面试题：C语言Linux网络编程中的多线程TCP服务器优化

设计思路

TCP 服务器基础：使用 socket 函数创建套接字，bind 函数绑定地址，listen 函数监听连接。
多线程处理：当有新的客户端连接时，创建新线程处理该客户端的通信，这样可以实现并发处理多个客户端连接。
线程池优化：为了避免频繁创建和销毁线程带来的开销，使用线程池。线程池初始化时创建一定数量的线程，将客户端连接请求放入任务队列，线程从任务队列中取出任务进行处理。
资源竞争处理：在访问共享资源（如任务队列）时，使用互斥锁（pthread_mutex_t）来保证同一时间只有一个线程能访问共享资源，避免资源竞争。同时，使用条件变量（pthread_cond_t）来通知线程有新任务到来。

关键代码片段

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define PORT 8080
#define MAX_CLIENTS 100
#define THREAD_POOL_SIZE 10

// 任务结构体
typedef struct {
    int client_socket;
    struct sockaddr_in client_addr;
} Task;

// 线程池结构体
typedef struct {
    Task tasks[MAX_CLIENTS];
    int head;
    int tail;
    int count;
    pthread_mutex_t mutex;
    pthread_cond_t cond;
    int stop;
} ThreadPool;

ThreadPool pool;

// 线程处理函数
void* handle_client(void* arg) {
    while (1) {
        Task task;
        pthread_mutex_lock(&pool.mutex);
        while (pool.count == 0 &&!pool.stop) {
            pthread_cond_wait(&pool.cond, &pool.mutex);
        }
        if (pool.stop && pool.count == 0) {
            pthread_mutex_unlock(&pool.mutex);
            pthread_exit(NULL);
        }
        task = pool.tasks[pool.head];
        pool.head = (pool.head + 1) % MAX_CLIENTS;
        pool.count--;
        pthread_mutex_unlock(&pool.mutex);

        // 处理客户端通信
        char buffer[1024] = {0};
        int valread = read(task.client_socket, buffer, 1024);
        printf("Message from client: %s\n", buffer);
        char* hello = "Hello from server";
        send(task.client_socket, hello, strlen(hello), 0);
        close(task.client_socket);
    }
    return NULL;
}

int main(int argc, char const *argv[]) {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);

    // 创建套接字
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // 设置套接字选项
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // 绑定地址
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // 监听连接
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    // 初始化线程池
    pool.head = 0;
    pool.tail = 0;
    pool.count = 0;
    pool.stop = 0;
    pthread_mutex_init(&pool.mutex, NULL);
    pthread_cond_init(&pool.cond, NULL);

    pthread_t threads[THREAD_POOL_SIZE];
    for (int i = 0; i < THREAD_POOL_SIZE; i++) {
        pthread_create(&threads[i], NULL, handle_client, NULL);
    }

    while (1) {
        // 接受新的客户端连接
        if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
            perror("accept");
            continue;
        }

        pthread_mutex_lock(&pool.mutex);
        while (pool.count == MAX_CLIENTS) {
            pthread_mutex_unlock(&pool.mutex);
            close(new_socket);
            new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen);
            if (new_socket < 0) {
                perror("accept");
                continue;
            }
            pthread_mutex_lock(&pool.mutex);
        }
        pool.tasks[pool.tail].client_socket = new_socket;
        pool.tasks[pool.tail].client_addr = address;
        pool.tail = (pool.tail + 1) % MAX_CLIENTS;
        pool.count++;
        pthread_cond_signal(&pool.cond);
        pthread_mutex_unlock(&pool.mutex);
    }

    // 清理资源
    pool.stop = 1;
    pthread_cond_broadcast(&pool.cond);
    for (int i = 0; i < THREAD_POOL_SIZE; i++) {
        pthread_join(threads[i], NULL);
    }
    pthread_mutex_destroy(&pool.mutex);
    pthread_cond_destroy(&pool.cond);
    close(server_fd);
    return 0;
}

面试题：C语言Linux网络编程中的多线程TCP服务器优化

知识考点

面试题答案

设计思路

关键代码片段