diff --git a/main.cpp b/main.cpp
index f4ecab8..708799f 100644
--- a/main.cpp
+++ b/main.cpp
@@ -6,6 +6,10 @@
 #include <string>
 #include <thread>
 #include <map>
+#include <chrono>
+#include <shared_mutex>
+#include <mutex>
+#include <future>
 
 
 struct User {
@@ -15,11 +19,18 @@ struct User {
 };
 
 std::map<std::string, User> users;
-std::map<std::string, long> has_login;  // 换成 std::chrono::seconds 之类的
+// std::map<std::string, long> has_login;  // 换成 std::chrono::seconds 之类的
+
+std::map<std::string, std::chrono::steady_clock::time_point> has_login;
+std::shared_mutex user_mutex;
+std::shared_mutex login_mutex;
+
+
 
 // 作业要求1：把这些函数变成多线程安全的
 // 提示：能正确利用 shared_mutex 加分，用 lock_guard 系列加分
 std::string do_register(std::string username, std::string password, std::string school, std::string phone) {
+    std::unique_lock lock(user_mutex);
     User user = {password, school, phone};
     if (users.emplace(username, user).second)
         return "注册成功";
@@ -27,15 +38,28 @@ std::string do_register(std::string username, std::string password, std::string
         return "用户名已被注册";
 }
 
+using double_ms = std::chrono::duration<double, std::milli>;
 std::string do_login(std::string username, std::string password) {
     // 作业要求2：把这个登录计时器改成基于 chrono 的
-    long now = time(NULL);   // C 语言当前时间
-    if (has_login.find(username) != has_login.end()) {
-        int sec = now - has_login.at(username);  // C 语言算时间差
-        return std::to_string(sec) + "秒内登录过";
+    
+   
+    {   
+        std::unique_lock lock(login_mutex); // ensure has_login[username] = t1 without data race
+        auto t1 = std::chrono::steady_clock::now();
+        if (has_login.find(username) != has_login.end()) {
+            auto diff = t1 - has_login[username];
+            double msec = std::chrono::duration_cast<double_ms>(diff).count();
+            return std::to_string(msec) + "ms内登录过";
+        }
+        has_login[username] = t1;
     }
-    has_login[username] = now;
-
+    // has_login[username] = now;
+    // {  
+    //     std::unique_lock lock(login_mutex);
+        
+    // }
+    
+    std::shared_lock lock(user_mutex); // shared_lock确保.find的时候没有write
     if (users.find(username) == users.end())
         return "用户名错误";
     if (users.at(username).password != password)
@@ -44,6 +68,8 @@ std::string do_login(std::string username, std::string password) {
 }
 
 std::string do_queryuser(std::string username) {
+    std::shared_lock lock(user_mutex);
+     if (users.find(username) == users.end()) return "user name does not exist";
     auto &user = users.at(username);
     std::stringstream ss;
     ss << "用户名: " << username << std::endl;
@@ -54,13 +80,41 @@ std::string do_queryuser(std::string username) {
 
 
 struct ThreadPool {
+    std::vector<std::future<void>> futures;
     void create(std::function<void()> start) {
         // 作业要求3：如何让这个线程保持在后台执行不要退出？
         // 提示：改成 async 和 future 且用法正确也可以加分
-        std::thread thr(start);
+        // not sure if to std::launch::aynsc here, too many threads might get it stuck
+        // std::async(function<void()>) will return a future element
+        futures.emplace_back(std::async(start));
+    }
+    void waitForAll() {
+        for (auto &f : futures) {
+            f.get(); // wait for all to happen
+        }
     }
 };
 
+// 下面这样写应该也可以，
+// struct ThreadPool {
+//     // 动态管理vector大小，自动destruct
+//     std::unique_ptr<std::vector<std::thread>> threads;
+
+//     ThreadPool() : threads(std::make_unique<std::vector<std::thread>>()) {}
+
+//     void create(std::function<void()> start) {
+//         threads->emplace_back(std::thread(start));
+//     }
+
+//     void waitForAll() {
+//         for (auto &t : *threads) {
+//             if (t.joinable()) {
+//                 t.join();  // 等待所有线程完成
+//             }
+//         }
+//     }
+// };
+
 ThreadPool tpool;
 
 
@@ -73,17 +127,23 @@ std::string phone[] = {"110", "119", "120", "12315"};
 
 int main() {
     for (int i = 0; i < 262144; i++) {
+        // call register
         tpool.create([&] {
             std::cout << do_register(test::username[rand() % 4], test::password[rand() % 4], test::school[rand() % 4], test::phone[rand() % 4]) << std::endl;
         });
+        
+        // call login
         tpool.create([&] {
             std::cout << do_login(test::username[rand() % 4], test::password[rand() % 4]) << std::endl;
         });
+        
+        // user might be queried to wait
         tpool.create([&] {
             std::cout << do_queryuser(test::username[rand() % 4]) << std::endl;
         });
     }
 
     // 作业要求4：等待 tpool 中所有线程都结束后再退出
+    tpool.waitForAll();
     return 0;
-}
+}
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