深入探讨发布订阅模式的精简实现，从8行到3行，揭秘精简背后的玄机

2023-11-17 15:33:14

发布订阅模式简介

发布订阅模式是一种消息传递模式，允许发布者将消息发布到频道，而订阅者可以订阅该频道以接收消息。发布者和订阅者之间没有直接的耦合，这使得发布订阅模式非常灵活和可扩展。

3行实现

发布订阅模式最简单的实现只需要3行代码：

class Publisher:
    def __init__(self):
        self.subscribers = []

    def publish(self, message):
        for subscriber in self.subscribers:
            subscriber.receive(message)

class Subscriber:
    def __init__(self, publisher):
        publisher.subscribers.append(self)

    def receive(self, message):
        print(message)

# 创建发布者和订阅者
publisher = Publisher()
subscriber1 = Subscriber(publisher)
subscriber2 = Subscriber(publisher)

# 发布消息
publisher.publish("Hello, world!")

在这个实现中，Publisher类包含一个subscribers列表，其中存储了所有订阅者的引用。当发布者调用publish()方法时，它会遍历subscribers列表，并调用每个订阅者的receive()方法。

6行实现

6行实现与3行实现非常相似，但它增加了对主题的支持。主题允许订阅者只订阅感兴趣的消息。

class Publisher:
    def __init__(self):
        self.subscribers = {}

    def publish(self, topic, message):
        for subscriber in self.subscribers.get(topic, []):
            subscriber.receive(message)

class Subscriber:
    def __init__(self, publisher):
        self.publisher = publisher
        self.topics = []

    def subscribe(self, topic):
        self.topics.append(topic)
        self.publisher.subscribers.setdefault(topic, []).append(self)

    def receive(self, message):
        print(message)

# 创建发布者和订阅者
publisher = Publisher()
subscriber1 = Subscriber(publisher)
subscriber2 = Subscriber(publisher)

# 订阅者1订阅主题"topic1"
subscriber1.subscribe("topic1")

# 订阅者2订阅主题"topic2"
subscriber2.subscribe("topic2")

# 发布消息
publisher.publish("topic1", "Hello, world!")
publisher.publish("topic2", "Good morning!")

在这个实现中，Publisher类包含一个subscribers字典，其中存储了主题与订阅者列表的映射。当发布者调用publish()方法时，它会查找指定主题的订阅者列表，并调用每个订阅者的receive()方法。

8行实现

8行实现与6行实现非常相似，但它增加了对质量服务(QoS)的支持。QoS允许订阅者指定他们希望接收的消息的质量级别。

class Publisher:
    def __init__(self):
        self.subscribers = {}

    def publish(self, topic, message, qos):
        for subscriber in self.subscribers.get(topic, []):
            if subscriber.qos >= qos:
                subscriber.receive(message)

class Subscriber:
    def __init__(self, publisher):
        self.publisher = publisher
        self.topics = []
        self.qos = 1

    def subscribe(self, topic, qos):
        self.topics.append(topic)
        self.publisher.subscribers.setdefault(topic, []).append(self)
        self.qos = qos

    def receive(self, message):
        print(message)

# 创建发布者和订阅者
publisher = Publisher()
subscriber1 = Subscriber(publisher)
subscriber2 = Subscriber(publisher)

# 订阅者1订阅主题"topic1"，并设置QoS为2
subscriber1.subscribe("topic1", 2)

# 订阅者2订阅主题"topic2"，并设置QoS为1
subscriber2.subscribe("topic2", 1)

# 发布消息
publisher.publish("topic1", "Hello, world!", 2)
publisher.publish("topic2", "Good morning!", 1)