moquette改造笔记(三)：优化BrokerInterceptor 中的线程池

摘要：修改的实现，实现接口在改造笔记一整合到中修改实现，添加对的实现如下负载过大，处理不过来时，会回调该方法例如可以发生邮件通知相关人员改造笔记四解决中的调用两次

在io.moquette.spi.impl.BrokerInterceptor的构造函数中，新建了一个线程池，代码如下：

private BrokerInterceptor(int poolSize, List handlers) {
        LOG.info("Initializing broker interceptor. InterceptorIds={}", getInterceptorIds(handlers));
        this.handlers = new HashMap<>();
        for (Class messageType : InterceptHandler.ALL_MESSAGE_TYPES) {
            this.handlers.put(messageType, new CopyOnWriteArrayList());
        }
        for (InterceptHandler handler : handlers) {
            this.addInterceptHandler(handler);
        }
        executor = Executors.newFixedThreadPool(poolSize);
    }

executor = Executors.newFixedThreadPool(poolSize);这句代码虽然创建了一个固定线程数量的线程池，但是线程池的任务队列并没有做限制，一旦某个InterceptHandler中的某个方法进行了耗时处理，在高并发的情况下，会很容易导致线程池的队列堆积大量待处理的任务，进而可能造成内存溢出。

分别添加以下类和接口

public class ThreadPoolHelper {
    public static ExecutorService createFixedExecutor(int threadNum,int capacity,String threadFactoryName) {
        return new ThreadPoolExecutor(
                threadNum,
                threadNum,
                30,
                TimeUnit.SECONDS,
                new LinkedBlockingDeque(capacity),
                new SimpleThreadFactory(threadFactoryName),
                new LogDiscardRejectPolicy()
        );
    }
}

public class SimpleThreadFactory implements ThreadFactory {
    private static final String NAME_FORMAT = "%s-%s";
    private String threadNamePrefix;

    public SimpleThreadFactory(String threadNamePrefix) {
        this.threadNamePrefix = threadNamePrefix;
    }

    @Override
    public Thread newThread(Runnable runnable) {
        Thread thread = new Thread(runnable);
        thread.setName(String.format(NAME_FORMAT, threadNamePrefix, System.currentTimeMillis()));
        return thread;
    }
}


public class LogDiscardRejectPolicy implements RejectedExecutionHandler {
    private static final Logger LOG = LoggerFactory.getLogger(LogDiscardRejectPolicy.class);

    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        LOG.error("executor:{} task queue has full, runnable:{} discarded",executor,r);
        if (!(r instanceof PublishTask)) {
            return;
        }

        PublishTask publishTask = (PublishTask) r;
        InterceptHandler interceptHandler = publishTask.getInterceptHandler();
        if (!(interceptHandler instanceof RejectHandler)) {
            return;
        }

        ((RejectHandler)interceptHandler).rejectedExecution(r,executor);
    }
}


public interface RejectHandler {
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor);
}

BrokerInterceptor 创建线程池的逻辑改为

private BrokerInterceptor(int poolSize, int capacity, List handlers) {
        LOG.info("Initializing broker interceptor. InterceptorIds={}", getInterceptorIds(handlers));
        this.handlers = new HashMap<>();
        for (Class messageType : InterceptHandler.ALL_MESSAGE_TYPES) {
            this.handlers.put(messageType, new CopyOnWriteArrayList());
        }
        for (InterceptHandler handler : handlers) {
            this.addInterceptHandler(handler);
        }

        /** modify by liuhh */
        executor = ThreadPoolHelper.createFixedExecutor(poolSize, capacity, THREAD_POOL_NAME);
        //executor = Executors.newFixedThreadPool(poolSize);

    }

解释：
（1）ThreadPoolHelper中的createFixedExecutor()方法为新建的线程池指定任务队列大小和拒绝策略LogDiscardRejectPolicy
（2）在LogDiscardRejectPolicy中，首先将被拒绝的任务log一遍，对于PublishTask（moquette改造笔记(二)：优化BrokerInterceptor notifyTopicPublished()逻辑）做特殊处理，会交给实现RejectHandler的InterceptHandler处理，由业务逻辑决定，出现任务太多处理不完被遗弃的任务该如何处理。

在 moquette改造笔记(一)：整合到SpringBoot 中修改SafetyInterceptHandler实现，添加对RejectHandler的实现如下

@Slf4j
@Component
public class SafetyInterceptHandler extends AbstractInterceptHandler{

    @Override
    public String getID() {
        return SafetyInterceptHandler.class.getName();
    }

    @Override
    public void onConnect(InterceptConnectMessage msg) {
        
    }

    @Override
    public void onConnectionLost(InterceptConnectionLostMessage msg) {
       
    }


    @Override
    public void onPublish(InterceptPublishMessage msg) {
       
    }


    @Override
    public void onMessageAcknowledged(InterceptAcknowledgedMessage msg) {
        
    }
    
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        /**MQTT SERVICE 负载过大，处理不过来时，会回调该方法*/
        //例如可以发生邮件通知相关人员
    }

}

moquette改造笔记(四)：解决InterceptHandler中的onConnectionLost()调用两次