linux socket多线程通信

基础概念

Linux Socket多线程通信是指在Linux操作系统下，通过Socket进行网络通信，并利用多线程技术实现并发处理的一种方式。Socket是网络通信的基本构建块，它允许不同计算机上的应用程序通过网络进行数据交换。多线程则允许多个任务在同一进程中并行执行，从而提高程序的响应速度和资源利用率。

类型

TCP Socket：面向连接的通信方式，保证数据的可靠传输。
UDP Socket：无连接的通信方式，适用于对实时性要求高的应用。

应用场景

Web服务器：处理大量并发的HTTP请求。
聊天服务器：实现实时聊天功能。
文件传输服务：支持多用户同时上传和下载文件。

常见问题及解决方法

问题1：线程安全问题

原因：多个线程同时访问和修改共享资源可能导致数据不一致或竞态条件。

解决方法：

使用互斥锁（Mutex）保护共享资源。
使用线程安全的库函数。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 8080
#define MAX_CLIENTS 10

int client_sockets[MAX_CLIENTS];
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void* handle_client(void* arg) {
    int client_socket = *(int*)arg;
    char buffer[1024] = {0};
    read(client_socket, buffer, 1024);
    pthread_mutex_lock(&mutex);
    printf("Received message: %s\n", buffer);
    pthread_mutex_unlock(&mutex);
    send(client_socket, "Message received", 17, 0);
    close(client_socket);
    return NULL;
}

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int addrlen = sizeof(address);

    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

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

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

    if (listen(server_fd, MAX_CLIENTS) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    while (1) {
        if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
            perror("accept");
            exit(EXIT_FAILURE);
        }
        pthread_t thread_id;
        pthread_create(&thread_id, NULL, handle_client, (void*)&new_socket);
        pthread_detach(thread_id);
    }

    return 0;
}

问题2：资源耗尽

原因：创建过多线程可能导致系统资源耗尽。

解决方法：

限制最大线程数。
使用线程池管理线程。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define PORT 8080
#define MAX_CLIENTS 10
#define MAX_THREADS 5

typedef struct {
    int client_socket;
    struct sockaddr_in address;
} ClientInfo;

ClientInfo clients[MAX_CLIENTS];
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int thread_count = 0;

void* handle_client(void* arg) {
    ClientInfo* client_info = (ClientInfo*)arg;
    int client_socket = client_info->client_socket;
    char buffer[1024] = {0};
    read(client_socket, buffer, 1024);
    pthread_mutex_lock(&mutex);
    printf("Received message: %s\n", buffer);
    pthread_mutex_unlock(&mutex);
    send(client_socket, "Message received", 17, 0);
    close(client_socket);
    free(client_info);
    return NULL;
}

int main() {
    int server_fd, new_socket;
    struct sockaddr_in address;
    int addrlen = sizeof(address);

    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

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

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

    if (listen(server_fd, MAX_CLIENTS) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    while (1) {
        if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
            perror("accept");
            exit(EXIT_FAILURE);
        }
        if (thread_count >= MAX_THREADS) {
            printf("Too many clients, waiting for a thread to free up...\n");
            sleep(1);
            continue;
        }
        ClientInfo* client_info = (ClientInfo*)malloc(sizeof(ClientInfo));
        client_info->client_socket = new_socket;
        memcpy(&client_info->address, &address, sizeof(address));
        pthread_t thread_id;
        pthread_create(&thread_id, NULL, handle_client, (void*)client_info);
        pthread_detach(thread_id);
        thread_count++;
    }

    return 0;
}