c# - How to use Task.WhenAny and implement retry

Question

I have a solution that creates multiple I/O based tasks and I'm using Task.WhenAny() to manage these tasks. But often many of the tasks will fail due to network issue or request throttling etc.

I can't seem to find a solution that enables me to successfully retry failed tasks when using a Task.WhenAny() approach.

Here is what I'm doing:

var tasks = new List<Task<MyType>>();
foreach(var item in someCollection)
{
   task.Add(GetSomethingAsync());
}
while (tasks.Count > 0)
{
   var child = await Task.WhenAny(tasks);
   tasks.Remove(child);
   ???
}

So the above structure works for completing tasks, but I haven't found a way to handle and retry failing tasks. The await Task.WhenAny throws an AggregateException rather than allowing me to inspect a task status. When In the exception handler I no longer have any way to retry the failed task.

Answer 1

I believe it would be easier to retry within the tasks, and then replace the Task.WhenAny-in-a-loop antipattern with Task.WhenAll

E.g., using Polly:

var tasks = new List<Task<MyType>>();
var policy = ...; // See Polly documentation
foreach(var item in someCollection)
  tasks.Add(policy.ExecuteAsync(() => GetSomethingAsync()));
await Task.WhenAll(tasks);

or, more succinctly:

var policy = ...; // See Polly documentation
var tasks = someCollection.Select(item => policy.ExecuteAsync(() => GetSomethingAsync()));
await Task.WhenAll(tasks);