Async Await Persistant Warning

Question

I am getting the warning "This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread. Although it sounds obvious, I thought I was covered because I run all the processes and have an Await Task.WhenAll() in my processFiles method. Do I need to be doing this a different way? Any thoughts would be kindly appreciated.

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Data.SqlClient;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Windows.Forms;
    using System.IO;


    namespace ProcessFiles
    {
        public partial class ProcessFiles : Form 
        {
            public ProcessFiles(int userLevel, int userID)
            {
            }

            private void btnProcess_Click(object sender, EventArgs e)
            {
                processFiles();

            }

            async Task<int> processFiles()
            {
                var processingTasks = new List<Task>();
                foreach (string fileName in listBox1.Items)
                {
                    processingTasks.Add(process012(fileName));
                    processingTasks.Add(process123(fileName));
                    processingTasks.Add(process234(fileName));

                }
                await Task.WhenAll(processingTasks);
                return (1);
            }


            async Task<int> process173(string fileName)
            {
                return (retVal);

            }

            async Task<int> process032(string fileName)
            {
                return (retVal);
            }

            async Task<int> process018(string fileName)
            {
                return (retVal);
            }

You have 3 methods with the async keyword but no await. Isn't the message clear? Also, if you want to return a completed task use return Task.FromResult without async — Panagiotis Kanavos
I thought await Task.WhenAll(processingTasks); was sufficient to wait for everything to complete. The last three methods don't have an await in them. — Missy
they have an async which means they need an await. And so does btnProcess_Click — Panagiotis Kanavos

Milen Milen · Accepted Answer · 2016-12-13T17:33:14

No need to use async Task in your processXXX methods just return Task<int> instead. You will await the tasks in main processFiles() method:

        private async void btnProcess_Click(object sender, EventArgs e)
        {
            await processFiles();
        }

        async Task<int> processFiles()
        {
            var processingTasks = new List<Task>();
            foreach (string fileName in listBox1.Items)
            {
                processingTasks.Add(process012(fileName));
                processingTasks.Add(process123(fileName));
                processingTasks.Add(process234(fileName));

            }
            await Task.WhenAll(processingTasks);
            return (1);
        }


        Task<int> process173(string fileName)
        {
            return Task.FromResult(retVal)
        }

        Task<int> process032(string fileName)
        {
            return Task.FromResult(retVal)
        }

        Task<int> process018(string fileName)
        {
           return Task.FromResult(retVal)
        }

Async Await Persistant Warning

1 Answers