Viewing file: _threading_local.py (4.26 KB) -rw-r--r-- Select action/file-type: (+) | (+) | (+) | Code (+) | Session (+) | (+) | SDB (+) | (+) | (+) | (+) | (+) | (+) |
"""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`.) """
from weakref import ref from contextlib import contextmanager
__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 all platforms on CPython 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.
class _localimpl: """A class managing thread-local dicts""" __slots__ = 'key', 'dicts', 'localargs', 'locallock', '__weakref__'
def __init__(self): # The key used in the Thread objects' attribute dicts. # We keep it a string for speed but make it unlikely to clash with # a "real" attribute. self.key = '_threading_local._localimpl.' + str(id(self)) # { id(Thread) -> (ref(Thread), thread-local dict) } self.dicts = {}
def get_dict(self): """Return the dict for the current thread. Raises KeyError if none defined.""" thread = current_thread() return self.dicts[id(thread)][1]
def create_dict(self): """Create a new dict for the current thread, and return it.""" localdict = {} key = self.key thread = current_thread() idt = id(thread) def local_deleted(_, key=key): # When the localimpl is deleted, remove the thread attribute. thread = wrthread() if thread is not None: del thread.__dict__[key] def thread_deleted(_, idt=idt): # When the thread is deleted, remove the local dict. # Note that this is suboptimal if the thread object gets # caught in a reference loop. We would like to be called # as soon as the OS-level thread ends instead. local = wrlocal() if local is not None: dct = local.dicts.pop(idt) wrlocal = ref(self, local_deleted) wrthread = ref(thread, thread_deleted) thread.__dict__[key] = wrlocal self.dicts[idt] = wrthread, localdict return localdict
@contextmanager def _patch(self): impl = object.__getattribute__(self, '_local__impl') try: dct = impl.get_dict() except KeyError: dct = impl.create_dict() args, kw = impl.localargs self.__init__(*args, **kw) with impl.locallock: object.__setattr__(self, '__dict__', dct) yield
class local: __slots__ = '_local__impl', '__dict__'
def __new__(cls, /, *args, **kw): if (args or kw) and (cls.__init__ is object.__init__): raise TypeError("Initialization arguments are not supported") self = object.__new__(cls) impl = _localimpl() impl.localargs = (args, kw) impl.locallock = RLock() object.__setattr__(self, '_local__impl', impl) # We need to create the thread dict in anticipation of # __init__ being called, to make sure we don't call it # again ourselves. impl.create_dict() return self
def __getattribute__(self, name): with _patch(self): return object.__getattribute__(self, name)
def __setattr__(self, name, value): if name == '__dict__': raise AttributeError( "%r object attribute '__dict__' is read-only" % self.__class__.__name__) with _patch(self): return object.__setattr__(self, name, value)
def __delattr__(self, name): if name == '__dict__': raise AttributeError( "%r object attribute '__dict__' is read-only" % self.__class__.__name__) with _patch(self): return object.__delattr__(self, name)
from threading import current_thread, RLock
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