diff --git a/day4/echo2.c b/day4/echo2.c
new file mode 100644
index 0000000..00f7a9c
--- /dev/null
+++ b/day4/echo2.c
@@ -0,0 +1,112 @@
+// 线程实现并发tcp通信
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <fcntl.h>
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <pthread.h>
+
+// 定义结构体：用于描述连接的客户端信息
+typedef struct client_s
+{
+    unsigned char ip[INET_ADDRSTRLEN]; // 16
+    int fd;
+} Client;
+
+void *client_task(void *arg)
+{
+    Client *client = (Client *)arg;
+    while (1)
+    {
+        char buf[128] = "";
+        ssize_t len = recv(client->fd, buf, 128, 0);
+        if (len > 0)
+        {
+            int i = 0;
+            while (buf[i])
+            {
+                buf[i] = toupper(buf[i]);
+                i++;
+            }
+
+            send(client->fd, buf, len, 0);
+
+            if (strncmp(buf, "BYE", 3) == 0)
+            {
+                break;
+            }
+        }
+    }
+
+    close(client->fd);
+    // pthread_exit(NULL); // 结束线程
+    printf("%s 关闭连接\n", client->ip);
+
+    free(client); // 回收空间
+}
+
+int main(int argc, char const *argv[])
+{
+    // 1. 创建 socket
+    int sock_fd = socket(AF_INET, SOCK_STREAM, 0);
+    if (sock_fd < 0)
+    {
+        perror("socket");
+        return 1;
+    }
+
+    // 2. bind
+    struct sockaddr_in server_addr;
+    bzero(&server_addr, sizeof(server_addr));
+    server_addr.sin_family = AF_INET;
+    server_addr.sin_port = htons(atoi(argv[1]));
+    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
+
+    int flag = bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr));
+    if (flag != 0)
+    {
+        perror("bind");
+        close(sock_fd);
+        return 1;
+    }
+
+    // 3. 创建监听队列
+    listen(sock_fd, 100);
+
+    printf("-----ECHO 服务器已开启端口号为:%s-----\n", argv[1]);
+
+    // 4. 开始接收客户端的连接（并发接收多个客户端）
+    while (1)
+    {
+        struct sockaddr_in client_addr;
+        bzero(&client_addr, sizeof(client_addr));
+        socklen_t client_addr_len = sizeof(client_addr);
+
+        int client_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &client_addr_len);
+
+        char clinet_ip[INET_ADDRSTRLEN] = "";
+        inet_ntop(AF_INET, &client_addr.sin_addr.s_addr, clinet_ip, INET_ADDRSTRLEN);
+        printf("%s 连接成功\n", clinet_ip);
+
+        // 创建线程实现并发通信
+        Client *client = malloc(sizeof(Client)); // 创建堆空间
+        strcpy(client->ip, clinet_ip);
+        client->fd = client_fd;
+
+        pthread_t tid;
+        pthread_create(&tid, NULL, client_task, client);
+        pthread_detach(tid); // 分离线程
+        // pthread_join(tid,NULL);
+    }
+
+    // 主进程的范畴
+    close(sock_fd);
+
+    return 0;
+}