C語言發布訂閱模式詳解與實踐

1. 什么是發布訂閱模式？

發布訂閱模式定義了一種一對多的依賴關系，讓多個訂閱者對象同時監聽某一個主題。這個主題在狀態發生變化時，會通知所有依賴于它的訂閱者對象，使它們能夠自動更新。

2. 為什么需要發布訂閱模式？

• 實現對象間的松耦合
• 支持廣播通信
• 動態訂閱和取消訂閱
• 事件驅動架構
• 異步消息處理

3. 實際應用場景

• 傳感器數據分發
• 消息隊列系統
• 事件處理系統
• 日志監控
• 狀態更新通知

4. 代碼實現

4.1 UML 關系圖

4.2 頭文件 (pubsub.h)

#ifndef PUBSUB_H
#define PUBSUB_H#include <stdint.h>
#include <stdbool.h>// 主題數據結構
typedef struct {char name[32];          // 主題名稱void* data;            // 主題數據uint32_t data_size;    // 數據大小uint32_t timestamp;    // 時間戳
} Topic;// 訂閱者回調函數類型
typedef void (*SubscriberCallback)(const Topic* topic, void* user_data);// 訂閱者結構
typedef struct {char name[32];              // 訂閱者名稱SubscriberCallback callback; // 回調函數void* user_data;            // 用戶數據
} Subscriber;// 發布者結構
typedef struct {char name[32];              // 發布者名稱Subscriber* subscribers[16]; // 訂閱者列表int subscriber_count;       // 訂閱者數量
} Publisher;// 創建發布者
Publisher* create_publisher(const char* name);// 銷毀發布者
void destroy_publisher(Publisher* publisher);// 訂閱主題
bool subscribe(Publisher* publisher, const char* subscriber_name,SubscriberCallback callback,void* user_data);// 取消訂閱
bool unsubscribe(Publisher* publisher, const char* subscriber_name);// 發布主題
void publish(Publisher* publisher, const Topic* topic);#endif // PUBSUB_H

4.3 實現文件 (pubsub.c)

#include "pubsub.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>Publisher* create_publisher(const char* name) {Publisher* publisher = (Publisher*)malloc(sizeof(Publisher));strncpy(publisher->name, name, sizeof(publisher->name) - 1);publisher->subscriber_count = 0;memset(publisher->subscribers, 0, sizeof(publisher->subscribers));return publisher;
}void destroy_publisher(Publisher* publisher) {if (!publisher) return;// 釋放所有訂閱者for (int i = 0; i < publisher->subscriber_count; i++) {free(publisher->subscribers[i]);}free(publisher);
}bool subscribe(Publisher* publisher, const char* subscriber_name,SubscriberCallback callback,void* user_data) {if (!publisher || !subscriber_name || !callback) return false;// 檢查是否已達到最大訂閱者數量if (publisher->subscriber_count >= 16) {printf("訂閱者數量已達上限\n");return false;}// 檢查是否已訂閱for (int i = 0; i < publisher->subscriber_count; i++) {if (strcmp(publisher->subscribers[i]->name, subscriber_name) == 0) {printf("訂閱者 %s 已存在\n", subscriber_name);return false;}}// 創建新訂閱者Subscriber* subscriber = (Subscriber*)malloc(sizeof(Subscriber));strncpy(subscriber->name, subscriber_name, sizeof(subscriber->name) - 1);subscriber->callback = callback;subscriber->user_data = user_data;// 添加到訂閱者列表publisher->subscribers[publisher->subscriber_count++] = subscriber;printf("訂閱者 %s 已添加\n", subscriber_name);return true;
}bool unsubscribe(Publisher* publisher, const char* subscriber_name) {if (!publisher || !subscriber_name) return false;for (int i = 0; i < publisher->subscriber_count; i++) {if (strcmp(publisher->subscribers[i]->name, subscriber_name) == 0) {// 釋放訂閱者free(publisher->subscribers[i]);// 移動后續訂閱者for (int j = i; j < publisher->subscriber_count - 1; j++) {publisher->subscribers[j] = publisher->subscribers[j + 1];}publisher->subscriber_count--;printf("訂閱者 %s 已移除\n", subscriber_name);return true;}}printf("未找到訂閱者 %s\n", subscriber_name);return false;
}void publish(Publisher* publisher, const Topic* topic) {if (!publisher || !topic) return;printf("\n發布者 %s 發布主題 %s\n", publisher->name, topic->name);// 通知所有訂閱者for (int i = 0; i < publisher->subscriber_count; i++) {Subscriber* subscriber = publisher->subscribers[i];printf("通知訂閱者 %s\n", subscriber->name);subscriber->callback(topic, subscriber->user_data);}
}

4.4 使用示例 (main.c)

#include "pubsub.h"
#include <stdio.h>// 溫度傳感器訂閱者回調
void temperature_callback(const Topic* topic, void* user_data) {float* threshold = (float*)user_data;float temperature = *(float*)topic->data;printf("溫度傳感器收到數據: %.1f°C\n", temperature);if (temperature > *threshold) {printf("警告：溫度超過閾值 %.1f°C!\n", *threshold);}
}// 日志記錄訂閱者回調
void logger_callback(const Topic* topic, void* user_data) {printf("日志記錄器：主題 %s, 數據大小 %d, 時間戳 %d\n",topic->name, topic->data_size, topic->timestamp);
}int main() {// 創建發布者Publisher* sensor_publisher = create_publisher("傳感器發布者");// 創建溫度閾值float temp_threshold = 30.0f;// 訂閱主題subscribe(sensor_publisher, "溫度監控器", temperature_callback, &temp_threshold);subscribe(sensor_publisher, "系統日志", logger_callback, NULL);// 創建并發布溫度數據float temp_data[] = {25.5f, 28.3f, 32.7f};for (int i = 0; i < 3; i++) {Topic topic = {.name = "temperature",.data = &temp_data[i],.data_size = sizeof(float),.timestamp = (uint32_t)time(NULL)};publish(sensor_publisher, &topic);}// 取消訂閱unsubscribe(sensor_publisher, "系統日志");// 再次發布數據float final_temp = 35.2f;Topic topic = {.name = "temperature",.data = &final_temp,.data_size = sizeof(float),.timestamp = (uint32_t)time(NULL)};publish(sensor_publisher, &topic);// 清理資源destroy_publisher(sensor_publisher);return 0;
}

5. 代碼分析

5.1 關鍵設計點

1. 發布者管理訂閱者列表
2. 回調機制實現通知
3. 主題數據封裝
4. 動態訂閱管理

5.2 實現特點

1. 函數指針實現回調
2. 支持用戶數據傳遞
3. 訂閱者管理完善
4. 資源管理安全

6. 編譯和運行

gcc -c pubsub.c -o pubsub.o
gcc -c main.c -o main.o
gcc pubsub.o main.o -o pubsub_demo

7. 注意事項

1. 訂閱者數量限制
2. 內存管理安全
3. 回調函數異常處理
4. 線程安全考慮

8. 改進建議

1. 添加主題過濾
2. 實現異步通知
3. 支持優先級訂閱
4. 添加訂閱者分組

9. 總結

發布訂閱模式通過解耦發布者和訂閱者，實現了靈活的消息通知機制。這種模式特別適合處理事件驅動的場景。

參考資料

1. 《設計模式：可復用面向對象軟件的基礎》
2. 《C語言程序設計》
3. 《事件驅動編程》