Package su.onno.ui.presence

Class PresenceRegistry

java.lang.Object

su.onno.ui.presence.PresenceRegistry

public class PresenceRegistry
extends Object

In-memory registry of who is currently viewing each record, for record-level collaboration markers ("3 people are here", like the avatars in a shared document).

State is per-node and ephemeral: a (entityType, entityName, id) record maps to its set of viewers, each carrying a lastSeen stamped from this node's clock. A viewer is kept alive by heartbeats and expires by TTL when they stop arriving — so a closed tab or a crashed peer self-heals without an explicit leave, and no cross-node clock agreement is needed.

Two inputs feed the same map:

• Local — a browser on this node calls the presence endpoint (onLocal(java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.lang.String)); the change is applied, broadcast to peer nodes over the ClusterEventBus, and pushed to this node's SSE clients.
• Remote — a peer relayed a ClusterEvent.Presence over the bus (onRemote(su.onno.cluster.ClusterEvent.Presence)); it is applied and pushed to this node's SSE clients, but never re-broadcast (no relay loop).

An SSE snapshot is pushed only when a record's viewer set changes (a join or a leave), not on every heartbeat, so liveness traffic stays off the browser stream. Like everything on the cluster bus this is best-effort: a dropped ping costs at most one TTL of staleness.

All per-record mutations run inside the outer ConcurrentHashMap.compute(K, java.util.function.BiFunction<? super K, ? super V, ? extends V>) callback, so the inner plain maps are only ever touched while the bin lock is held — no separate synchronization is required, and an emptied record is dropped atomically without the classic remove-empty-inner-map race.

Field Summary

Fields

Modifier and Type	Field	Description
static final long	DEFAULT_SWEEP_INTERVAL_MILLIS	Default interval between expiry sweeps.
static final long	DEFAULT_TTL_MILLIS	Default viewer time-to-live: a viewer with no heartbeat for this long is dropped.

Constructor Summary

Constructors

Constructor	Description
PresenceRegistry(ClusterEventBus bus, UiEventPublisher publisher)

Method Summary

Modifier and Type	Method	Description
List<Map<String,Object>>	allViewers()	A snapshot of every record with viewers, as {kind, name, id, viewers} maps — the initial picture the ambient-presence store loads before live SSE deltas keep it current.
void	onLocal(String action, String kind, String entityName, String id, String userId, String displayName, String avatarUrl)	A browser on this node entered/refreshed/left a record.
void	onRemote(ClusterEvent.Presence presence)	A peer node relayed a presence change.
void	start()
void	stop()
void	sweepExpired()	Remove viewers whose last heartbeat predates the TTL, pushing a fresh snapshot for each affected record.
List<Map<String,String>>	viewers(String kind, String entityName, String id)	The current viewers of a record as {userId, displayName} maps — what the enter response returns.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DEFAULT_TTL_MILLIS

public static final long DEFAULT_TTL_MILLIS

Default viewer time-to-live: a viewer with no heartbeat for this long is dropped. ~3 missed beats.

See Also:

• Constant Field Values

DEFAULT_SWEEP_INTERVAL_MILLIS

public static final long DEFAULT_SWEEP_INTERVAL_MILLIS

Default interval between expiry sweeps.

See Also:

• Constant Field Values

Constructor Details

PresenceRegistry

public PresenceRegistry(ClusterEventBus bus,
 UiEventPublisher publisher)

Method Details

start

@PostConstruct
public void start()

stop

@PreDestroy
public void stop()

onLocal

public void onLocal(String action,
 String kind,
 String entityName,
 String id,
 String userId,
 String displayName,
 String avatarUrl)

A browser on this node entered/refreshed/left a record. Apply, relay to peers, fan out locally.

onRemote

public void onRemote(ClusterEvent.Presence presence)

A peer node relayed a presence change. Apply and fan out locally; never re-broadcast.

sweepExpired

public void sweepExpired()

Remove viewers whose last heartbeat predates the TTL, pushing a fresh snapshot for each affected record.

viewers

public List<Map<String,String>> viewers(String kind,
 String entityName,
 String id)

The current viewers of a record as {userId, displayName} maps — what the enter response returns.

allViewers

public List<Map<String,Object>> allViewers()

A snapshot of every record with viewers, as {kind, name, id, viewers} maps — the initial picture the ambient-presence store loads before live SSE deltas keep it current. Built under each record's bin lock, so it is internally consistent per record.