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A discovery provider provides the ability to load a discovery cache. A discovery cache allows its creator to advertise entities it owns by periodically broadcasting Entity State Advertisements (ESAs) to remote caches. Applications can register discovery event handlers with the cache to receive updates aboute about newly added entities on remote caches or entities removed either explicitly by the remote cache or by virtue of stale entities "aging out" when ESAs are not received for an entity after some time.
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Advertisements use an internal binary protocol and communicate the following information for each entity. A discovery cache will periodically broadcast ESAs to prevent remote caches for from declaring them dead.
| Field | Description |
|---|---|
| Entity Owner | The unique id of the discovery cache that advertised the entity |
| Entity Type | The type of entity. Talon uses:
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| Entity Name | The unique name of the entity being advertised. |
| Entity Instance | The unique instance identifier for the entity. For example an ODS Store Member would have the same name in each XVM for the same application, but would have uniquely identifiable instance id. |
| Entity Host | The host from which the entity was advertised. |
| Entity Address Descriptors | Each entity added to the cache includes a list of adress descriptors that contain connection information that can be used by |
| Entity Age | Get an entity's current age. See |
| Entity Max Age | Each entity instance is associated with a maximum age and, at any point in time, a current age. A cache member 'expires' (removes from its local cache) a discovered entity when its current age reaches its maximum age. To prevent entity expiry, member owners periodically broadcast ESA (Entity State Advertisement) packets. The receipt of a ESA by non-owner causes the entity's age to be reset. An entity's maximum age is also used (in conjunction with other configurable parameters) by owner members to determine when to send ESAs. |
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