/*
* Copyright 2014-2017 the original author or authors.
*
* 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.springframework.integration.zookeeper.leader;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.imps.CuratorFrameworkState;
import org.apache.curator.framework.recipes.leader.LeaderSelector;
import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter;
import org.springframework.context.SmartLifecycle;
import org.springframework.integration.leader.Candidate;
import org.springframework.integration.leader.Context;
import org.springframework.integration.leader.event.LeaderEventPublisher;
import org.springframework.util.StringUtils;
/**
* Bootstrap leadership {@link Candidate candidates}
* with ZooKeeper/Curator. Upon construction, {@link #start} must be invoked to
* register the candidate for leadership election.
*
* @author Patrick Peralta
* @author Janne Valkealahti
* @author Gary Russell
* @author Artem Bilan
*
* @since 4.2
*/
public class LeaderInitiator implements SmartLifecycle {
private static final Log logger = LogFactory.getLog(LeaderInitiator.class);
private static final String DEFAULT_NAMESPACE = "/spring-integration/leader/";
private static final Context NULL_CONTEXT = () -> false;
private final CuratorContext context = new CuratorContext();
/**
* Curator client.
*/
private final CuratorFramework client;
/**
* Candidate for leader election.
*/
private final Candidate candidate;
private final Object lifecycleMonitor = new Object();
/**
* Curator utility for selecting leaders.
*/
private volatile LeaderSelector leaderSelector;
/**
* @see SmartLifecycle
*/
private volatile boolean autoStartup = true;
/**
* @see SmartLifecycle which is an extension of org.springframework.context.Phased
*/
private volatile int phase;
/**
* Flag that indicates whether the leadership election for
* this {@link #candidate} is running.
*/
private volatile boolean running;
/** Base path in a zookeeper */
private final String namespace;
/** Leader event publisher if set */
private volatile LeaderEventPublisher leaderEventPublisher;
/**
* Construct a {@link LeaderInitiator}.
*
* @param client Curator client
* @param candidate leadership election candidate
*/
public LeaderInitiator(CuratorFramework client, Candidate candidate) {
this(client, candidate, DEFAULT_NAMESPACE);
}
/**
* Construct a {@link LeaderInitiator}.
*
* @param client Curator client
* @param candidate leadership election candidate
* @param namespace namespace base path in zookeeper
*/
public LeaderInitiator(CuratorFramework client, Candidate candidate, String namespace) {
this.client = client;
this.candidate = candidate;
this.namespace = namespace;
}
/**
* @return true if leadership election for this {@link #candidate} is running
*/
@Override
public boolean isRunning() {
return this.running;
}
@Override
public int getPhase() {
return this.phase;
}
/**
* @param phase the phase
* @see SmartLifecycle
*/
public void setPhase(int phase) {
this.phase = phase;
}
@Override
public boolean isAutoStartup() {
return this.autoStartup;
}
/**
* @param autoStartup true to start automatically
* @see SmartLifecycle
*/
public void setAutoStartup(boolean autoStartup) {
this.autoStartup = autoStartup;
}
/**
* Start the registration of the {@link #candidate} for leader election.
*/
@Override
public void start() {
synchronized (this.lifecycleMonitor) {
if (!this.running) {
if (this.client.getState() != CuratorFrameworkState.STARTED) {
// we want to do curator start here because it needs to
// be started before leader selector and it gets a little
// complicated to control ordering via beans so that
// curator is fully started.
this.client.start();
}
this.leaderSelector = new LeaderSelector(this.client, buildLeaderPath(), new LeaderListener());
this.leaderSelector.setId(this.candidate.getId());
this.leaderSelector.autoRequeue();
this.leaderSelector.start();
this.running = true;
logger.debug("Started LeaderInitiator");
}
}
}
/**
* Stop the registration of the {@link #candidate} for leader election.
* If the candidate is currently leader, its leadership will be revoked.
*/
@Override
public void stop() {
synchronized (this.lifecycleMonitor) {
if (this.running) {
this.leaderSelector.close();
this.running = false;
logger.debug("Stopped LeaderInitiator");
}
}
}
@Override
public void stop(Runnable runnable) {
stop();
runnable.run();
}
/**
* Sets the {@link LeaderEventPublisher}.
*
* @param leaderEventPublisher the event publisher
*/
public void setLeaderEventPublisher(LeaderEventPublisher leaderEventPublisher) {
this.leaderEventPublisher = leaderEventPublisher;
}
/**
* The context of the initiator or null if not running.
* @return the context (or null if not running)
* @since 5.0
*/
public Context getContext() {
if (this.leaderSelector == null) {
return NULL_CONTEXT;
}
return this.context;
}
/**
* @return the ZooKeeper path used for leadership election by Curator
*/
private String buildLeaderPath() {
String ns = StringUtils.hasText(this.namespace) ? this.namespace : DEFAULT_NAMESPACE;
if (!ns.startsWith("/")) {
ns = "/" + ns;
}
if (!ns.endsWith("/")) {
ns = ns + "/";
}
return ns + this.candidate.getRole();
}
/**
* Implementation of Curator leadership election listener.
*/
protected class LeaderListener extends LeaderSelectorListenerAdapter {
@Override
public void takeLeadership(CuratorFramework framework) throws Exception {
try {
LeaderInitiator.this.candidate.onGranted(LeaderInitiator.this.context);
if (LeaderInitiator.this.leaderEventPublisher != null) {
try {
LeaderInitiator.this.leaderEventPublisher.publishOnGranted(LeaderInitiator.this,
LeaderInitiator.this.context, LeaderInitiator.this.candidate.getRole());
}
catch (Exception e) {
logger.warn("Error publishing OnGranted event.", e);
}
}
// when this method exits, the leadership will be revoked;
// therefore this thread needs to be held up until the
// candidate is no longer leader
Thread.sleep(Long.MAX_VALUE);
}
catch (InterruptedException e) {
// InterruptedException, like any other runtime exception,
// is handled by the finally block below. No need to
// reset the interrupt flag as the interrupt is handled.
}
finally {
LeaderInitiator.this.candidate.onRevoked(LeaderInitiator.this.context);
if (LeaderInitiator.this.leaderEventPublisher != null) {
try {
LeaderInitiator.this.leaderEventPublisher.publishOnRevoked(LeaderInitiator.this,
LeaderInitiator.this.context, LeaderInitiator.this.candidate.getRole());
}
catch (Exception e) {
logger.warn("Error publishing OnRevoked event.", e);
}
}
}
}
}
/**
* Implementation of leadership context backed by Curator.
*/
private class CuratorContext implements Context {
CuratorContext() {
super();
}
@Override
public boolean isLeader() {
return LeaderInitiator.this.leaderSelector.hasLeadership();
}
@Override
public void yield() {
LeaderInitiator.this.leaderSelector.interruptLeadership();
}
@Override
public String toString() {
return "CuratorContext{role=" + LeaderInitiator.this.candidate.getRole() +
", id=" + LeaderInitiator.this.candidate.getId() +
", isLeader=" + isLeader() + "}";
}
}
}