C# Singleton - 使用异步等待触发并忘记

Question

Context - I am using Azure CosmosDB GraphAPI - and azure doesn't have logging for it, Sad! So we came up with using our own logging of queries and its metaproperties

I implemented a Singleton class that is used by other services for DB Calls and I want to have a fire and forget the call to the logger.

    public class GraphDatabaseQuery : IGraphDatabaseQuery
    {
        private readonly GremlinClient gremlinClient;
        public GraphDatabaseQuery()
        {
            if (gremlinClient == null)
            {
                gremlinClient = CosmosDbClient.Instance;
            }
            else
            {
                if (gremlinClient.NrConnections == 0)
                {
                    gremlinClient = CosmosDbClient.Instance;
                }
            }
        }

        public async Task<ResultSet<dynamic>> SubmitQueryAsync(string query, string fullName)
        {
            var response = await gremlinClient.SubmitAsync<dynamic>(query);
            _ = SendQueryAnalytics(response, query, fullName);
            return response;
        }
        public async Task<dynamic> SubmitQueryWithSingleSingleResultAsync(string query, string fullName)
        {
            var response = await gremlinClient.SubmitWithSingleResultAsync<dynamic>(query);
            return response;

        }

        private async Task<bool> SendQueryAnalytics(ResultSet<dynamic> response, string query, string fullName)
        {
            try
            {
                await new QueryAnalytics().pushData(response, query, fullName); // breakpoint here 
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            return true;
        }
    }

in startup.cs

            services.AddSingleton<IGraphDatabaseQuery, GraphDatabaseQuery>();

and the interface

    public interface IGraphDatabaseQuery
    {
        public Task<ResultSet<dynamic>> SubmitQueryAsync(string query, string fullName);
        public Task<dynamic> SubmitQueryWithSingleSingleResultAsync(string query, string fullName);

    }

Whenever I test it the breakpoint hits "SendQueryAnalytics" but i assume at that moment the response from the calling function would be sent back

is this not working because I am using the singleton pattern?

Answer 1

Whenever I test it the breakpoint hits "SendQueryAnalytics" but i assume at that moment the response from the calling function would be sent back

No. All asynchronous methods begin executing synchronously .

So what happens is that SendQueryAnalytics is called and begins executing, enters the try block, creates a new QueryAnalytics instance, and calls pushData . pushData also begins executing and (presumably) returns an incomplete Task . Then the await in SendQueryAnalytics observes that that Task is incomplete and returns an incomplete Task to SubmitQueryAsync , which discards that Task instance and then returns the response.

Thus, seeing the response returned after that breakpoint is normal.

Answer 2

I don't think that the singleton pattern has something to do with it. Since you want a 'fire and forget' why don't you use something like hangfire ?