/// <summary>
/// <para>
/// <see cref="PersistenceIds"/> is used for retrieving all `persistenceIds` of all
/// persistent actors.
/// </para>
/// The returned event stream is unordered and you can expect different order for multiple
/// executions of the query.
/// <para>
/// The stream is not completed when it reaches the end of the currently used `persistenceIds`,
/// but it continues to push new `persistenceIds` when new persistent actors are created.
/// Corresponding query that is completed when it reaches the end of the currently
/// currently used `persistenceIds` is provided by <see cref="CurrentPersistenceIds"/>.
/// </para>
/// The SQL write journal is notifying the query side as soon as new `persistenceIds` are
/// created and there is no periodic polling or batching involved in this query.
/// <para>
/// The stream is completed with failure if there is a failure in executing the query in the
/// backend journal.
/// </para>
/// </summary>
public Source <string, NotUsed> PersistenceIds()
{
lock (_lock)
{
if (_persistenceIdsPublisher is null)
{
var graph =
Source.ActorPublisher <string>(
LivePersistenceIdsPublisher.Props(
_refreshInterval,
_writeJournalPluginId))
.ToMaterialized(Sink.DistinctRetainingFanOutPublisher <string>(PersistenceIdsShutdownCallback), Keep.Right);
_persistenceIdsPublisher = graph.Run(_system.Materializer());
}
return(Source.FromPublisher(_persistenceIdsPublisher)
.MapMaterializedValue(_ => NotUsed.Instance)
.Named("AllPersistenceIds"));
}
}
