单例模式实现的几种方式--Python

方案一

from functools import wraps
from threading import Lock


def singleton(cls):
    """线程安全单例"""
    instance = {}
    lock = Lock()

    @wraps(cls)
    def wrapper(*args, **kwargs):
        if cls not in instance:
            with lock:
                # 再次检查是否有实例
                if cls not in instance:
                    instance[cls] = cls(*args, **kwargs)
        return instance[cls]

    return wrapper

方案二

class Singleton:
    lock = threading.Lock()

    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, "_instance"):
            with cls.lock:
                if not hasattr(cls, "_instance"):
                    cls._instance = super().__new__(cls, *args, **kwargs)
        return cls._instance

方案三

class SingletonMeta(type):
    def __init__(cls, *args, **kwargs):
        cls.__instance = None
        cls.__lock = RLock()

    def __call__(cls, *args, **kwargs):
        if not cls.__instance:
            with cls.__lock:
                if not cls.__instance:
                    cls.__instance = super().__call__(*args, **kwargs)
        return cls.__instance