Async-and-Multi_thread-赵景言-笃实45

Program.cs

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+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+public class Book
+{
+    public string Title { get; set; }
+    public decimal Price { get; set; }
+    public int Inventory { get; set; }
+}
+
+public class Database
+{
+    private readonly List<Book> _books = new List<Book>();
+    private readonly object _lock = new object();
+
+    public Database()
+    {
+        _books.Add(new Book { Title = "C#入门", Price = 39.9m, Inventory = 10 });
+        _books.Add(new Book { Title = "异步编程", Price = 59.9m, Inventory = 5 });
+    }
+
+    public Task<List<Book>> GetBooksAsync()
+    {
+        return Task.FromResult(_books);
+    }
+
+    public async Task UpdateInventoryAsync(string title, int quantity)
+    {
+        await Task.Delay(100); // 模拟网络延迟
+        Console.WriteLine($"正在更新库存：{title}，数量：{quantity}");
+        // TODO: 使用 lock 语句保证线程安全
+        // 提示：在 lock 块中查找书籍并更新库存，若库存不足则输出提示
+        lock (_lock)
+        {
+            var book = _books.Find(b => b.Title == title);
+            if (book != null)
+            {
+                if (book.Inventory >= quantity)
+                {
+                    book.Inventory -= quantity;
+                    Console.WriteLine($"成功购买 {quantity} 本《{book.Title}》，剩余库存：{book.Inventory}");
+                }
+                else
+                {
+                    Console.WriteLine($"库存不足，无法购买 {quantity} 本《{book.Title}》，当前库存：{book.Inventory}");
+                }
+            }
+            else
+            {
+                Console.WriteLine($"未找到书籍《{title}》");
+            }
+        }
+    }
+}
+
+public class BookStore
+{
+    private readonly Database _db = new Database();
+
+    // TODO: 实现异步购书方法CheckoutAsync，调用 UpdateInventoryAsync
+    public async Task CheckoutAsync(string bookTitle, int quantity)
+    {
+        Console.WriteLine($"尝试购买 {quantity} 本《{bookTitle}》...");
+        await _db.UpdateInventoryAsync(bookTitle, quantity);
+        Console.WriteLine($"完成购买 {quantity} 本《{bookTitle}》\n");
+    }
+
+    public async Task SimulateMultipleUsers()
+    {
+        var books = await _db.GetBooksAsync();
+        Console.WriteLine("当前书店库存：");
+        foreach (var book in books)
+        {
+            Console.WriteLine($"- {book.Title}：{book.Inventory} 本");
+        }
+
+        Console.WriteLine("\n 开始模拟多用户购书...\n");
+
+        // TODO: 使用 Task.WhenAll 模拟多个用户并发购书
+        // 提示：创建多个 Task 调用 CheckoutAsync，并传入不同书名和数量
+        var tasks = new List<Task>
+        {
+            CheckoutAsync("C#入门", 2),
+            CheckoutAsync("C#入门", 3),
+            CheckoutAsync("异步编程", 1),
+            CheckoutAsync("异步编程", 2),
+            CheckoutAsync("异步编程", 3)
+        };
+
+        await Task.WhenAll(tasks);
+        Console.WriteLine("\n所有购书操作已完成。\n");
+
+        // 输出最终库存
+        books = await _db.GetBooksAsync();
+        Console.WriteLine("最终库存：");
+        foreach (var book in books)
+        {
+            Console.WriteLine($"- {book.Title}：{book.Inventory} 本");
+        }
+        ;
+
+
+        Console.WriteLine("\n购买后库存：");
+        books = await _db.GetBooksAsync();
+        foreach (var book in books)
+        {
+            Console.WriteLine($"- {book.Title}：{book.Inventory} 本");
+        }
+    }
+}
+
+public class Program
+{
+    public static async Task Main()
+    {
+        var store = new BookStore();
+        await store.SimulateMultipleUsers();
+    }
+}