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@pitrou @vstinner @tomMoral @serhiy-storchaka @shibturn @applio @jdufresne @bombs-kim
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import os
import sys
import threading
from . import process
from . import reduction
__all__ = ()
# Exceptions
class ProcessError(Exception):
class BufferTooShort(ProcessError):
class TimeoutError(ProcessError):
class AuthenticationError(ProcessError):
# Base type for contexts. Bound methods of an instance of this type are included in __all__ of
class BaseContext(object):
ProcessError = ProcessError
BufferTooShort = BufferTooShort
TimeoutError = TimeoutError
AuthenticationError = AuthenticationError
current_process = staticmethod(process.current_process)
parent_process = staticmethod(process.parent_process)
active_children = staticmethod(process.active_children)
def cpu_count(self):
'''Returns the number of CPUs in the system'''
num = os.cpu_count()
if num is None:
raise NotImplementedError('cannot determine number of cpus')
return num
def Manager(self):
'''Returns a manager associated with a running server process
The managers methods such as `Lock()`, `Condition()` and `Queue()`
can be used to create shared objects.
from .managers import SyncManager
m = SyncManager(ctx=self.get_context())
return m
def Pipe(self, duplex=True):
'''Returns two connection object connected by a pipe'''
from .connection import Pipe
return Pipe(duplex)
def Lock(self):
'''Returns a non-recursive lock object'''
from .synchronize import Lock
return Lock(ctx=self.get_context())
def RLock(self):
'''Returns a recursive lock object'''
from .synchronize import RLock
return RLock(ctx=self.get_context())
def Condition(self, lock=None):
'''Returns a condition object'''
from .synchronize import Condition
return Condition(lock, ctx=self.get_context())
def Semaphore(self, value=1):
'''Returns a semaphore object'''
from .synchronize import Semaphore
return Semaphore(value, ctx=self.get_context())
def BoundedSemaphore(self, value=1):
'''Returns a bounded semaphore object'''
from .synchronize import BoundedSemaphore
return BoundedSemaphore(value, ctx=self.get_context())
def Event(self):
'''Returns an event object'''
from .synchronize import Event
return Event(ctx=self.get_context())
def Barrier(self, parties, action=None, timeout=None):
'''Returns a barrier object'''
from .synchronize import Barrier
return Barrier(parties, action, timeout, ctx=self.get_context())
def Queue(self, maxsize=0):
'''Returns a queue object'''
from .queues import Queue
return Queue(maxsize, ctx=self.get_context())
def JoinableQueue(self, maxsize=0):
'''Returns a queue object'''
from .queues import JoinableQueue
return JoinableQueue(maxsize, ctx=self.get_context())
def SimpleQueue(self):
'''Returns a queue object'''
from .queues import SimpleQueue
return SimpleQueue(ctx=self.get_context())
def Pool(self, processes=None, initializer=None, initargs=(),
'''Returns a process pool object'''
from .pool import Pool
return Pool(processes, initializer, initargs, maxtasksperchild,
def RawValue(self, typecode_or_type, *args):
'''Returns a shared object'''
from .sharedctypes import RawValue
return RawValue(typecode_or_type, *args)
def RawArray(self, typecode_or_type, size_or_initializer):
'''Returns a shared array'''
from .sharedctypes import RawArray
return RawArray(typecode_or_type, size_or_initializer)
def Value(self, typecode_or_type, *args, lock=True):
'''Returns a synchronized shared object'''
from .sharedctypes import Value
return Value(typecode_or_type, *args, lock=lock,
def Array(self, typecode_or_type, size_or_initializer, *, lock=True):
'''Returns a synchronized shared array'''
from .sharedctypes import Array
return Array(typecode_or_type, size_or_initializer, lock=lock,
def freeze_support(self):
'''Check whether this is a fake forked process in a frozen executable.
If so then run code specified by commandline and exit.
if sys.platform == 'win32' and getattr(sys, 'frozen', False):
from .spawn import freeze_support
def get_logger(self):
'''Return package logger -- if it does not already exist then
it is created.
from .util import get_logger
return get_logger()
def log_to_stderr(self, level=None):
'''Turn on logging and add a handler which prints to stderr'''
from .util import log_to_stderr
return log_to_stderr(level)
def allow_connection_pickling(self):
'''Install support for sending connections and sockets
between processes
# This is undocumented. In previous versions of multiprocessing
# its only effect was to make socket objects inheritable on Windows.
from . import connection
def set_executable(self, executable):
'''Sets the path to a python.exe or pythonw.exe binary used to run
child processes instead of sys.executable when using the 'spawn'
start method. Useful for people embedding Python.
from .spawn import set_executable
def set_forkserver_preload(self, module_names):
'''Set list of module names to try to load in forkserver process.
This is really just a hint.
from .forkserver import set_forkserver_preload
def get_context(self, method=None):
if method is None:
return self
ctx = _concrete_contexts[method]
except KeyError:
raise ValueError('cannot find context for %r' % method) from None
return ctx
def get_start_method(self, allow_none=False):
return self._name
def set_start_method(self, method, force=False):
raise ValueError('cannot set start method of concrete context')
def reducer(self):
'''Controls how objects will be reduced to a form that can be
shared with other processes.'''
return globals().get('reduction')
def reducer(self, reduction):
globals()['reduction'] = reduction
def _check_available(self):
# Type of default context -- underlying context can be set at most once
class Process(process.BaseProcess):
_start_method = None
def _Popen(process_obj):
return _default_context.get_context().Process._Popen(process_obj)
class DefaultContext(BaseContext):
Process = Process
def __init__(self, context):
self._default_context = context
self._actual_context = None
def get_context(self, method=None):
if method is None:
if self._actual_context is None:
self._actual_context = self._default_context
return self._actual_context
return super().get_context(method)
def set_start_method(self, method, force=False):
if self._actual_context is not None and not force:
raise RuntimeError('context has already been set')
if method is None and force:
self._actual_context = None
self._actual_context = self.get_context(method)
def get_start_method(self, allow_none=False):
if self._actual_context is None:
if allow_none:
return None
self._actual_context = self._default_context
return self._actual_context._name
def get_all_start_methods(self):
if sys.platform == 'win32':
return ['spawn']
if reduction.HAVE_SEND_HANDLE:
return ['fork', 'spawn', 'forkserver']
return ['fork', 'spawn']
# Context types for fixed start method
if sys.platform != 'win32':
class ForkProcess(process.BaseProcess):
_start_method = 'fork'
def _Popen(process_obj):
from .popen_fork import Popen
return Popen(process_obj)
class SpawnProcess(process.BaseProcess):
_start_method = 'spawn'
def _Popen(process_obj):
from .popen_spawn_posix import Popen
return Popen(process_obj)
class ForkServerProcess(process.BaseProcess):
_start_method = 'forkserver'
def _Popen(process_obj):
from .popen_forkserver import Popen
return Popen(process_obj)
class ForkContext(BaseContext):
_name = 'fork'
Process = ForkProcess
class SpawnContext(BaseContext):
_name = 'spawn'
Process = SpawnProcess
class ForkServerContext(BaseContext):
_name = 'forkserver'
Process = ForkServerProcess
def _check_available(self):
if not reduction.HAVE_SEND_HANDLE:
raise ValueError('forkserver start method not available')
_concrete_contexts = {
'fork': ForkContext(),
'spawn': SpawnContext(),
'forkserver': ForkServerContext(),
if sys.platform == 'darwin':
# bpo-33725: running arbitrary code after fork() is no longer reliable
# on macOS since macOS 10.14 (Mojave). Use spawn by default instead.
_default_context = DefaultContext(_concrete_contexts['spawn'])
_default_context = DefaultContext(_concrete_contexts['fork'])
class SpawnProcess(process.BaseProcess):
_start_method = 'spawn'
def _Popen(process_obj):
from .popen_spawn_win32 import Popen
return Popen(process_obj)
class SpawnContext(BaseContext):
_name = 'spawn'
Process = SpawnProcess
_concrete_contexts = {
'spawn': SpawnContext(),
_default_context = DefaultContext(_concrete_contexts['spawn'])
# Force the start method
def _force_start_method(method):
_default_context._actual_context = _concrete_contexts[method]
# Check that the current thread is spawning a child process
_tls = threading.local()
def get_spawning_popen():
return getattr(_tls, 'spawning_popen', None)
def set_spawning_popen(popen):
_tls.spawning_popen = popen
def assert_spawning(obj):
if get_spawning_popen() is None:
raise RuntimeError(
'%s objects should only be shared between processes'
' through inheritance' % type(obj).__name__
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