HSet

A HSet list is a distributed list corresponding to a cluster-side List which can be considered as a distributed implementation of the well-known C# IHashSet<T>. A HSet is a specialized IHCollection.

The set behavior can be configured on the server: see the general List documentation for complete details about sets.

Defining Sets

Sets are fully identified by their type and unique name, regardless of the types specified for set items. In other words, an HSet<string> and an HSet<int> named with the same name are backed by the same cluster structure. Obviously, refering to a set with types other than the expected types can have unspecified consequences (probably, serialization errors) and is not recommended.

The items type can be just about any valid .NET type, provided that it can be (de)serialized by the Hazelcast .NET Client (see the Serialization documentation). It does not necessarily need to be (de)serializable by the cluster, as long as the cluster does not need to handle them as objects, and can treat them as plain binary blobs. As soon as the cluster needs to handle the objects themselves, the types must also be (de)serializable by the cluster.

Creating & Destroying Sets

A set is obtained from the Hazelcast .NET Client, and is created on-demand: if a set with the specified name already exists on the cluster, it is returned, otherwise it is created on the cluster. For instance:

var set = await client.GetSetAsync<string>("my-set");

Sets should be disposed after usage, in order to release their resources. Note that this only releases client-side resources, but the actual data remain available on the cluster for further usage. In order to wipe the set and its data entirely from the cluster, it needs to be destroyed:

await set.DestroyAsync();

Using Sets

The HSet structure is completely documented in the associated IHSet<T> reference documentation. It provides methods to manipulate entries, such as:

  • AddAsync(item) adds an item to the set
  • GetAllAsync() retrieves the items
  • ContainsAsync(item) determines whether the set contains an item
  • GetSizeAsync() gets the number of items, and IsEmptyAsync() determines whether the map is empty
  • RemoveAsync(item) remove an item

The HSet structure exposes events (see events general documentation) at set level. A complete list of events is provided in the CollectionItemEventHandlers<T> documentation. The following example illustrates how to subscribe, and unsubscribe, to set events:

var id = await set.SubscribeAsync(events => events
    .ItemAdded((sender, args) => {
        logger.LogInformation($"Item {args.Item} was added.")
    }));

// ...

await set.UnsubscribeAsync(id);

Note that the handler methods passed to e.g. EntryRemoved or Cleared can be asynchronous, too.