ActiveMQ broker解析

在 ActiveMQ 中，broker 集中管理持久的、临时的 queue 和 topic。

public class BrokerFilter implements Broker {
    // 省略其他代码
    protected final Broker next;
}

最终的 Broker 链是这样的：

StatisticsBroker -> TransactionBroker -> CompositeDestinationBroker -> AdvisoryBroker -> ManagedRegionBroker

创建Broker 链：

// org.apache.activemq.broker.BrokerService
protected Broker createBroker() throws Exception {
    // 创建 RegionBroker
    regionBroker = createRegionBroker();
    // 添加拦截器
    Broker broker = addInterceptors(regionBroker);
    // Add a filter that will stop access to the broker once stopped
    broker = new MutableBrokerFilter(broker) {
        Broker old;

        @Override
        public void stop() throws Exception {
            old = this.next.getAndSet(new ErrorBroker("Broker has been stopped: " + this) {
                // Just ignore additional stop actions.
                @Override
                public void stop() throws Exception {
                }
            });
            old.stop();
        }

        @Override
        public void start() throws Exception {
            if (forceStart && old != null) {
                this.next.set(old);
            }
            getNext().start();
        }
    };
    return broker;
}

创建 RegionBroker：

protected Broker createRegionBroker(DestinationInterceptor destinationInterceptor) throws IOException {
    RegionBroker regionBroker;
    if (isUseJmx()) {
        try {
            regionBroker = new ManagedRegionBroker(this, getManagementContext(), getBrokerObjectName(),
                getTaskRunnerFactory(), getConsumerSystemUsage(), destinationFactory, destinationInterceptor,getScheduler(),getExecutor());
        } catch(MalformedObjectNameException me){
            LOG.warn("Cannot create ManagedRegionBroker due " + me.getMessage(), me);
            throw new IOException(me);
        }
    } else {
        regionBroker = new RegionBroker(this, getTaskRunnerFactory(), getConsumerSystemUsage(), destinationFactory,
                destinationInterceptor,getScheduler(),getExecutor());
    }
    destinationFactory.setRegionBroker(regionBroker);
    regionBroker.setKeepDurableSubsActive(keepDurableSubsActive);
    regionBroker.setBrokerName(getBrokerName());
    regionBroker.getDestinationStatistics().setEnabled(enableStatistics);
    regionBroker.setAllowTempAutoCreationOnSend(isAllowTempAutoCreationOnSend());
    if (brokerId != null) {
        regionBroker.setBrokerId(brokerId);
    }
    return regionBroker;
}

为RegionBroker添加BrokerFilter：

protected Broker addInterceptors(Broker broker) throws Exception {
    if (isSchedulerSupport()) {
        SchedulerBroker sb = new SchedulerBroker(this, broker, getJobSchedulerStore());
        if (isUseJmx()) {
            JobSchedulerViewMBean view = new JobSchedulerView(sb.getJobScheduler());
            try {
                ObjectName objectName = BrokerMBeanSupport.createJobSchedulerServiceName(getBrokerObjectName());
                AnnotatedMBean.registerMBean(getManagementContext(), view, objectName);
                this.adminView.setJMSJobScheduler(objectName);
            } catch (Throwable e) {
                throw IOExceptionSupport.create("JobScheduler could not be registered in JMX: "
                        + e.getMessage(), e);
            }
        }
        broker = sb;
    }
    if (isUseJmx()) {
        HealthViewMBean statusView = new HealthView((ManagedRegionBroker)getRegionBroker());
        try {
            ObjectName objectName = BrokerMBeanSupport.createHealthServiceName(getBrokerObjectName());
            AnnotatedMBean.registerMBean(getManagementContext(), statusView, objectName);
        } catch (Throwable e) {
            throw IOExceptionSupport.create("Status MBean could not be registered in JMX: "
                    + e.getMessage(), e);
        }
    }
    if (isAdvisorySupport()) {
        broker = new AdvisoryBroker(broker);
    }
    broker = new CompositeDestinationBroker(broker);
    broker = new TransactionBroker(broker, getPersistenceAdapter().createTransactionStore());
    if (isPopulateJMSXUserID()) {
        UserIDBroker userIDBroker = new UserIDBroker(broker);
        userIDBroker.setUseAuthenticatePrincipal(isUseAuthenticatedPrincipalForJMSXUserID());
        broker = userIDBroker;
    }
    if (isMonitorConnectionSplits()) {
        broker = new ConnectionSplitBroker(broker);
    }
    if (plugins != null) {
        for (int i = 0; i < plugins.length; i++) {
            BrokerPlugin plugin = plugins[i];
            broker = plugin.installPlugin(broker);
        }
    }
    return broker;
}

我们创建的topic和queue都记录在ManagedRegionBroker这个类中：

public class ManagedRegionBroker extends RegionBroker {
    private static final Logger LOG = LoggerFactory.getLogger(ManagedRegionBroker.class);
    private final ManagementContext managementContext;
    private final ObjectName brokerObjectName;
    private final Map<ObjectName, DestinationView> topics
        = new ConcurrentHashMap<ObjectName, DestinationView>();
    private final Map<ObjectName, DestinationView> queues
        = new ConcurrentHashMap<ObjectName, DestinationView>();
    private final Map<ObjectName, DestinationView> temporaryQueues
        = new ConcurrentHashMap<ObjectName, DestinationView>();
    private final Map<ObjectName, DestinationView> temporaryTopics
        = new ConcurrentHashMap<ObjectName, DestinationView>();
    private final Map<ObjectName, SubscriptionView> queueSubscribers
        = new ConcurrentHashMap<ObjectName, SubscriptionView>();
    private final Map<ObjectName, SubscriptionView> topicSubscribers
        = new ConcurrentHashMap<ObjectName, SubscriptionView>();
    private final Map<ObjectName, SubscriptionView> durableTopicSubscribers
        = new ConcurrentHashMap<ObjectName, SubscriptionView>();
    private final Map<ObjectName, SubscriptionView> inactiveDurableTopicSubscribers
        = new ConcurrentHashMap<ObjectName, SubscriptionView>();
    private final Map<ObjectName, SubscriptionView> temporaryQueueSubscribers
        = new ConcurrentHashMap<ObjectName, SubscriptionView>();
    private final Map<ObjectName, SubscriptionView> temporaryTopicSubscribers
        = new ConcurrentHashMap<ObjectName, SubscriptionView>();
    private final Map<ObjectName, ProducerView> queueProducers
        = new ConcurrentHashMap<ObjectName, ProducerView>();
    private final Map<ObjectName, ProducerView> topicProducers
        = new ConcurrentHashMap<ObjectName, ProducerView>();
    private final Map<ObjectName, ProducerView> temporaryQueueProducers
        = new ConcurrentHashMap<ObjectName, ProducerView>();
    private final Map<ObjectName, ProducerView> temporaryTopicProducers
        = new ConcurrentHashMap<ObjectName, ProducerView>();
    private final Map<ObjectName, ProducerView> dynamicDestinationProducers
        = new ConcurrentHashMap<ObjectName, ProducerView>();
    private final Map<SubscriptionKey, ObjectName> subscriptionKeys
        = new ConcurrentHashMap<SubscriptionKey, ObjectName>();
    private final Map<Subscription, ObjectName> subscriptionMap
        = new ConcurrentHashMap<Subscription, ObjectName>();
    private final Set<ObjectName> registeredMBeans
        = new CopyOnWriteArraySet<ObjectName>();
    /* This is the first broker in the broker interceptor chain. */
    private Broker contextBroker;
}