bool HasChanged { get; }
bool ActiveChangeCallbacks { get; }
IDisposable RegisterChangeCallback(Action<object?> callback, object? state);

static void Main(string[] args)
{
    CancellationTokenSource cs = new();
    // 这里获取token
    CancellationToken token = cs.Token;
    // token 可以注册回调
    token.Register(() =>
    {
        Console.WriteLine("你按下了【K】键");
    });
    // 启动一个新task
    Task myTask = Task.Run(() =>
    {
        // 等待输入，如果按下【K】键，就让CancellationTokenSource取消
        ConsoleKeyInfo keyInfo;
        while(true)
        {
            keyInfo = Console.ReadKey(true);
            if(keyInfo.Key == ConsoleKey.K)
            {
                // 取消
                cs.Cancel();
                break;
            }
        }
    });
    // 主线程等待任务完成
    Task.WaitAll(myTask);
}

CREATE TABLE [dbo].[tb_configdata](
    [ID] [int] NOT NULL,
    [config_key] [nvarchar](15) NOT NULL,
    [config_value] [nvarchar](30) NOT NULL,
    [remark] [nvarchar](50) NULL,
 CONSTRAINT [PK_tb_configdata] PRIMARY KEY CLUSTERED 
(
    [ID] ASC,
    [config_key] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO

// 实体类
public class MyConfigData
{
    public int ID { get; set; }
    public string ConfigKey { get; set; } = string.Empty;
    public string ConfigValue { get; set; } = string.Empty;
    public string? Remark { get; set; }
}
// 数据库上下文对象
public class DemoConfigDBContext : DbContext
{
    public DbSet<MyConfigData> ConfigData => Set<MyConfigData>();
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("Data Source=DEV-PC\\SQLTEST;Initial Catalog=Demo;Integrated Security=True;Connect Timeout=30;Encrypt=True;Trust Server Certificate=True;Application Intent=ReadWrite;Multi Subnet Failover=False");
    }
    protected override void OnModelCreating(ModelBuilder modelbd)
    {
        modelbd.Entity<MyConfigData>()
            .ToTable("tb_configdata")
            .HasKey(c => new { c.ID, c.ConfigKey });
        modelbd.Entity<MyConfigData>()
            .Property(c => c.ConfigKey)
            .HasColumnName("config_key");
        modelbd.Entity<MyConfigData>()
            .Property(c => c.ConfigValue)
            .HasColumnName("config_value");
        modelbd.Entity<MyConfigData>()
            .Property(c => c.Remark)
            .HasColumnName("remark");
    }
}

public class MyConfigurationProvider : ConfigurationProvider, IDisposable
{
    private System.Threading.Timer theTimer;
    public MyConfigurationProvider()
    {
        theTimer = new Timer(OnTimer, null, 100, 10000);
    }
    private void OnTimer(object? state)
    {
        // 先调用Load方法，然后用OnReload触发更新通知
        Load();
        OnReload();
    }
    public void Dispose()
    {
        theTimer?.Change(0, 0);
        theTimer?.Dispose();
    }
    public override void Load()
    {
        // 先读取一下
        using DemoConfigDBContext dbctx = new();
        // 如果无数据，先初始化
        if(dbctx.ConfigData.Count() == 0)
        {
            InitData(dbctx.ConfigData);
        }
        // 加载数据
        Data = dbctx.ConfigData.ToDictionary(k => k.ConfigKey, k => (string?)k.ConfigValue);
        // 本地函数
        void InitData(DbSet<MyConfigData> set)
        {
            int _id = 1;
            set.Add(new()
            {
                ID = _id,
                ConfigKey = "page_size",
                ConfigValue = "25"
            });
            _id += 1;
            set.Add(new()
            {
                ID = _id,
                ConfigKey = "format",
                ConfigValue = "xml"
            });
            _id += 1;
            set.Add(new()
            {
                ID = _id,
                ConfigKey = "limited_height",
                ConfigValue = "1450"
            });
            _id += 1;
            set.Add(new()
            {
                ID = _id,
                ConfigKey = "msg_lead",
                ConfigValue = "TDXA_"
            });
            // 保存数据
            dbctx.SaveChanges();
        }
    }
}

public class MyConfigurationSource : IConfigurationSource
{
    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new MyConfigurationProvider();
    }
}

var builder = WebApplication.CreateBuilder(args);
// 清空配置源
builder.Configuration.Sources.Clear();
// 添加配置源到Sources
builder.Configuration.Sources.Add(new MyConfigurationSource());
var app = builder.Build();

app.MapGet("/", (IConfiguration config) =>
{
    StringBuilder bd = new();
    foreach(var kp in config.AsEnumerable())
    {
        bd.AppendLine($"{kp.Key} = {kp.Value}");
    }
    return bd.ToString();
});

update tb_configdata
    set config_value = N'55'
    where config_key = N'page_size'
 
update tb_configdata
    set config_value = N'1900'
    where config_key = N'limited_height'

public class MyConfigurationSource : IConfigurationSource
{
    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        // 此处可以临时build一个配置树，就能获取到JSON配置文件里面的连接字符串了
        var config = builder.Build();
        string connStr = config["ConnectionStrings:test"]!;
        return new MyConfigurationProvider(connStr);
    }
}

public class MyConfigurationProvider : ConfigurationProvider, IDisposable
{
    private System.Threading.Timer theTimer;
    private string connectString;
    public MyConfigurationProvider(string cnnstr)
    {
        connectString = cnnstr;
        ……
    }
    ……
}

public class DemoConfigDBContext : DbContext
{
    private string connStr;
    public DemoConfigDBContext(string connectionString)
    {
        connStr = connectionString;
    }
    ……
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(connStr);
    }
}

{
  "Logging": {
    ……
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "test": "Data Source=DEV-PC\\SQLTEST;Initial Catalog=Demo;Integrated Security=True;Connect Timeout=30;Encrypt=True;Trust Server Certificate=True;Application Intent=ReadWrite;Multi Subnet Failover=False"
  }
}

var builder = WebApplication.CreateBuilder(args);
// 清空配置源
builder.Configuration.Sources.Clear();
// 添加配置源到Sources
builder.Configuration.AddJsonFile("appsettings.json");
builder.Configuration.Sources.Add(new MyConfigurationSource());
var app = builder.Build();

internal class TestForm : Form
{
    private IDisposable _changeTokenReg;
    private TextBox _txtMsg;
    public TestForm(Func<IChangeToken?> getToken)
    {
        // 初始化子级控件
        _txtMsg = new()
        {
            Dock = DockStyle.Fill,
            Margin = new Padding(5),
            Multiline = true,
            ScrollBars = ScrollBars.Vertical
        };
        Controls.Add(_txtMsg);
        _changeTokenReg = ChangeToken.OnChange(getToken, OnCallback);
    }
    // 回调方法
    void OnCallback()
    {
        DateTime curtime = DateTime.Now;
        string str = $"{curtime.ToLongTimeString()} 新年快乐\r\n";
        _txtMsg.BeginInvoke(() =>
        {
            _txtMsg.AppendText(str);
        });
    }
    protected override void Dispose(bool disposing)
    {
        // 释放对象
        if (disposing)
        {
            _changeTokenReg?.Dispose();
        }
        base.Dispose(disposing);
    }
}

// 咱们示例中用的是这个版本
static IDisposable OnChange(Func<IChangeToken?> changeTokenProducer, Action changeTokenConsumer);
// 这是另一个重载
static IDisposable OnChange<TState>(Func<IChangeToken?> changeTokenProducer, Action<TState> changeTokenConsumer, TState state);

 public static IDisposable OnChange<TState>(Func<IChangeToken?> changeTokenProducer, Action<TState> changeTokenConsumer, TState state)
 {
     if (changeTokenProducer is null)
     {
         ThrowHelper.ThrowArgumentNullException(ExceptionArgument.changeTokenProducer);
     }
     if (changeTokenConsumer is null)
     {
         ThrowHelper.ThrowArgumentNullException(ExceptionArgument.changeTokenConsumer);
     }
     return new ChangeTokenRegistration<TState>(changeTokenProducer, changeTokenConsumer, state);
 }

private void OnChangeTokenFired()
{
    // The order here is important. We need to take the token and then apply our changes BEFORE
    // registering. This prevents us from possible having two change updates to process concurrently.
    //
    // If the token changes after we take the token, then we'll process the update immediately upon
    // registering the callback.
    IChangeToken? token = _changeTokenProducer();
    try
    {
        _changeTokenConsumer(_state);
    }
    finally
    {
        // We always want to ensure the callback is registered
        RegisterChangeTokenCallback(token);
    }
}
private void RegisterChangeTokenCallback(IChangeToken? token)
{
    if (token is null)
    {
        return;
    }
    IDisposable registraton = token.RegisterChangeCallback(s => ((ChangeTokenRegistration<TState>?)s)!.OnChangeTokenFired(), this);
    if (token.HasChanged && token.ActiveChangeCallbacks)
    {
        registraton?.Dispose();
        return;
    }
    SetDisposable(registraton);
}

public partial class Form1 : Form
{
    private CancellationTokenSource _cancelTkSource;
    private CancellationChangeToken _changeToken;
    public Form1()
    {
        InitializeComponent();
        _cancelTkSource = new CancellationTokenSource();
        _changeToken = new(_cancelTkSource.Token);
        button1.Click += OnButton1Click;
        button2.Click += OnButton2Click;
    }
    private void OnButton2Click(object? sender, EventArgs e)
    {
        for(int t= 0; t < 5; t++)
        {
            TestForm frm = new(GetChangeToken);
            frm.Text = "窗口" + (t + 1);
            frm.Size = new Size(300, 240);
            frm.StartPosition = FormStartPosition.CenterParent;
            frm.Show(this);
        }
    }
    // 这个地方就是触发token了，所以要先换上新的实例
    private void OnButton1Click(object? sender, EventArgs e)
    {
        // 先创建新的实例
        var oldsource = Interlocked.Exchange(ref _cancelTkSource, new CancellationTokenSource());
        Interlocked.Exchange(ref _changeToken, new CancellationChangeToken(_cancelTkSource.Token));
        // 只要CancellationTokenSource一取消，其他客户端会收到通知
        oldsource.Cancel();
    }
    // 这个方法传递给 TestForm 构造函数，再传给 OnChange 静态方法
    public IChangeToken? GetChangeToken()
    {
        return _changeToken;
    }
}