skywalking/utils/singleton.py

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You 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.
#


class Singleton(object):
    """
    This is to ensure a single process can only have one instance of agent.
    Written by Guido van Rossum to implement a singleton pattern.
    https://www.python.org/download/releases/2.2/descrintro/#__new__
    Classes that inherit from this class will be singletons.
    """
    def __new__(cls, *args, **kwds):
        it = cls.__dict__.get('__it__')
        if it is not None:
            return it
        cls.__it__ = it = object.__new__(cls)
        it.init(*args, **kwds)
        return it

    def init(self, *args, **kwds):
        pass