Package akka.cluster.ddata

Class LWWMap<A,​B>

  • All Implemented Interfaces:
    DeltaReplicatedData, RemovedNodePruning, ReplicatedData, ReplicatedDataSerialization, java.io.Serializable
    public final class LWWMap<A,​B>
extends java.lang.Object
implements DeltaReplicatedData, ReplicatedDataSerialization, RemovedNodePruning
    Specialized ORMap with LWWRegister values.

    LWWRegister relies on synchronized clocks and should only be used when the choice of value is not important for concurrent updates occurring within the clock skew.

    Instead of using timestamps based on System.currentTimeMillis() time it is possible to use a timestamp value based on something else, for example an increasing version number from a database record that is used for optimistic concurrency control.

    The defaultClock is using max value of System.currentTimeMillis() and currentTimestamp + 1. This means that the timestamp is increased for changes on the same node that occurs within the same millisecond. It also means that it is safe to use the LWWMap without synchronized clocks when there is only one active writer, e.g. a Cluster Singleton. Such a single writer should then first read current value with ReadMajority (or more) before changing and writing the value with WriteMajority (or more).

    For first-write-wins semantics you can use the LWWRegister.reverseClock() instead of the LWWRegister.defaultClock()

    This class is immutable, i.e. "modifying" methods return a new instance.

    See Also:
    Serialized Form

    • Method Detail

      • empty

        public static <A,​B> LWWMap<A,​B> empty()

      • apply

        public static LWWMap<java.lang.Object,​java.lang.Object> apply()

      • create

        public static <A,​B> LWWMap<A,​B> create()
        Java API

      • unapply

        public static <A,​B> scala.Option<scala.collection.immutable.Map<A,​B>> unapply​(LWWMap<A,​B> m)
        Extract the entries().

      • entries

        public scala.collection.immutable.Map<A,​B> entries()
        Scala API: All entries of the map.

      • getEntries

        public java.util.Map<A,​B> getEntries()
        Java API: All entries of the map.

      • get

        public scala.Option<B> get​(A key)

      • contains

        public boolean contains​(A key)

      • isEmpty

        public boolean isEmpty()

      • size

        public int size()

      • put

        public LWWMap<A,​B> put​(SelfUniqueAddress node,
                             A key,
                             B value,
                             LWWRegister.Clock<B> clock)
        Adds an entry to the map.

        You can provide your clock implementation instead of using timestamps based on System.currentTimeMillis() time. The timestamp can for example be an increasing version number from a database record that is used for optimistic concurrency control.

      • remove

        public LWWMap<A,​B> remove​(SelfUniqueAddress node,
                                A key)
        Removes an entry from the map. Note that if there is a conflicting update on another node the entry will not be removed after merge.

      • resetDelta

        public LWWMap<A,​B> resetDelta()
        Description copied from interface: DeltaReplicatedData
        Reset collection of deltas from mutator operations. When the Replicator invokes the modify function of the Update message the delta is always "reset" and when the user code is invoking one or more mutator operations the data is collecting the delta of the operations and makes it available for the Replicator with the DeltaReplicatedData.delta() accessor. When the Replicator has grabbed the delta it will invoke this method to get a clean data instance without the delta.
        Specified by:
        resetDelta in interface DeltaReplicatedData

      • delta

        public scala.Option<ORMap.DeltaOp> delta()
        Description copied from interface: DeltaReplicatedData
        The accumulated delta of mutator operations since previous DeltaReplicatedData.resetDelta(). When the Replicator invokes the modify function of the Update message and the user code is invoking one or more mutator operations the data is collecting the delta of the operations and makes it available for the Replicator with the DeltaReplicatedData.delta() accessor. The modify function shall still return the full state in the same way as ReplicatedData without support for deltas.
        Specified by:
        delta in interface DeltaReplicatedData

      • modifiedByNodes

        public scala.collection.immutable.Set<UniqueAddress> modifiedByNodes()
        Description copied from interface: RemovedNodePruning
        The nodes that have changed the state for this data and would need pruning when such node is no longer part of the cluster.
        Specified by:
        modifiedByNodes in interface RemovedNodePruning

      • toString

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

      • equals

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

      • hashCode

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