GOSSIP-62 Implement Crdt PN-Counter

restored layout of pom.xml for minimal changes in PR

Snapshot - I think I have the basic framework in place. No tests are passing and nothing works, but most of the calls and the builder are in place.

capture working code

starting working on example code

Working examples

GOSSIP-65 Implement crdt LWW-Element-Set

LWWSet implemented + se/de + unit tests + jackson tests + DataTests

GOSSIP-55 Added event handlers to notify share data and per node data changes

Reformat code to match apache standard

Fixed DataTest errors WRT PNCounter
7 files changed
tree: ef6047ff2231241f65724d59c2b07a0b9e678588
  1. .gitignore
  2. .travis.yml
  6. README.md
  7. eclipse_template.xml
  8. gossip-base/
  9. gossip-examples/
  10. gossip-itest/
  11. gossip-protocol-jackson/
  12. gossip-transport-udp/
  13. pom.xml

Gossip Build status

Gossip protocol is a method for a group of nodes to discover and check the liveliness of a cluster. More information can be found at http://en.wikipedia.org/wiki/Gossip_protocol.

The original implementation was forked from https://code.google.com/p/java-gossip/. Several bug fixes and changes have already been added.

A set of easily-run examples, illustrating various features of Gossip, are available in the gossip-examples module. The README.md file, in that module described how to run those examples.

Below, a list of code snippits which show how to incorproate Apache Gossip into your project.


To gossip you need one or more seed nodes. Seed is just a list of places to initially connect to.

  GossipSettings settings = new GossipSettings();
  int seedNodes = 3;
  List<GossipMember> startupMembers = new ArrayList<>();
  for (int i = 1; i < seedNodes+1; ++i) {
    URI uri = new URI("udp://" + "" + ":" + (50000 + i));
    startupMembers.add(new RemoteGossipMember(cluster, uri, i + ""));

Here we start five gossip processes and check that they discover each other. (Normally these are on different hosts but here we give each process a distinct local ip.

  List<GossipService> clients = new ArrayList<>();
  int clusterMembers = 5;
  for (int i = 1; i < clusterMembers+1; ++i) {
    URI uri = new URI("udp://" + "" + ":" + (50000 + i));
   GossipService gossipService = new GossipService(cluster, uri, i + "",
             startupMembers, settings, (a,b) -> {});

Later we can check that the nodes discover each other

  for (int i = 0; i < clusterMembers; ++i) {
    Assert.assertEquals(4, clients.get(i).getGossipManager().getLiveMembers().size());

Usage with Settings File

For a very simple client setup with a settings file you first need a JSON file such as:

    {"cluster": "9f1e6ddf-8e1c-4026-8fc6-8585d0132f77","uri":"udp://"}


  • cluster - is the name of the cluster
  • id - is a unique id for this node (you can use any string, but above we use a UUID)
  • uri - is a URI object containing IP/hostname and port to use on the default adapter on the node's machine
  • gossip_interval - how often (in milliseconds) to gossip list of members to other node(s)
  • cleanup_interval - when to remove ‘dead’ nodes (in milliseconds) (deprecated may be coming back)
  • members - initial seed nodes

Then starting a local node is as simple as:

GossipService gossipService = new GossipService(
  StartupSettings.fromJSONFile( "node_settings.json" )

And then when all is done, shutdown with:


Event Listener

The status can be polled using the getters that return immutable lists.

   public List<LocalGossipMember> getLiveMembers()
   public List<LocalGossipMember> getDeadMembers()

These can be accessed from the GossipManager on your GossipService, e.g: gossipService.getGossipManager().getLiveMembers();

Users can also attach an event listener:

    GossipService gossipService = new GossipService(cluster, uri, i + "", startupMembers,
    settings, new GossipListener() {
      public void gossipEvent(GossipMember member, GossipState state) {
        System.out.println(System.currentTimeMillis() + " Member " + j + " reports "
                + member + " " + state);
  //The lambda syntax is (a,b) -> { }  //NICE!