c-ares多通道/线程反向查找

c-ares 是一个用于异步域名解析的 C 库。其中的反向查找可以通过多通道/ 线程的方式来实现，具体方法如下所示：

1. 初始化 c-ares ares_library_init(ARES_LIB_INIT_ALL);

2. 创建 c-ares 上下文 ares_channel channels[NUM_THREADS]; ares_channel_init(channels);

3. 设置回调函数 ares_callback(callback, data);

4. 添加反向 IP 查询 ares_getnameinfo(channels[thread_id], sa, sa_len, ARES_NI_NUMERICSERV, callback, data);

5. 启动 c-ares ares_process_fd(channels[thread_id], ARES_SOCKET_BAD, ARES_SOCKET_BAD);

6. 关闭 c-ares ares_destroy(channels[thread_id]); ares_library_cleanup();

完整代码示例如下所示：

#include <stdio.h> #include <stdlib.h> #include <arpa/inet.h> #include <ares.h> #include <netdb.h> #include <sys/socket.h> #include <netinet/in.h>

#define NUM_THREADS 4

struct thread_data { int thread_id; struct sockaddr_in sa; socklen_t sa_len; };

void callback(void *arg, int status, int timeouts, struct hostent *hostent) { struct thread_data *data = (struct thread_data *)arg;

if(status == ARES_SUCCESS && hostent) {
    printf("Thread %d: Host %s\n", data->thread_id, hostent->h_name);
} else {
    printf("Thread %d: ERROR\n", data->thread_id);
}

}

void* thread_func(void *arg) { struct thread_data *data = (struct thread_data *)arg;

// 1. 初始化 c-ares
ares_library_init(ARES_LIB_INIT_ALL);

// 2. 创建 c-ares 上下文
ares_channel channels[NUM_THREADS];
ares_channel_init(channels);

// 3. 设置回调函数
ares_callback(callback, data);

// 4. 添加反向 IP 查询
ares_getnameinfo(channels[data->thread_id], (struct sockaddr *)&data->sa