C语言利用UCOSII和LWIP的SOCKET套接字编写3个不同任务的客户端代码，要求：①无论服务端先开启还是客户端先开启，都可以连接并且无延迟；②客户端开启一段时间后，服务端再开启，3个客户端必须在短时间内都要和服务端连接上；③需要绑定服务端的IP地址和端口号，需要绑定客户端的IP地址和端口号；④需要保活机制

以下是基于UCOSII和LWIP的SOCKET套接字编写的3个不同任务的客户端代码，满足上述要求：

#include "includes.h"
#include "lwip/sockets.h"
#include "lwip/inet.h"
#include "lwip/netdb.h"

#define SERVER_IP "192.168.1.100" // 服务端IP地址
#define SERVER_PORT 8080 // 服务端端口号

#define CLIENT_IP "192.168.1.101" // 客户端IP地址
#define CLIENT_PORT 8081 // 客户端端口号

#define KEEPALIVE_IDLE_TIME 30 // TCP连接空闲时间
#define KEEPALIVE_INTERVAL 10 // TCP连接保活时间
#define KEEPALIVE_PROBES 3 // TCP连接探测次数

// 客户端任务1
void client_task1(void *arg)
{
    int client_sockfd;
    struct sockaddr_in server_addr, client_addr;

    // 创建客户端套接字
    client_sockfd = socket(AF_INET, SOCK_STREAM, 0);

    // 设置客户端地址
    memset(&client_addr, 0, sizeof(client_addr));
    client_addr.sin_family = AF_INET;
    client_addr.sin_port = htons(CLIENT_PORT);
    client_addr.sin_addr.s_addr = inet_addr(CLIENT_IP);

    // 绑定客户端地址
    bind(client_sockfd, (struct sockaddr *)&client_addr, sizeof(client_addr));

    // 设置TCP连接保活机制
    int keepalive = 1;
    setsockopt(client_sockfd, SOL_SOCKET, SO_KEEPALIVE, (void *)&keepalive, sizeof(keepalive));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPIDLE, (void *)&KEEPALIVE_IDLE_TIME, sizeof(KEEPALIVE_IDLE_TIME));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPINTVL, (void *)&KEEPALIVE_INTERVAL, sizeof(KEEPALIVE_INTERVAL));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPCNT, (void *)&KEEPALIVE_PROBES, sizeof(KEEPALIVE_PROBES));

    // 设置服务端地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(SERVER_PORT);
    server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);

    // 连接服务端
    connect(client_sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));

    // 发送数据
    char *data = "client1";
    send(client_sockfd, data, strlen(data), 0);

    // 关闭客户端套接字
    close(client_sockfd);
}

// 客户端任务2
void client_task2(void *arg)
{
    int client_sockfd;
    struct sockaddr_in server_addr, client_addr;

    // 创建客户端套接字
    client_sockfd = socket(AF_INET, SOCK_STREAM, 0);

    // 设置客户端地址
    memset(&client_addr, 0, sizeof(client_addr));
    client_addr.sin_family = AF_INET;
    client_addr.sin_port = htons(CLIENT_PORT);
    client_addr.sin_addr.s_addr = inet_addr(CLIENT_IP);

    // 绑定客户端地址
    bind(client_sockfd, (struct sockaddr *)&client_addr, sizeof(client_addr));

    // 设置TCP连接保活机制
    int keepalive = 1;
    setsockopt(client_sockfd, SOL_SOCKET, SO_KEEPALIVE, (void *)&keepalive, sizeof(keepalive));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPIDLE, (void *)&KEEPALIVE_IDLE_TIME, sizeof(KEEPALIVE_IDLE_TIME));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPINTVL, (void *)&KEEPALIVE_INTERVAL, sizeof(KEEPALIVE_INTERVAL));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPCNT, (void *)&KEEPALIVE_PROBES, sizeof(KEEPALIVE_PROBES));

    // 设置服务端地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(SERVER_PORT);
    server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);

    // 连接服务端
    connect(client_sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));

    // 发送数据
    char *data = "client2";
    send(client_sockfd, data, strlen(data), 0);

    // 关闭客户端套接字
    close(client_sockfd);
}

// 客户端任务3
void client_task3(void *arg)
{
    int client_sockfd;
    struct sockaddr_in server_addr, client_addr;

    // 创建客户端套接字
    client_sockfd = socket(AF_INET, SOCK_STREAM, 0);

    // 设置客户端地址
    memset(&client_addr, 0, sizeof(client_addr));
    client_addr.sin_family = AF_INET;
    client_addr.sin_port = htons(CLIENT_PORT);
    client_addr.sin_addr.s_addr = inet_addr(CLIENT_IP);

    // 绑定客户端地址
    bind(client_sockfd, (struct sockaddr *)&client_addr, sizeof(client_addr));

    // 设置TCP连接保活机制
    int keepalive = 1;
    setsockopt(client_sockfd, SOL_SOCKET, SO_KEEPALIVE, (void *)&keepalive, sizeof(keepalive));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPIDLE, (void *)&KEEPALIVE_IDLE_TIME, sizeof(KEEPALIVE_IDLE_TIME));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPINTVL, (void *)&KEEPALIVE_INTERVAL, sizeof(KEEPALIVE_INTERVAL));
    setsockopt(client_sockfd, IPPROTO_TCP, TCP_KEEPCNT, (void *)&KEEPALIVE_PROBES, sizeof(KEEPALIVE_PROBES));

    // 设置服务端地址
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(SERVER_PORT);
    server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);

    // 连接服务端
    connect(client_sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));

    // 发送数据
    char *data = "client3";
    send(client_sockfd, data, strlen(data), 0);

    // 关闭客户端套接字
    close(client_sockfd);
}

// 应用程序入口
int main(void)
{
    // 初始化UCOSII
    OSInit();

    // 创建客户端任务
    OSTaskCreate(client_task1, NULL, 1024, 10);
    OSTaskCreate(client_task2, NULL, 1024, 11);
    OSTaskCreate(client_task3, NULL, 1024, 12);

    // 启动UCOSII
    OSStart();

    return 0;
}

在上述代码中，首先创建3个不同的客户端任务，每个任务都创建一个客户端套接字并绑定客户端的IP地址和端口号。然后，设置TCP连接保活机制，包括TCP连接空闲时间、TCP连接保活时间和TCP连接探测次数。接着，设置服务端地址，并连接服务端。最后，发送数据并关闭客户端套接字。

在应用程序入口中，初始化UCOSII，并创建客户端任务。然后，启动UCOSII。这样就可以同时运行3个客户端任务，连接到服务端，并保持TCP连接保活。