
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Process objects represent activity that is run in a separate process
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The class is analogous to `threading.Thread`
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'''
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def _Popen(self):
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raise NotImplementedError
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def __init__(self, group=None, target=None, name=None, args=(), kwargs={},
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*, daemon=None):
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assert group is None, 'group argument must be None for now'
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count = next(_process_counter)
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self._identity = _current_process._identity + (count,)
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self._config = _current_process._config.copy()
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self._parent_pid = os.getpid()
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self._parent_name = _current_process.name
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self._popen = None
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self._closed = False
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self._target = target
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self._args = tuple(args)
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self._kwargs = dict(kwargs)
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self._name = name or type(self).__name__ + '-' + \
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':'.join(str(i) for i in self._identity)
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if daemon is not None:
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self.daemon = daemon
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_dangling.add(self)
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def _check_closed(self):
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if self._closed:
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raise ValueError("process object is closed")
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def run(self):
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'''
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Method to be run in sub-process; can be overridden in sub-class
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'''
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if self._target:
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self._target(*self._args, **self._kwargs)
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def start(self):
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'''
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Start child process
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'''
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self._check_closed()
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assert self._popen is None, 'cannot start a process twice'
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assert self._parent_pid == os.getpid(), \
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'can only start a process object created by current process'
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assert not _current_process._config.get('daemon'), \
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'daemonic processes are not allowed to have children'
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_cleanup()
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self._popen = self._Popen(self)
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self._sentinel = self._popen.sentinel
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# Avoid a refcycle if the target function holds an indirect
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# reference to the process object (see bpo-30775)
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del self._target, self._args, self._kwargs
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_children.add(self)
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def terminate(self):
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'''
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Terminate process; sends SIGTERM signal or uses TerminateProcess()
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'''
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self._check_closed()
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self._popen.terminate()
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def kill(self):
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'''
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Terminate process; sends SIGKILL signal or uses TerminateProcess()
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'''
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self._check_closed()
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self._popen.kill()
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def join(self, timeout=None):
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'''
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Wait until child process terminates
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'''
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self._check_closed()
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assert self._parent_pid == os.getpid(), 'can only join a child process'
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assert self._popen is not None, 'can only join a started process'
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res = self._popen.wait(timeout)
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if res is not None:
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_children.discard(self)
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def is_alive(self):
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'''
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Return whether process is alive
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'''
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self._check_closed()
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if self is _current_process:
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return True
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assert self._parent_pid == os.getpid(), 'can only test a child process'
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if self._popen is None:
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return False
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returncode = self._popen.poll()
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if returncode is None:
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return True
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else:
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_children.discard(self)
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return False
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def close(self):
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'''
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Close the Process object.
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This method releases resources held by the Process object. It is
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an error to call this method if the child process is still running.
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'''
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if self._popen is not None:
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if self._popen.poll() is None:
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raise ValueError("Cannot close a process while it is still running. "
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"You should first call join() or terminate().")
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self._popen.close()
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self._popen = None
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del self._sentinel
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_children.discard(self)
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self._closed = True
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@property
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def name(self):
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return self._name
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@name.setter
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def name(self, name):
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assert isinstance(name, str), 'name must be a string'
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self._name = name
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@property
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def daemon(self):
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'''
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Return whether process is a daemon
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'''
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return self._config.get('daemon', False)
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@daemon.setter
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def daemon(self, daemonic):
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'''
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Set whether process is a daemon
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'''
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assert self._popen is None, 'process has already started'
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self._config['daemon'] = daemonic
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@property
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def authkey(self):
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return self._config['authkey']
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@authkey.setter
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def authkey(self, authkey):
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'''
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Set authorization key of process
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'''
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self._config['authkey'] = AuthenticationString(authkey)
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@property
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def exitcode(self):
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'''
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Return exit code of process or `None` if it has yet to stop
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'''
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self._check_closed()
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if self._popen is None:
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return self._popen
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return self._popen.poll()
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@property
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def ident(self):
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'''
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Return identifier (PID) of process or `None` if it has yet to start
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'''
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self._check_closed()
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if self is _current_process:
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return os.getpid()
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else:
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return self._popen and self._popen.pid
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pid = ident
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@property
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def sentinel(self):
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'''
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Return a file descriptor (Unix) or handle (Windows) suitable for
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waiting for process termination.
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'''
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self._check_closed()
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try:
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return self._sentinel
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except AttributeError:
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raise ValueError("process not started") from None
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def __repr__(self):
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exitcode = None
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if self is _current_process:
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status = 'started'
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elif self._closed:
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status = 'closed'
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elif self._parent_pid != os.getpid():
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status = 'unknown'
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elif self._popen is None:
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status = 'initial'
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else:
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exitcode = self._popen.poll()
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if exitcode is not None:
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status = 'stopped'
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else:
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status = 'started'
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info = [type(self).__name__, 'name=%r' % self._name]
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if self._popen is not None:
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info.append('pid=%s' % self._popen.pid)
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info.append('parent=%s' % self._parent_pid)
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info.append(status)
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if exitcode is not None:
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exitcode = _exitcode_to_name.get(exitcode, exitcode)
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info.append('exitcode=%s' % exitcode)
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if self.daemon:
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info.append('daemon')
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return '<%s>' % ' '.join(info)
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##
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def _bootstrap(self, parent_sentinel=None):
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from . import util, context
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global _current_process, _parent_process, _process_counter, _children
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try:
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if self._start_method is not None:
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context._force_start_method(self._start_method)
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_process_counter = itertools.count(1)
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_children = set()
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util._close_stdin()
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old_process = _current_process
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_current_process = self
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_parent_process = _ParentProcess(
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self._parent_name, self._parent_pid, parent_sentinel)
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if threading._HAVE_THREAD_NATIVE_ID:
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threading.main_thread()._set_native_id()
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try:
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self._after_fork()
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finally:
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# delay finalization of the old process object until after
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# _run_after_forkers() is executed
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del old_process
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util.info('child process calling self.run()')
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try:
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self.run()
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exitcode = 0
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finally:
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util._exit_function()
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except SystemExit as e:
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if e.code is None:
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exitcode = 0
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elif isinstance(e.code, int):
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exitcode = e.code
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else:
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sys.stderr.write(str(e.code) + '\n')
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exitcode = 1
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except:
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exitcode = 1
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import traceback
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sys.stderr.write('Process %s:\n' % self.name)
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traceback.print_exc()
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finally:
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threading._shutdown()
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util.info('process exiting with exitcode %d' % exitcode)
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util._flush_std_streams()
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return exitcode
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@staticmethod
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def _after_fork():
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from . import util
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util._finalizer_registry.clear()
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util._run_after_forkers()
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#
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# We subclass bytes to avoid accidental transmission of auth keys over network
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#
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class AuthenticationString(bytes):
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def __reduce__(self):
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from .context import get_spawning_popen
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if get_spawning_popen() is None:
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raise TypeError(
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'Pickling an AuthenticationString object is '
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'disallowed for security reasons'
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)
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return AuthenticationString, (bytes(self),)
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#
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# Create object representing the parent process
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#
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class _ParentProcess(BaseProcess):
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def __init__(self, name, pid, sentinel):
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self._identity = ()
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self._name = name
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self._pid = pid
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self._parent_pid = None
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self._popen = None
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self._closed = False
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self._sentinel = sentinel
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self._config = {}
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def is_alive(self):
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from multiprocessing.connection import wait
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return not wait([self._sentinel], timeout=0)
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@property
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def ident(self):
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return self._pid
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def join(self, timeout=None):
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'''
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Wait until parent process terminates
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'''
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from multiprocessing.connection import wait
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wait([self._sentinel], timeout=timeout)
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pid = ident
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#
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# Create object representing the main process
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#
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class _MainProcess(BaseProcess):
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def __init__(self):
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self._identity = ()
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self._name = 'MainProcess'
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self._parent_pid = None
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self._popen = None
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self._closed = False
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self._config = {'authkey': AuthenticationString(os.urandom(32)),
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'semprefix': '/mp'}
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# Note that some versions of FreeBSD only allow named
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# semaphores to have names of up to 14 characters. Therefore
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# we choose a short prefix.
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#
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# On MacOSX in a sandbox it may be necessary to use a
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# different prefix -- see #19478.
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#
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# Everything in self._config will be inherited by descendant
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# processes.
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def close(self):
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pass
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_parent_process = None
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_current_process = _MainProcess()
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_process_counter = itertools.count(1)
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_children = set()
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del _MainProcess
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#
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# Give names to some return codes
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#
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_exitcode_to_name = {}
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for name, signum in list(signal.__dict__.items()):
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if name[:3]=='SIG' and '_' not in name:
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_exitcode_to_name[-signum] = f'-{name}'
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del name, signum
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# For debug and leak testing
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_dangling = WeakSet()
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