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from .util import threading
import weakref
class NameRegistry(object):
"""Generates and return an object, keeping it as a
singleton for a certain identifier for as long as its
strongly referenced.
.. note::
The :class:`.NameRegistry` exists here to support
certain usage patterns by the deprecated
:class:`.Dogpile` object. It is still potentially
useful in other cases, however.
e.g.::
class MyFoo(object):
"some important object."
def __init__(self, identifier):
self.identifier = identifier
registry = NameRegistry(MyFoo)
# thread 1:
my_foo = registry.get("foo1")
# thread 2
my_foo = registry.get("foo1")
Above, ``my_foo`` in both thread #1 and #2 will
be *the same object*. The constructor for
``MyFoo`` will be called once, passing the
identifier ``foo1`` as the argument.
When thread 1 and thread 2 both complete or
otherwise delete references to ``my_foo``, the
object is *removed* from the :class:`.NameRegistry` as
a result of Python garbage collection.
:class:`.NameRegistry` is a utility object that
is used to maintain new :class:`.Dogpile` objects
against a certain key, for as long as that particular key
is referenced within the application. An application
can deal with an arbitrary number of keys, ensuring that
all threads requesting a certain key use the same
:class:`.Dogpile` object, without the need to maintain
each :class:`.Dogpile` object persistently in memory.
:param creator: A function that will create a new
value, given the identifier passed to the :meth:`.NameRegistry.get`
method.
"""
_locks = weakref.WeakValueDictionary()
_mutex = threading.RLock()
def __init__(self, creator):
"""Create a new :class:`.NameRegistry`.
"""
self._values = weakref.WeakValueDictionary()
self._mutex = threading.RLock()
self.creator = creator
def get(self, identifier, *args, **kw):
"""Get and possibly create the value.
:param identifier: Hash key for the value.
If the creation function is called, this identifier
will also be passed to the creation function.
:param \*args, \**kw: Additional arguments which will
also be passed to the creation function if it is
called.
"""
try:
if identifier in self._values:
return self._values[identifier]
else:
return self._sync_get(identifier, *args, **kw)
except KeyError:
return self._sync_get(identifier, *args, **kw)
def _sync_get(self, identifier, *args, **kw):
self._mutex.acquire()
try:
try:
if identifier in self._values:
return self._values[identifier]
else:
self._values[identifier] = value = self.creator(identifier, *args, **kw)
return value
except KeyError:
self._values[identifier] = value = self.creator(identifier, *args, **kw)
return value
finally:
self._mutex.release()
|
