replication is configured, any incoming uploads and metadata changes to versions created on the target, will sync back to the source and be marked as `REPLICA` on the source. AWS, as well as MinIO do not by default sync metadata changes on a object version marked `REPLICA` back to source. This requires a setting in the replication configuration called [replica modification sync](https://aws.amazon.com/about-aws/whats-new/2020/12/amazon-s3-replication-adds-support-two-way-replication/).

For active-active...

  ASSERT_TRUE(TF_GetCode(status.get()) == TF_OK) << TF_Message(status.get());

  std::vector<std::string> devices{
      "/job:localhost/replica:0/task:0/device:CPU:0",
      "/job:localhost/replica:0/task:0/device:CPU:1"};
  ParallelDevice parallel_device(std::move(devices));
  std::unique_ptr<TFE_Op, decltype(&TFE_DeleteOp)> handle_op(

    if (replica.containsKey(newValue)) {
      replica.get(newValue).incrementAndGet();
    } else {
      replica.put(newValue, new AtomicInteger(1));
    }
  }

  private static void removeMinFromReplica(
      SortedMap<Integer, AtomicInteger> replica, int minValue) {
    Integer replicatedMinValue = replica.firstKey();

    if (replica.containsKey(newValue)) {
      replica.get(newValue).incrementAndGet();
    } else {
      replica.put(newValue, new AtomicInteger(1));
    }
  }

  private static void removeMinFromReplica(
      SortedMap<Integer, AtomicInteger> replica, int minValue) {
    Integer replicatedMinValue = replica.firstKey();

        when {
          startsWith('"'.code.toByte()) -> readQuotedString()
          else -> readToken()
        } ?: return // Expected a value.

      val replaced = parameters.put(peek, parameterValue)
      peek = null
      if (replaced != null) return // Unexpected duplicate parameter.
      if (!skipCommasAndWhitespace() && !exhausted()) return // Expected ',' or EOF.
    }

        // replaces?
        AbstractRepositoryMetadata repoMetadata = (AbstractRepositoryMetadata) metadata;
        this.metadata.merge(repoMetadata.getMetadata());
    }

    public void merge(ArtifactMetadata metadata) {
        // TODO not sure that it should assume this, maybe the calls to addMetadata should pre-merge, then artifact
        // replaces?

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(
            RemovalNotification.create("one", 1, RemovalCause.EXPLICIT),
            RemovalNotification.create("one", 1, RemovalCause.REPLACED))
        .addEqualityGroup(RemovalNotification.create("1", 1, RemovalCause.EXPLICIT))
        .addEqualityGroup(RemovalNotification.create("one", 2, RemovalCause.EXPLICIT))
        .testEquals();
  }

  TFE_OpReset(reused_op.get(), "Identity",
              "/job:localhost/replica:0/task:0/device:CPU:0", status.get());
  ASSERT_TRUE(TF_GetCode(status.get()) == TF_OK) << TF_Message(status.get());
  ASSERT_EQ(tensorflow::string(TFE_OpGetDevice(reused_op.get(), status.get())),
            tensorflow::string("/job:localhost/replica:0/task:0/device:CPU:0"));
  ASSERT_TRUE(TF_GetCode(status.get()) == TF_OK) << TF_Message(status.get());
}

  EXPECT_EQ(TF_OK, TF_GetCode(status.get())) << TF_Message(status.get());

  const char* first_device = "/job:worker/replica:0/task:1/device:CPU:0";
  const char* second_device = "/job:worker/replica:0/task:2/device:CPU:0";
  const char* device_name = "/job:localhost/replica:0/task:0/device:CUSTOM:0";
  std::array<const char*, 2> underlying_devices{first_device, second_device};

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(
            RemovalNotification.create("one", 1, RemovalCause.EXPLICIT),
            RemovalNotification.create("one", 1, RemovalCause.REPLACED))
        .addEqualityGroup(RemovalNotification.create("1", 1, RemovalCause.EXPLICIT))
        .addEqualityGroup(RemovalNotification.create("one", 2, RemovalCause.EXPLICIT))
        .testEquals();
  }