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How to await on a message subscribed from Redis?

I have the following code structure:

private AutoResetEvent _renderCompleteEvent = new AutoResetEvent(false);

// GET: api/<controller>
[HttpGet]
public async Task<string> GetAsync()
{
    // Subscribe to the response from Redis publish
    _pubsub.Subscribe("x", (channel, message) => RenderComplete(message));

    // Ideally I would like to wait on RenderComplete and have it return a string here
    // string messageContent = await RenderComplete()..

    _renderCompleteEvent.WaitOne();

    return messageContent;
}

private void RenderComplete(string json)
{
    _renderCompleteEvent.Set();
}

Ideally I would like to be able to wait on a function call which would return when I get a message from Redis and the function would return the message content.

Instead I had to implement it using an AutoResetEvent and I would have to pass the message content back as a global class variable.

Is there a way to achieve what I want here to make the code a bit more elegant?

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2

Answers


  1. 0

    Yes, you can use a TaskCompletionSource<T> to make pretty much anything awaitable:

    private TaskCompletionSource<string> _tcs = new TaskCompletionSource<string>();

// GET: api/<controller>
[HttpGet]
public async Task<string> GetAsync()
{
  // Subscribe to the response from Redis publish
  _pubsub.Subscribe("x", (channel, message) => RenderComplete(message));

  string messageContent = _tcs.Task;

  return messageContent;
}

private void RenderComplete(string json)
{
  _tcs.TrySetResult(json);
}

    Note that TaskCompletionSource<T> can only be completed once; it can’t be “reset”. So you would probably prefer a solution like this that combines the subscribing and message retrieval:

    // GET: api/<controller>
[HttpGet]
public async Task<string> GetAsync()
{
  string messageContent = await GetMessageAsync();

  return messageContent;
}

private Task<string> GetMessageAsync()
{
  var tcs = new TaskCompletionSource<string>();
  _pubsub.Subscribe("x", (channel, message) => tcs.TrySetResult(message));
  return tcs.Task;
}

    You may also want to modify GetMessageAsync to handle things like unsubscribing and timing out if there’s no message.

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  2. 0

    i did it and founded this solution to call minio async service in asp.netcore.

    your Service in controller

        [HttpGet]
    [Route("/api/getFileList")]
    public async Task<Object> getFileList()
    {
        var endpoint = "127.0.0.1";
        int port = 9000;
        var accessKey = "your accessKey ";
        var secretKey = "your secretKey";

        try
        {
            var minio = new MinioClient()
                                .WithEndpoint(endpoint, port)
                                .WithCredentials(accessKey, secretKey)
                                //.WithSSL()
                                .Build();

            var listFile = await getListFileName(minio);

            if (listFile != null)
                return listFile;
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
        return "";
    }

    get file list from minio service

        private TaskCompletionSource<List<string>> _tcs = new TaskCompletionSource<List<string>>();


    [Obsolete]
    private async Task<List<string>> getListFile(MinioClient minio)
    {

        var bucketName = "test";
        List<string> bucketKeys = new List<string>();

        IObservable<Item> observable = minio.ListObjectsAsync(bucketName, null, false);

        observable.Subscribe(item =>
         {
             bucketKeys.Add(item.Key.ToString());
         },
        ex => Console.WriteLine("OnError: {0}", ex),
        () =>
        {
            _tcs.TrySetResult(bucketKeys);
        });

        return _tcs.Task.Result;
    }

    asp.net
    asp.netcore
    MinioClient
    ListObjectsAsync
    IObservable

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