单例模式的核心思想

单例模式确保一个类只有一个实例，并提供一个全局访问点。这在需要控制资源访问（如配置文件、数据库连接等）时非常有用。

一个简单的示例：

import threading
import time


class Singleton:
    instance = None
    lock = threading.RLock()  # 加锁（递归锁）防止并发创建新对象

    def __init__(self, name):
        self.name = name

    def __new__(cls, *args, **kwargs):
        if cls.instance:
            return cls.instance
        # 加锁
        with cls.lock:
            time.sleep(0.5)
            if cls.instance:
                return cls.instance
            cls.instance = object.__new__(cls)  # 创建空对象
            return cls.instance


# obj1 = Singleton('obj1')
# print(obj1)
# obj2 = Singleton('obj2')
# print(obj2)

def task():
    obj = Singleton('x')
    print(obj)


for i in range(10):
    t = threading.Thread(target=task)
    t.start()

"""
输出：
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>
<__main__.Singleton object at 0x0000024AFD72C090>

"""