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Diffstat (limited to 'lib/python2.7/_threading_local.py')
| -rw-r--r-- | lib/python2.7/_threading_local.py | 251 |
1 files changed, 251 insertions, 0 deletions
diff --git a/lib/python2.7/_threading_local.py b/lib/python2.7/_threading_local.py new file mode 100644 index 0000000..09a3515 --- /dev/null +++ b/lib/python2.7/_threading_local.py @@ -0,0 +1,251 @@ +"""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 sure we don't call it + # again ourselves. + dict = object.__getattribute__(self, '__dict__') + current_thread().__dict__[key] = dict + + return self + +def _patch(self): + key = object.__getattribute__(self, '_local__key') + d = current_thread().__dict__.get(key) + if d is None: + d = {} + current_thread().__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): + if name == '__dict__': + raise AttributeError( + "%r object attribute '__dict__' is read-only" + % self.__class__.__name__) + lock = object.__getattribute__(self, '_local__lock') + lock.acquire() + try: + _patch(self) + return object.__setattr__(self, name, value) + finally: + lock.release() + + def __delattr__(self, name): + if name == '__dict__': + raise AttributeError( + "%r object attribute '__dict__' is read-only" + % self.__class__.__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: + # We use the non-locking API since we might already hold the lock + # (__del__ can be called at any point by the cyclic GC). + threads = threading._enumerate() + except: + # If enumerating the current threads 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 current_thread, RLock |