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162 lines
4.9 KiB
162 lines
4.9 KiB
"""
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单例模式 (Singleton Pattern)
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意图：确保一个类只有一个实例，并提供一个全局访问点。
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应用场景：
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- 资源管理器（如数据库连接池、线程池）
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- 配置管理器
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- 日志记录器
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- 全局计数器
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本实现提供了三种常见的单例模式实现方式：
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1. 懒汉式 (延迟初始化)
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2. 饿汉式 (立即初始化)
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3. 线程安全的懒汉式 (使用双重检查锁定)
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"""
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class LazySingleton:
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"""懒汉式单例 - 延迟初始化，非线程安全"""
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_instance = None
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def __new__(cls):
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if cls._instance is None:
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cls._instance = super(LazySingleton, cls).__new__(cls)
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# 初始化代码
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cls._instance.data = "Lazy Singleton Data"
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return cls._instance
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def do_something(self):
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"""演示单例的功能方法"""
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return f"{self.__class__.__name__} is doing something with {self.data}"
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class EagerSingleton:
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"""饿汉式单例 - 立即初始化，线程安全"""
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_instance = None
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# 在类加载时就创建实例
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def __new__(cls):
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if cls._instance is None:
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cls._instance = super(EagerSingleton, cls).__new__(cls)
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# 初始化代码
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cls._instance.data = "Eager Singleton Data"
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return cls._instance
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def do_something(self):
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"""演示单例的功能方法"""
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return f"{self.__class__.__name__} is doing something with {self.data}"
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import threading
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class ThreadSafeSingleton:
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"""线程安全的懒汉式单例 - 使用双重检查锁定模式"""
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_instance = None
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_lock = threading.RLock() # 使用可重入锁
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def __new__(cls):
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# 第一次检查，避免不必要的锁
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if cls._instance is None:
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# 获取锁
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with cls._lock:
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# 第二次检查，确保在等待锁的过程中没有其他线程创建实例
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if cls._instance is None:
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cls._instance = super(ThreadSafeSingleton, cls).__new__(cls)
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# 初始化代码
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cls._instance.data = "Thread Safe Singleton Data"
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return cls._instance
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def do_something(self):
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"""演示单例的功能方法"""
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return f"{self.__class__.__name__} is doing something with {self.data}"
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class Singleton:
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"""使用元类实现的单例模式"""
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_instance = None
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def __new__(cls, *args, **kwargs):
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if cls._instance is None:
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cls._instance = super(Singleton, cls).__new__(cls)
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return cls._instance
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def __init__(self, data=None):
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# 仅在第一次初始化时设置属性
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if not hasattr(self, 'initialized'):
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self.data = data or "Default Singleton Data"
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self.initialized = True
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def do_something(self):
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"""演示单例的功能方法"""
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return f"{self.__class__.__name__} is doing something with {self.data}"
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def test_thread_safety():
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"""测试线程安全性"""
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instances = []
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def create_instance():
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instances.append(ThreadSafeSingleton())
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# 创建多个线程同时实例化
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threads = []
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for _ in range(10):
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thread = threading.Thread(target=create_instance)
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threads.append(thread)
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thread.start()
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# 等待所有线程完成
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for thread in threads:
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thread.join()
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# 验证所有实例都是同一个对象
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first_id = id(instances[0])
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for instance in instances[1:]:
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assert id(instance) == first_id, "线程安全测试失败：创建了多个实例"
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print("线程安全测试通过：所有线程创建的是同一个实例")
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def main():
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"""演示各种单例实现"""
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print("=== 单例模式演示 ===")
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# 测试懒汉式单例
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print("\n1. 懒汉式单例测试：")
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s1 = LazySingleton()
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s2 = LazySingleton()
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print(f"s1 id: {id(s1)}, s2 id: {id(s2)}")
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print(f"s1 == s2: {s1 is s2}")
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print(s1.do_something())
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# 测试饿汉式单例
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print("\n2. 饿汉式单例测试：")
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s3 = EagerSingleton()
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s4 = EagerSingleton()
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print(f"s3 id: {id(s3)}, s4 id: {id(s4)}")
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print(f"s3 == s4: {s3 is s4}")
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print(s3.do_something())
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# 测试线程安全的懒汉式单例
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print("\n3. 线程安全单例测试：")
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test_thread_safety()
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s5 = ThreadSafeSingleton()
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s6 = ThreadSafeSingleton()
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print(f"s5 id: {id(s5)}, s6 id: {id(s6)}")
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print(f"s5 == s6: {s5 is s6}")
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print(s5.do_something())
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# 测试使用元类的单例
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print("\n4. 元类单例测试：")
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s7 = Singleton("Custom Data")
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s8 = Singleton("This should not change") # 第二次初始化不会改变数据
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print(f"s7 id: {id(s7)}, s8 id: {id(s8)}")
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print(f"s7 == s8: {s7 is s8}")
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print(f"s7.data: {s7.data}") # 应该是 "Custom Data"
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print(s7.do_something())
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if __name__ == "__main__":
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main() |