c90fde06538420e273923aef3df597ddd5aceaa8
(Note that this module provides a Python version of thread
threading.local class. Depending on the version of Python you're
using, there may be a faster one available. You should always import
the local class from threading.)
Thread-local objects support the management of thread-local data.
If you have data that you want to be local to a thread, simply create
a thread-local object and use its attributes:
You can also access the local-object's dictionary:
>>> mydata.__dict__.setdefault('widgets', [])
What's important about thread-local objects is that their data are
local to a thread. If we access the data in a different thread:
... items = mydata.__dict__.items()
... log.append(mydata.number)
>>> thread = threading.Thread(target=f)
we get different data. Furthermore, changes made in the other thread
don't affect data seen in this thread:
Of course, values you get from a local object, including a __dict__
attribute, are for whatever thread was current at the time the
attribute was read. For that reason, you generally don't want to save
these values across threads, as they apply only to the thread they
You can create custom local objects by subclassing the local class:
>>> class MyLocal(local):
... def __init__(self, **kw):
... raise SystemError('__init__ called too many times')
... self.initialized = True
... self.__dict__.update(kw)
... return self.number ** 2
This can be useful to support default values, methods and
initialization. Note that if you define an __init__ method, it will be
called each time the local object is used in a separate thread. This
is necessary to initialize each thread's dictionary.
Now if we create a local object:
>>> mydata = MyLocal(color='red')
Now we have a default number:
And a method that operates on the data:
As before, we can access the data in a separate thread:
>>> thread = threading.Thread(target=f)
[[('color', 'red'), ('initialized', True)], 11]
without affecting this thread's data:
Traceback (most recent call last):
AttributeError: 'MyLocal' object has no attribute 'color'
Note that subclasses can define slots, but they are not thread
local. They are shared across threads:
>>> class MyLocal(local):
>>> thread = threading.Thread(target=f)
# Threading import is at end
class _localbase(object):
__slots__
= '_local__key', '_local__args', '_local__lock'
def __new__(cls
, *args
, **kw
):
self
= object.__new
__(cls
)
key
= '_local__key', 'thread.local.' + str(id(self
))
object.__setattr
__(self
, '_local__key', key
)
object.__setattr
__(self
, '_local__args', (args
, kw
))
object.__setattr
__(self
, '_local__lock', RLock())
if args
or kw
and (cls
.__init
__ is object.__init
__):
raise TypeError("Initialization arguments are not supported")
# We need to create the thread dict in anticipation of
# __init__ being called, to make sire we don't cal it
dict = object.__getattribute
__(self
, '__dict__')
currentThread().__dict
__[key
] = dict
key
= object.__getattribute
__(self
, '_local__key')
d
= currentThread().__dict
__.get(key
)
currentThread().__dict
__[key
] = d
object.__setattr
__(self
, '__dict__', d
)
# we have a new instance dict, so call out __init__ if we have
if cls
.__init
__ is not object.__init
__:
args
, kw
= object.__getattribute
__(self
, '_local__args')
cls
.__init
__(self
, *args
, **kw
)
object.__setattr
__(self
, '__dict__', d
)
def __getattribute__(self
, name
):
lock
= object.__getattribute
__(self
, '_local__lock')
return object.__getattribute
__(self
, name
)
def __setattr__(self
, name
, value
):
lock
= object.__getattribute
__(self
, '_local__lock')
return object.__setattr
__(self
, name
, value
)
def __delattr__(self
, name
):
lock
= object.__getattribute
__(self
, '_local__lock')
return object.__delattr
__(self
, name
)
threading_enumerate
= enumerate
__getattribute__
= object.__getattribute
__
key
= __getattribute__(self
, '_local__key')
threads
= list(threading_enumerate())
# if enumerate fails, as it seems to do during
# shutdown, we'll skip cleanup under the assumption
# that there is nothing to clean up
__dict__
= thread
.__dict
__
# Thread is dying, rest in peace
pass # didn't have anything in this thread
from threading
import currentThread
, enumerate, RLock