diff --git a/homework.cs b/homework.cs
index 91a7fc0..a91fb7e 100644
--- a/homework.cs
+++ b/homework.cs
@@ -29,7 +29,30 @@ public Task<List<Book>> GetBooksAsync()
     public async Task UpdateInventoryAsync(string title, int quantity)
     {
         await Task.Delay(100); // 模拟网络延迟
-
+        lock (_lock)
+        {
+            bool flag_bookfound = false;
+            foreach (var item in _books)
+            {
+                if (item.Title == title)
+                {
+                    flag_bookfound = true;
+                    if (item.Inventory >= quantity)
+                    {
+                        item.Inventory -= quantity;
+                        Console.WriteLine($"成功购买{title}: {quantity}本");
+                    }
+                    else
+                    {
+                        Console.WriteLine($"{title}目前仅有{item.Inventory}本，库存不足");
+                    }
+                }
+            }
+            if (!flag_bookfound)
+            {
+                Console.WriteLine($"未找到书籍：{title}");
+            }
+        }
         // TODO: 使用 lock 语句保证线程安全
         // 提示：在 lock 块中查找书籍并更新库存，若库存不足则输出提示
     }
@@ -42,6 +65,7 @@ public class BookStore
     // TODO: 实现异步购书方法CheckoutAsync，调用 UpdateInventoryAsync
     public async Task CheckoutAsync(string bookTitle, int quantity)
     {
+        await _db.UpdateInventoryAsync(bookTitle, quantity);
     }
 
     public async Task SimulateMultipleUsers()
@@ -59,9 +83,15 @@ public async Task SimulateMultipleUsers()
         // 提示：创建多个 Task 调用 CheckoutAsync，并传入不同书名和数量
         var tasks = new List<Task>
         {
-            
+            CheckoutAsync("C#入门", 2),
+            CheckoutAsync("C#入门", 3),
+            CheckoutAsync("异步编程", 1),
+            CheckoutAsync("异步编程", 2),
+            CheckoutAsync("异步编程", 3),
         };
 
+        await Task.WhenAll(tasks);
+
 
         Console.WriteLine("\n购买后库存：");
         books = await _db.GetBooksAsync();