Using Polly for a retry attempt from an async function

Question

I'm trying to retry a failed operation 3 times.

I'm using Polly for a retry operation.

I want to get the exception in case the retry operation fails and retry again 2 times and so on.

return await Policy
           .Handle<CustomException>()
           .RetryAsync(3, onRetryAsync: async (exception, retryCount, context) =>
           {
               return await runner.run(params);
           });

The function should return

Task<IReadOnlyCollection<string>>

I'm getting the following error:

async lambda expression converted to a task returning delegate cannot return a value

Answer 1

I think it is unusual to run your logic in the retry policy - unless I misunderstand your question. More typically you execute the policy by calling a method that runs your logic.

Something like this:

async Task Main()
{
    var polly = Policy
           .Handle<Exception>()        
           .RetryAsync(3, (exception, retryCount, context) => Console.WriteLine($"try: {retryCount}, Exception: {exception.Message}"));

    var result = await polly.ExecuteAsync(async () => await DoSomething());
    Console.WriteLine(result);
}

int count = 0;

public async Task<string> DoSomething()
{
    if (count < 3)
    {
        count++;
        throw new Exception("boom");
    }

    return await Task.FromResult("foo");
}

output

try: 1, Exception: boom
try: 2, Exception: boom
try: 3, Exception: boom
foo