Package com.yahoo.vespa.curator.api

Interface VespaCurator.SingletonWorker

All Known Implementing Classes:
AbstractSingletonWorker
Enclosing interface:
VespaCurator
public static interface VespaCurator.SingletonWorker
Callback interface for processes of which only a single instance should be active at any time, across all containers in the cluster, and across all component generations. Notes:
  • activate() is called by the system on a singleton whenever it is the newest registered singleton in this container, and this container has the lease for the ID with which the singleton was registered. See VespaCurator.registerSingleton(java.lang.String, com.yahoo.vespa.curator.api.VespaCurator.SingletonWorker) and VespaCurator.isActive(java.lang.String).
  • deactivate() is called by the system on a singleton which is currently active whenever the above no longer holds. See VespaCurator.unregisterSingleton(com.yahoo.vespa.curator.api.VespaCurator.SingletonWorker).
  • Callbacks for the same ID are always invoked by the same thread, in serial; the callbacks must return in a timely manner, but are allowed to throw exceptions.
  • Activation and deactivation may be triggered by:
    1. the container acquiring or losing the activation lease; or
    2. registration of unregistration of a new or obsolete singleton.
    Events triggered by the latter happen synchronously, and errors are propagated to the caller for cleanup. Events triggered by the former may happen in the background, and because the system tries to always have one activated singleton, exceptions during activation will cause the container to abandon its lease, so another container may obtain it instead; exceptions during deactivation are only logged.
  • A container without any registered singletons will not attempt to hold the activation lease.
See AbstractSingletonWorker for an abstract superclass to use for implementations.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    activate()
    Called by the system whenever this singleton becomes the single active worker.
    void
    deactivate()
    Called by the system whenever this singleton is no longer the single active worker.

  • Method Details

    • activate

      void activate()
      Called by the system whenever this singleton becomes the single active worker. If this is triggered because the container obtains the activation lease, and activation fails, then the container immediately releases the lease, so another container may acquire it instead.

    • deactivate

      void deactivate()
      Called by the system whenever this singleton is no longer the single active worker.