how to cast async Func or Action to Delegate and invoke it

Question

I'm trying to make this code working:

protected async Task RunIsolated<TServ1, TServ2>(Action<TServ1, TServ2> action)
{
    await RunInScope(action, typeof(TServ1), typeof(TServ2));
}

protected async Task<TResult> RunIsolatedForResult<TService, TResult>(Func<TService, TResult> func)
{
    return (TResult) await RunInScope(func, typeof(TService));
}

private Task<object> RunInScope(Delegate d, params object[] args)
{
     using (var scope = _serviceProvider.CreateScope())
     {
         object[] parameters = args.Cast<Type>().Select(t => scope.ServiceProvider.GetService(t)).ToArray();
         return Task.FromResult(d.DynamicInvoke(parameters));
     }
}

this work for sync version of code, like this:

await RunIsolated<Service>(serv => serv.SaveAsync(item).Wait());

but don't work (db operation throw an exception) for async version of the same code

await RunIsolated<Service>(async serv => await serv.SaveAsync(item));

Is it somehow possible to convert async Action or Func to Delegate and invoke it without loosing async state?

Answer 1

You need to create new overload which accepts Func<Task>. Right now, anonymous async function you pass here

await RunIsolated<Service>(async serv => await serv.SaveAsync(item));

Is treated as Action, which means that is async void method basically, with all corresponding drawbacks. Instead you have to do something like this (simplified to use basic Action and Func, adjust as needed to your situation):

protected Task RunIsolated(Action action) {
    return RunInScope(action);
}

protected Task RunIsolated(Func<Task> action) {
    return RunInScope(action);
}

protected Task<TResult> RunIsolatedForResult<TResult>(Func<Task<TResult>> action) {
    return RunInScopeWithResult<TResult>(action);
}

protected Task<TResult> RunIsolatedForResult<TResult>(Func<TResult> action) {
    return RunInScopeWithResult<TResult>(action);
}

private async Task RunInScope(Delegate d, params object[] args) {
    // do some stuff
    using (var scope = _serviceProvider.CreateScope()) {
        object[] parameters = args.Cast<Type>().Select(t => scope.ServiceProvider.GetService(t)).ToArray();
        var result = d.DynamicInvoke(parameters);
        var resultTask = result as Task;
        if (resultTask != null) {
            await resultTask;
        }
    }
}

private async Task<TResult> RunInScopeWithResult<TResult>(Delegate d, params object[] args) {
    // do some stuff
    using (var scope = _serviceProvider.CreateScope()) {
        object[] parameters = args.Cast<Type>().Select(t => scope.ServiceProvider.GetService(t)).ToArray();
        var result = d.DynamicInvoke(parameters);
        var resultTask = result as Task<TResult>;
        if (resultTask != null) {
            return await resultTask;
        }
        return (TResult) result;
    }
}