Events

Events in the Hazelcast .NET Client rely on a handler-based model close to the C# event model, though with a different syntax for adding and removing handlers, due to the asynchronous nature of these operations. Indeed, the following code has limitations:

thing.Updated += OnThingUpdated;
thing.Deleted += OnThingDeleted;

Here,

  • The two operations are distinct, whereas Hazelcast supports subscriptions that handle multiple events at once;
  • The subscription (+= operation) is synchronous, whereas Hazelcast needs to notify the members of the subscription;
  • The handlers (e.g. OnThingUpdated) are synchronous.

To overcome these limitations, the Hazelcast .NET Client uses the following syntax:

var id = await thing.SubscribeAsync(events => events
    .Updated(OnThingUpdated)
    .Deleted(OnThingDeleted));

Here, the handlers can be synchronous, for instance:

private void OnThingUpdated(Thing sender, ThingUpdatedEventArgs args)
{ 
    ...
}

But they can also be asynchronous, for instance:

private async ValueTask OnThingUpdated(Thing sender, ThingUpdatedEventArgs args)
{
    await ...
}

In the example, the two events are subscribed at once and that subscription is represented by the returned id, which is a Guid. The two events can only be unsubscribed at once too, by passing this id:

await thing.UnsubscribeAsync(id);

Client Events

The IHazelcastClient exposes the following events:

  • StateChanged triggers when the client state changes (TODO: link to client lifecycle doc)
  • PartitionLost triggers when (TODO: complete)
  • PartitionsUpdated triggers when the partitions table is updated
  • MembersUpdated triggers when the members list is updated
  • ObjectCreated triggers when a distributed object is created
  • ObjectDestroyed triggers when a distributed object is destroyed

TODO: detail each event args

Distributed Objects Events

TODO: complete