###########################################################################
#
# Copyright (c) 2019-2021 Diality Inc. - All Rights Reserved.
#
# THIS CODE MAY NOT BE COPIED OR REPRODUCED IN ANY FORM, IN PART OR IN
# WHOLE, WITHOUT THE EXPLICIT PERMISSION OF THE COPYRIGHT OWNER.
#
# @file    singleton.py
#
# @author  (last)      Quang Nguyen
# @date    (last)      19-Jul-2021
# @author  (original)  Peter Lucia
# @date    (original)  29-Apr-2021
#
############################################################################
from threading import Lock


class SingletonMeta(type):
    """
    Thread-safe implementation of Singleton.
    """

    _instances = {}

    _lock: Lock = Lock()
    _creation_attempts = 0
    """
    Synchronizes threads during first access to the Singleton.
    """

    def __call__(cls, *args, **kwargs):
        """
        Possible changes to the value of the `__init__` argument do not affect
        the returned instance.
        """
        cls._creation_attempts += 1
        # TODO: Remove later - keep for debugging
        # print("CAN interface constructor call counter: {0}".format(cls._creation_attempts))
        # First thread acquires the lock
        with cls._lock:
            if cls not in cls._instances:
                instance = super().__call__(*args, **kwargs)
                cls._instances[cls] = instance
        return cls._instances[cls]