com.netflix.eureka.lease.Lease Maven / Gradle / Ivy

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/*
 * Copyright 2012 Netflix, Inc.
 *
 *    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 com.netflix.eureka.lease;

import com.netflix.appinfo.InstanceInfo;
import com.netflix.eureka.InstanceRegistry;

/**
 * Describes a time-based availability of a {@link T}. Purpose is to avoid
 * accumulation of instances in {@link InstanceRegistry} as result of ungraceful
 * shutdowns that is not uncommon in AWS environments.
 * 
 * If a lease elapses without renewals, it will eventually expire consequently
 * marking the associated {@link T} for immediate eviction - this is similar to
 * an explicit cancellation except that there is no communication between the
 * {@link T} and {@link LeaseManager}.
 * 
 * @author Karthik Ranganathan, Greg Kim
 */
public class Lease {

    enum Action {
        Register, Cancel, Renew
    };

    public final static int DEFAULT_DURATION_IN_SECS = 90;

    private T holder;
    private long evictionTimestamp;
    private long registrationTimestamp;
    // Make it volatile so that the expiration task would see this quicker
    private volatile long lastUpdateTimestamp;
    private long duration;

    public Lease(T r, int durationInSecs) {
        holder = r;
        registrationTimestamp = System.currentTimeMillis();
        lastUpdateTimestamp = registrationTimestamp;
        duration = (durationInSecs * 1000);

    }

    /**
     * Renew the lease, use renewal duration if it was specified by the
     * associated {@link T} during registration, otherwise default duration is
     * {@link #DEFAULT_DURATION_IN_SECS}
     */
    public void renew() {
        lastUpdateTimestamp = System.currentTimeMillis() + duration;

    }

    /**
     * Cancels the lease by updating the eviction time.
     */
    public void cancel() {
        if (evictionTimestamp <= 0) {
            evictionTimestamp = System.currentTimeMillis();
        }
    }

    /**
     * Checks if the lease of a given {@link InstanceInfo} has expired or not.
     */
    public boolean isExpired() {
        return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration));
    }

    /**
     * Gets the milliseconds since epoch when the lease was registered.
     * 
     * @return the milliseconds since epoch when the lease was registered.
     */
    public long getRegistrationTimestamp() {
        return registrationTimestamp;
    }

    /**
     * Gets the milliseconds since epoch when the lease was last renewed.
     * 
     * @return the milliseconds since epoch when the lease was last renewed.
     */
    public long getLastRenewalTimestamp() {
        return lastUpdateTimestamp;
    }

    /**
     * Gets the milliseconds since epoch when the lease was evicted.
     * 
     * @return the milliseconds since epoch when the lease was evicted.
     */
    public long getEvictionTimestamp() {
        return evictionTimestamp;
    }

    /**
     * Returns the holder of the lease.
     */
    public T getHolder() {
        return holder;
    }

}