INT-4058: Add leader initiator for lock registry
JIRA: https://jira.spring.io/browse/INT-4058 If you hold the lock, you are the leader. This simple idea gets you a long way if there is no "native" leader initiator. E.g. you can use this with a RDBMS with JdbcLockRegistry. Add some docs on leader election under "endpoints" Make thread name for leader initiator unique In case there are multiple instances in the same context we would like to be able to spot them in the logs. INT-4058: Polishing * Code refactoring in the `LockRegistryLeaderInitiator`: SI use 120 line length * Add `Assert.notNull()` for required properties * Add `this.lock.unlock()` and `Thread.sleep(LockRegistryLeaderInitiator.this.busyWaitMillis)` into the `catch` block to let distributed elections to work. Otherwise there is a big chance that we will acquire the lock and become a leader again just after `yield()` * Change `LockContext.toString()` to use simple `String` concatenation which is optimized by compiler to the `StringBuilder`. That let to have some better micro-performance compared with with extra `Formatter` object in case of `String.format()` * Add `JdbcLockRegistryLeaderInitiatorTests` * Fix `yield()` logic based on the `Future.cancel(true)`. Since one `FutureTask.cancel(true)` makes it as `INTERRUPTED` any subsequent `yield()` does not make any effect, therefore our infinite selector loop isn't interrupted one more time. * Reschedule the `LeaderSelector` in the `yield()` after cancel(true). * Rework `catch` in the selector loop just to the `InterruptedException` and `return null;` to stop looping and let reschedule the selector. * Add one more `onRevoked` logic into the `final` of the selector loop to notify that we have lost leadership during `stop()` * Improve `JdbcLockRegistryLeaderInitiatorTests` to ensure that several `yield()` on the same initiator work well. * Add `What's New` note.
This commit is contained in:
Dave Syer
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/*
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* Copyright 2016 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.integration.jdbc.leader;
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import static org.hamcrest.Matchers.is;
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import static org.junit.Assert.assertNotNull;
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import static org.junit.Assert.assertThat;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.TimeUnit;
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import org.junit.AfterClass;
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import org.junit.BeforeClass;
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import org.junit.Test;
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import org.springframework.integration.jdbc.lock.DefaultLockRepository;
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import org.springframework.integration.jdbc.lock.JdbcLockRegistry;
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import org.springframework.integration.leader.Context;
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import org.springframework.integration.leader.DefaultCandidate;
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import org.springframework.integration.leader.event.LeaderEventPublisher;
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import org.springframework.integration.support.leader.LockRegistryLeaderInitiator;
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import org.springframework.jdbc.datasource.embedded.EmbeddedDatabase;
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import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
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import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType;
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/**
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* @author Artem Bilan
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* @since 4.3.1
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*/
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public class JdbcLockRegistryLeaderInitiatorTests {
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public static EmbeddedDatabase dataSource;
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@BeforeClass
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public static void init() {
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dataSource = new EmbeddedDatabaseBuilder()
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.setType(EmbeddedDatabaseType.H2)
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.addScript("classpath:/org/springframework/integration/jdbc/schema-h2.sql")
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.build();
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}
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@AfterClass
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public static void destroy() {
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dataSource.shutdown();
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}
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@Test
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public void testDistributedLeaderElection() throws Exception {
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CountDownLatch granted = new CountDownLatch(1);
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CountingPublisher countingPublisher = new CountingPublisher(granted);
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List<LockRegistryLeaderInitiator> initiators = new ArrayList<LockRegistryLeaderInitiator>();
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for (int i = 0; i < 2; i++) {
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DefaultLockRepository lockRepository = new DefaultLockRepository(dataSource);
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lockRepository.afterPropertiesSet();
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LockRegistryLeaderInitiator initiator = new LockRegistryLeaderInitiator(
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new JdbcLockRegistry(lockRepository),
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new DefaultCandidate("foo", "bar"));
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initiator.setLeaderEventPublisher(countingPublisher);
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initiators.add(initiator);
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}
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for (LockRegistryLeaderInitiator initiator : initiators) {
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initiator.start();
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}
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assertThat(granted.await(10, TimeUnit.SECONDS), is(true));
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LockRegistryLeaderInitiator initiator1 = countingPublisher.initiator;
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LockRegistryLeaderInitiator initiator2 = null;
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for (LockRegistryLeaderInitiator initiator : initiators) {
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if (initiator != initiator1) {
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initiator2 = initiator;
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break;
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}
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}
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assertNotNull(initiator2);
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assertThat(initiator1.getContext().isLeader(), is(true));
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assertThat(initiator2.getContext().isLeader(), is(false));
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final CountDownLatch granted1 = new CountDownLatch(1);
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final CountDownLatch granted2 = new CountDownLatch(1);
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CountDownLatch revoked1 = new CountDownLatch(1);
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CountDownLatch revoked2 = new CountDownLatch(1);
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initiator1.setLeaderEventPublisher(new CountingPublisher(granted1, revoked1) {
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@Override
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public void publishOnRevoked(Object source, Context context, String role) {
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try {
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// It's difficult to see round-robin election, so block one initiator until the second is elected.
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assertThat(granted2.await(10, TimeUnit.SECONDS), is(true));
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}
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catch (InterruptedException e) {
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// No op
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}
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super.publishOnRevoked(source, context, role);
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}
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});
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initiator2.setLeaderEventPublisher(new CountingPublisher(granted2, revoked2) {
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@Override
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public void publishOnRevoked(Object source, Context context, String role) {
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try {
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// It's difficult to see round-robin election, so block one initiator until the second is elected.
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assertThat(granted1.await(10, TimeUnit.SECONDS), is(true));
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}
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catch (InterruptedException e) {
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// No op
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}
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super.publishOnRevoked(source, context, role);
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}
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});
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initiator1.getContext().yield();
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assertThat(revoked1.await(10, TimeUnit.SECONDS), is(true));
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assertThat(initiator2.getContext().isLeader(), is(true));
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assertThat(initiator1.getContext().isLeader(), is(false));
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initiator2.getContext().yield();
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assertThat(revoked2.await(10, TimeUnit.SECONDS), is(true));
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assertThat(initiator1.getContext().isLeader(), is(true));
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assertThat(initiator2.getContext().isLeader(), is(false));
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initiator2.stop();
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CountDownLatch revoked11 = new CountDownLatch(1);
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initiator1.setLeaderEventPublisher(new CountingPublisher(new CountDownLatch(1), revoked11));
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initiator1.getContext().yield();
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assertThat(revoked11.await(10, TimeUnit.SECONDS), is(true));
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assertThat(initiator1.getContext().isLeader(), is(false));
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initiator1.stop();
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}
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private static class CountingPublisher implements LeaderEventPublisher {
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private CountDownLatch granted;
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private CountDownLatch revoked;
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private volatile LockRegistryLeaderInitiator initiator;
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CountingPublisher(CountDownLatch granted, CountDownLatch revoked) {
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this.granted = granted;
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this.revoked = revoked;
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}
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CountingPublisher(CountDownLatch granted) {
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this(granted, new CountDownLatch(1));
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}
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@Override
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public void publishOnRevoked(Object source, Context context, String role) {
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this.revoked.countDown();
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}
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@Override
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public void publishOnGranted(Object source, Context context, String role) {
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this.initiator = (LockRegistryLeaderInitiator) source;
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this.granted.countDown();
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}
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}
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}
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