Azure Service Fabric : How to find out if an Actor already exists - azure

Question

How can I find out if an Actor with a certain ActorId exists?
The ActorProxy is only for creating an Actor. If a non-existing Id is provided, and the Actor does not exist, a new Actor is created.
The standard ActorService can retrieve all Actors, but thats about it as far as I can see.

Answer 1

Currently there's no simple way of doing this. Actors are meant to abstract away the lifetime of an object's instance. Just call one when you need it, and it will be there. So I'm not sure this is really needed.
That said, you could create another service method to iterate through all the actors on the server-side instead of pulling the entire list to the client, but if you have millions of actor instances, it won't be very efficient.
Alternatively, you could store a marker state during your actor's initialization, and query the state provider for it - at the expense of adding more state and replication overhead to your actor.
First, create a service interface:
public interface IActorServiceEx : IService
{
Task<bool> ActorExists(ActorId actorId, CancellationToken cancellationToken = default(CancellationToken));
}
Then, create a custom actor service that implements this interface:
internal class CustomActorService : ActorService, IActorServiceEx
{
public CustomActorService(StatefulServiceContext context, ActorTypeInformation actorTypeInfo, Func<ActorBase> actorFactory = null, IActorStateProvider stateProvider = null, ActorServiceSettings settings = null)
: base(context, actorTypeInfo, actorFactory, stateProvider, settings)
{
}
public async Task<bool> ActorExists(ActorId actorId, CancellationToken cancellationToken)
{
const int batchSize = 1000;
ContinuationToken token = null;
do
{
var actors = await StateProvider.GetActorsAsync(batchSize, token, cancellationToken);
if (actors.Items.Contains(actorId))
{
return true;
}
token = actors.ContinuationToken;
} while (token != null);
return false;
}
}
Or the alternate version using the marker:
internal class Actor1 : Actor, IActor1
{
protected override async Task OnActivateAsync()
{
await StateManager.TryAddStateAsync("Activated", true);
}
}
internal class CustomActorService : ActorService, IActorServiceEx
{
...
public Task<bool> ActorExists(ActorId actorId, CancellationToken cancellationToken)
{
return StateProvider.ContainsStateAsync(actorId, "Activated", cancellationToken);
}
}
Finally, use it in when registering your actor, e.g.:
ActorRuntime.RegisterActorAsync<Actor1>((context, actorType) =>
new CustomActorService(context, actorType,
() => new Actor1())).GetAwaiter().GetResult();
And to call this new service method:
var actorService = ActorServiceProxy.Create<IActorServiceEx>(serviceUri, actorId);
var exists = await actorService.ActorExists(actorId);