242 lines
7.0 KiB
Python
242 lines
7.0 KiB
Python
"""Thread-local objects.
|
|
|
|
(Note that this module provides a Python version of the 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:
|
|
|
|
>>> mydata = local()
|
|
>>> mydata.number = 42
|
|
>>> mydata.number
|
|
42
|
|
|
|
You can also access the local-object's dictionary:
|
|
|
|
>>> mydata.__dict__
|
|
{'number': 42}
|
|
>>> mydata.__dict__.setdefault('widgets', [])
|
|
[]
|
|
>>> mydata.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:
|
|
|
|
>>> log = []
|
|
>>> def f():
|
|
... items = mydata.__dict__.items()
|
|
... items.sort()
|
|
... log.append(items)
|
|
... mydata.number = 11
|
|
... log.append(mydata.number)
|
|
|
|
>>> import threading
|
|
>>> thread = threading.Thread(target=f)
|
|
>>> thread.start()
|
|
>>> thread.join()
|
|
>>> log
|
|
[[], 11]
|
|
|
|
we get different data. Furthermore, changes made in the other thread
|
|
don't affect data seen in this thread:
|
|
|
|
>>> mydata.number
|
|
42
|
|
|
|
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
|
|
came from.
|
|
|
|
You can create custom local objects by subclassing the local class:
|
|
|
|
>>> class MyLocal(local):
|
|
... number = 2
|
|
... initialized = False
|
|
... def __init__(self, **kw):
|
|
... if self.initialized:
|
|
... raise SystemError('__init__ called too many times')
|
|
... self.initialized = True
|
|
... self.__dict__.update(kw)
|
|
... def squared(self):
|
|
... 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:
|
|
|
|
>>> mydata.number
|
|
2
|
|
|
|
an initial color:
|
|
|
|
>>> mydata.color
|
|
'red'
|
|
>>> del mydata.color
|
|
|
|
And a method that operates on the data:
|
|
|
|
>>> mydata.squared()
|
|
4
|
|
|
|
As before, we can access the data in a separate thread:
|
|
|
|
>>> log = []
|
|
>>> thread = threading.Thread(target=f)
|
|
>>> thread.start()
|
|
>>> thread.join()
|
|
>>> log
|
|
[[('color', 'red'), ('initialized', True)], 11]
|
|
|
|
without affecting this thread's data:
|
|
|
|
>>> mydata.number
|
|
2
|
|
>>> mydata.color
|
|
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):
|
|
... __slots__ = 'number'
|
|
|
|
>>> mydata = MyLocal()
|
|
>>> mydata.number = 42
|
|
>>> mydata.color = 'red'
|
|
|
|
So, the separate thread:
|
|
|
|
>>> thread = threading.Thread(target=f)
|
|
>>> thread.start()
|
|
>>> thread.join()
|
|
|
|
affects what we see:
|
|
|
|
>>> mydata.number
|
|
11
|
|
|
|
>>> del mydata
|
|
"""
|
|
|
|
__all__ = ["local"]
|
|
|
|
# We need to use objects from the threading module, but the threading
|
|
# module may also want to use our `local` class, if support for locals
|
|
# isn't compiled in to the `thread` module. This creates potential problems
|
|
# with circular imports. For that reason, we don't import `threading`
|
|
# until the bottom of this file (a hack sufficient to worm around the
|
|
# potential problems). Note that almost all platforms do have support for
|
|
# locals in the `thread` module, and there is no circular import problem
|
|
# then, so problems introduced by fiddling the order of imports here won't
|
|
# manifest on most boxes.
|
|
|
|
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
|
|
# again ourselves.
|
|
dict = object.__getattribute__(self, '__dict__')
|
|
currentThread().__dict__[key] = dict
|
|
|
|
return self
|
|
|
|
def _patch(self):
|
|
key = object.__getattribute__(self, '_local__key')
|
|
d = currentThread().__dict__.get(key)
|
|
if d is None:
|
|
d = {}
|
|
currentThread().__dict__[key] = d
|
|
object.__setattr__(self, '__dict__', d)
|
|
|
|
# we have a new instance dict, so call out __init__ if we have
|
|
# one
|
|
cls = type(self)
|
|
if cls.__init__ is not object.__init__:
|
|
args, kw = object.__getattribute__(self, '_local__args')
|
|
cls.__init__(self, *args, **kw)
|
|
else:
|
|
object.__setattr__(self, '__dict__', d)
|
|
|
|
class local(_localbase):
|
|
|
|
def __getattribute__(self, name):
|
|
lock = object.__getattribute__(self, '_local__lock')
|
|
lock.acquire()
|
|
try:
|
|
_patch(self)
|
|
return object.__getattribute__(self, name)
|
|
finally:
|
|
lock.release()
|
|
|
|
def __setattr__(self, name, value):
|
|
lock = object.__getattribute__(self, '_local__lock')
|
|
lock.acquire()
|
|
try:
|
|
_patch(self)
|
|
return object.__setattr__(self, name, value)
|
|
finally:
|
|
lock.release()
|
|
|
|
def __delattr__(self, name):
|
|
lock = object.__getattribute__(self, '_local__lock')
|
|
lock.acquire()
|
|
try:
|
|
_patch(self)
|
|
return object.__delattr__(self, name)
|
|
finally:
|
|
lock.release()
|
|
|
|
def __del__(self):
|
|
import threading
|
|
|
|
key = object.__getattribute__(self, '_local__key')
|
|
|
|
try:
|
|
threads = list(threading.enumerate())
|
|
except:
|
|
# If enumerate fails, as it seems to do during
|
|
# shutdown, we'll skip cleanup under the assumption
|
|
# that there is nothing to clean up.
|
|
return
|
|
|
|
for thread in threads:
|
|
try:
|
|
__dict__ = thread.__dict__
|
|
except AttributeError:
|
|
# Thread is dying, rest in peace.
|
|
continue
|
|
|
|
if key in __dict__:
|
|
try:
|
|
del __dict__[key]
|
|
except KeyError:
|
|
pass # didn't have anything in this thread
|
|
|
|
from threading import currentThread, RLock
|