Leader.java

/*
 * Copyright 2016-present Open Networking Laboratory
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.onosproject.cluster;

import com.google.common.base.MoreObjects;
import com.google.common.base.Objects;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkArgument;

/**
 * Topic leader.
 * <p>
 * Identified by the {@link NodeId node identifier} and a monotonically increasing term number.
 * The term number is incremented by one every time a new node is elected as leader.
 * Also available is the system clock time at the instant when this node was elected as leader.
 * Keep in mind though that as with any system clock based time stamps this particular information
 * susceptible to clock skew and should only be relied on for simple diagnostic purposes.
 */
public class Leader {
    private final NodeId nodeId;
    private final long term;
    private final long termStartTime;

    public Leader(NodeId nodeId, long term, long termStartTime) {
        this.nodeId = checkNotNull(nodeId);
        checkArgument(term >= 0, "term must be non-negative");
        this.term = term;
        checkArgument(termStartTime >= 0, "termStartTime must be non-negative");
        this.termStartTime = termStartTime;
    }

    /**
     * Returns the identifier for of leader.
     * @return node identifier
     */
    public NodeId nodeId() {
        return nodeId;
    }

    /**
     * Returns the leader's term.
     * @return leader term
     */
    public long term() {
        return term;
    }

    /**
     * Returns the system time when the current leadership term started.
     * @return current leader term start time
     */
    public long termStartTime() {
        return termStartTime;
    }

    @Override
    public boolean equals(Object other) {
        if (this == other) {
            return true;
        }
        if (other != null && other instanceof Leader) {
            Leader that = (Leader) other;
            return Objects.equal(this.nodeId, that.nodeId) &&
                    this.term ==  that.term &&
                    this.termStartTime == that.termStartTime;
        }
        return false;
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(nodeId, term, termStartTime);
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(getClass())
            .add("nodeId", nodeId)
            .add("term", term)
            .add("termStartTime", termStartTime)
            .toString();
    }
}