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from threading import RLock

_missing = object()


class locked_cached_property(object):
"""A decorator that converts a function into a lazy property. The
function wrapped is called the first time to retrieve the result
and then that calculated result is used the next time you access
the value. Works like the one in Werkzeug but has a lock for
thread safety.
"""

def __init__(self, func, name=None, doc=None):
self.__name__ = name or func.__name__
self.__module__ = func.__module__
self.__doc__ = doc or func.__doc__
self.func = func
self.lock = RLock()

def __get__(self, obj, type=None):
if obj is None:
return self
with self.lock:
value = obj.__dict__.get(self.__name__, _missing)
if value is _missing:
value = self.func(obj)
obj.__dict__[self.__name__] = value
return value

In [27]: class B:
...: @locked_cached_property
...: def foo(self):
...: import time
...:
...: print('processing....')
...: time.sleep(10)
...: return 'b'
...:
...:

In [28]: b = B()

In [29]: b.foo
processing....
Out[29]: 'b'

In [30]: b.foo
Out[30]: 'b'

In [31]: