# Copyright 2015 Huawei Technologies Co., Ltd.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from threading import Lock


class Singleton(object):
    def __init__(self, factory_method):
        self._factory_method = factory_method
        self._instance = None
        self._instanceLock = Lock()

    def get_instance(self):
        if self._instance is None:
            with self._instanceLock:
                if self._instance is None:
                    self._instance = self._factory_method()

        return self._instance