C# async within an action

The problem is in this line:

return new Action(async () => ...

You start an async operation with the async lambda, but don’t return a task to await on. I.e. it runs on worker threads, but you’ll never find out when it’s done. And your program terminates before the async operation is complete -that’s why you don’t see any output.

It needs to be:

return new Func<Task>(async () => ...

UPDATE

First, you need to split responsibilities of methods, so you don’t mix retry policy (which should not be hardcoded to a check of a boolean result) with running tasks in parallel.

Then, as previously mentioned, you run your while (true) loop 100 times instead of doing things in parallel.

As @MachineLearning pointed out, use Task.Delay instead of Thread.Sleep.

Overall, your solution looks like this:

using System.Collections.Async;

static async Task DoWithRetries(Func<Task> action, int retryCount, string method)
{
    while (true)
    {
        try
        {
            await action();
            break;
        }
        catch (Exception e)
        {
            LoggerAgent.LogException(e, method);
        }

        if (retryCount <= 0)
            break;

        retryCount--;
        await Task.Delay(millisecondsDelay: 200);
    };
}

static async Task Example()
{
    List<int> ints = new List<int>();
    for (int i = 0; i < 1000; i++)
        ints.Add(i);

    Func<int, Task> actionOnItem =
        async item =>
        {
            await DoWithRetries(async () =>
            {
                List<string> test = await fetchSmthFromDb();
                Console.WriteLine("#" + item + "  " + test[0]);
                if (test[0] != "test")
                    throw new InvalidOperationException("unexpected result"); // will be re-tried
            },
            retryCount: 5,
            method: "test");
        };

    await ints.ParallelForEachAsync(actionOnItem, maxDegreeOfParalellism: 100);
}

You need to use the AsyncEnumerator NuGet Package in order to use the ParallelForEachAsync extension method from the System.Collections.Async namespace.