Package org.apache.sling.discovery.commons.providers

Class BaseTopologyView

java.lang.Object
org.apache.sling.discovery.commons.providers.BaseTopologyView
All Implemented Interfaces:
TopologyView
Direct Known Subclasses:
DefaultTopologyView
public abstract class BaseTopologyView extends Object implements TopologyView
Very simple abstract base class for the TopologyView which comes with the 'setNotCurrent()' method - that allows the ViewStateManager to mark a topologyView as no longer current - and the isCurrent() is handled accordingly.

  • Constructor Details

    • BaseTopologyView

      public BaseTopologyView()

  • Method Details

    • isCurrent

      public boolean isCurrent()
      Checks if this TopologyView is currently valid - or if the service knows of a topology change just going on (or another uncertainty about the topology such as IOException etc)
      Specified by:
      isCurrent in interface TopologyView
      Returns:
      true if this TopologyView is currently valid, false if the service knows of a topology change just going on (or another issue with discovery like IOException etc)

    • setNotCurrent

      public void setNotCurrent()
      Marks this view as no longer current - this typically results in a TOPOLOGY_CHANGING event to be sent.

      Note that once marked as not current, it can no longer be reverted to current==true

    • getLocalClusterSyncTokenId

      public abstract String getLocalClusterSyncTokenId()
      Returns the id that shall be used in the syncToken by the ClusterSyncService.

      The clusterSyncId uniquely identifies each change of the local cluster for all participating instances. That means, all participating instances know of the clusterSyncId and it is the same for all instances. Whenever an instance joins/leaves the cluster, this clusterSyncId must change.

      Since this method returns the *local* clusterSyncId, it doesn't care if a remote cluster experienced changes - it must only change when the local cluster changes. However, it *can* change when a remote cluster changes too. So the requirement is just that it changes *at least* when the local cluster changes - but implementations can opt to regard this rather as a TopologyView-ID too (ie an ID that identifies a particular incarnation of the TopologyView for all participating instances in the whole topology).

      This id can further safely be used by the ClusterSyncService to identify a syncToken that it writes and that all other instances in the lcoal cluster wait for, before sending a TOPOLOGY_CHANGED event.

      Note that this is obviously not to be confused with the ClusterView.getId() which is stable throughout the lifetime of a cluster.

    • toShortString

      public String toShortString()

    • getInstance

      public InstanceDescription getInstance(String slingId)
      Simple getter for a particular slingId
      Parameters:
      slingId - the slingId for which to lookup the InstanceDescription
      Returns:
      the InstanceDescription matching the provided slingId - or null if it doesn't exist