我们可以进一步使用 consul 的变更通知。它只是通过添加一个参数(最后一个索引配置的值)来工作的，HTTP 请求会一直阻塞，直到下一次配置变更(或 HttpClient 超时)。

与前面的类相比，我们只需添加一个方法 ListenToConfigurationChanges，以便在后台监听 consul 的阻塞 HTTP 。

public class ConsulConfigurationProvider : ConfigurationProvider
{
    private const string ConsulIndexHeader = "X-Consul-Index";

    private readonly string _path;
    private readonly HttpClient _httpClient;
    private readonly IReadOnlyList<Uri> _consulUrls;
    private readonly Task _configurationListeningTask;
    private int _consulUrlIndex;
    private int _failureCount;
    private int _consulConfigurationIndex;

    public ConsulConfigurationProvider(IEnumerable<Uri> consulUrls, string path)
    {
        _path = path;
        _consulUrls = consulUrls.Select(u => new Uri(u, $"v1/kv/{path}")).ToList();

        if (_consulUrls.Count <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(consulUrls));
        }

        _httpClient = new HttpClient(new HttpClientHandler { AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip }, true);
        _configurationListeningTask = new Task(ListenToConfigurationChanges);
    }

    public override void Load() => LoadAsync().ConfigureAwait(false).GetAwaiter().GetResult();

    private async Task LoadAsync()
    {
        Data = await ExecuteQueryAsync();

        if (_configurationListeningTask.Status == TaskStatus.Created)
            _configurationListeningTask.Start();
    }

    private async void ListenToConfigurationChanges()
    {
        while (true)
        {
            try
            {
                if (_failureCount > _consulUrls.Count)
                {
                    _failureCount = 0;
                    await Task.Delay(TimeSpan.FromMinutes(1));
                }