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

Class DefaultClusterView

  • All Implemented Interfaces:
    ClusterView
    Direct Known Subclasses:
    LocalClusterView
    public class DefaultClusterView
extends java.lang.Object
implements ClusterView
    Default implementation of the ClusterView interface.

    Besides implementing the interface methods it also adds add/remove of InstanceDescriptions as well as implementing equals and hashCode.

    • Constructor Detail

      • DefaultClusterView

        public DefaultClusterView​(java.lang.String id)

    • Method Detail

      • equals

        public boolean equals​(java.lang.Object obj)
        Overrides:
        equals in class java.lang.Object

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class java.lang.Object

      • getId

        public java.lang.String getId()
        Description copied from interface: ClusterView
        Returns a stable id of the cluster represented by this cluster view.

        Similar to the SlingID, this id is persisted and thus remains stable accross instance/cluster restarts.

        When an instance joins a cluster, it will inherit the id from the joined cluster (thus incurs a cluster id change).

        Note: When instances part from a cluster (eg due to a network partitioning) the cluster id is retained. This results in potentially multiple clusters with the same id. This fact could be used to detect such partitioning/split brain situations. It also implies though that the cluster id is not guaranteed to be unique in a topology!

        Addition in 1.0.4: this id must consist only of alphanumeric characters plus dash '-' and underscore '_'.

        Specified by:
        getId in interface ClusterView
        Returns:
        an id of this cluster view
        See Also:
        SLING-3164

      • addInstanceDescription

        public void addInstanceDescription​(DefaultInstanceDescription instance)
        Add the given instance to this cluster and set the cluster on the instance (back pointer)
        Parameters:
        instance - the instance to add to this cluster

      • getInstances

        public java.util.List<InstanceDescription> getInstances()
        Description copied from interface: ClusterView
        Provides the list of InstanceDescriptions with a stable ordering.

        Stable ordering implies that unless an instance leaves the cluster (due to shutdown/crash/network problems) the instance keeps the relative position in the list.

        Specified by:
        getInstances in interface ClusterView
        Returns:
        the list of InstanceDescriptions (with a stable ordering)

      • getLeader

        public InstanceDescription getLeader()
        Description copied from interface: ClusterView
        Provides the InstanceDescription belonging to the leader instance.

        Every ClusterView is guaranteed to have one and only one leader.

        The leader is stable: once a leader is elected it stays leader unless it leaves the cluster (due to shutdown/crash/network problems)

        Specified by:
        getLeader in interface ClusterView
        Returns:
        the InstanceDescription belonging to the leader instance

      • removeInstanceDescription

        public boolean removeInstanceDescription​(InstanceDescription instance)
        Removes the given instance from this cluster.

        Note that the instance will still have a pointer to this cluster however.

        Parameters:
        instance - the instance to remove from this cluster

      • getLocalInstance

        public InstanceDescription getLocalInstance()
        Returns the local InstanceDescription or null if no local instance is listed
        Returns:
        the local InstanceDescription or null if no local instance is listed
        Throws:
        java.lang.IllegalStateException - if multiple local instances are listed