# Copyright (c) 2023 PaddlePaddle Authors. All Rights Reserved.
#
# 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.

import threading
from typing import ClassVar

__all__ = ["Singleton"]


class Singleton(type):
    _insts: ClassVar[dict] = {}
    _lock = threading.Lock()

    def __call__(cls, *args, **kwargs):
        if cls not in cls._insts:
            with cls._lock:
                if cls not in cls._insts:
                    cls._insts[cls] = super().__call__(*args, **kwargs)
        return cls._insts[cls]