Source code for pds4_tools.extern.cached_property

# Copyright (c) 2015, Daniel Greenfeld
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
#     * Redistributions of source code must retain the above copyright
#        notice, this list of conditions and the following disclaimer.
#
#     * Redistributions in binary form must reproduce the above
#        copyright notice, this list of conditions and the following
#        disclaimer in the documentation and/or other materials provided
#        with the distribution.
#
#     * Neither the name of cached-property nor the names of its
#        contributors may be used to endorse or promote products derived
#        from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# -*- coding: utf-8 -*-

__author__ = 'Daniel Greenfeld'
__email__ = 'pydanny@gmail.com'
__version__ = '1.3.0'
__license__ = 'BSD'

from time import time
import threading


class cached_property(object):
    """
    A property that is only computed once per instance and then replaces itself
    with an ordinary attribute. Deleting the attribute resets the property.

    Source: https://github.com/bottlepy/bottle/commit/fa7733e075da0d790d809aa3d2f53071897e6f76
    """  # noqa

    def __init__(self, func):
        self.__doc__ = getattr(func, '__doc__')
        self.func = func

    def __get__(self, obj, cls):
        if obj is None:
            return self
        value = obj.__dict__[self.func.__name__] = self.func(obj)
        return value


class threaded_cached_property(object):
    """
    A cached_property version for use in environments where multiple threads
    might concurrently try to access the property.
    """

    def __init__(self, func):
        self.__doc__ = getattr(func, '__doc__')
        self.func = func
        self.lock = threading.RLock()

    def __get__(self, obj, cls):
        if obj is None:
            return self

        obj_dict = obj.__dict__
        name = self.func.__name__
        with self.lock:
            try:
                # check if the value was computed before the lock was acquired
                return obj_dict[name]
            except KeyError:
                # if not, do the calculation and release the lock
                return obj_dict.setdefault(name, self.func(obj))