聊聊dubbo的EagerThreadPool

序

本文主要研究一下 dubbo 的 EagerThreadPool

EagerThreadPool

dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/threadpool/support/eager/EagerThreadPool.java

public class EagerThreadPool implements ThreadPool {

    @Override
    public Executor getExecutor(URL url) {String name = url.getParameter(THREAD_NAME_KEY, DEFAULT_THREAD_NAME);
        int cores = url.getParameter(CORE_THREADS_KEY, DEFAULT_CORE_THREADS);
        int threads = url.getParameter(THREADS_KEY, Integer.MAX_VALUE);
        int queues = url.getParameter(QUEUES_KEY, DEFAULT_QUEUES);
        int alive = url.getParameter(ALIVE_KEY, DEFAULT_ALIVE);

        // init queue and executor
        TaskQueue<Runnable> taskQueue = new TaskQueue<Runnable>(queues <= 0 ? 1 : queues);
        EagerThreadPoolExecutor executor = new EagerThreadPoolExecutor(cores,
                threads,
                alive,
                TimeUnit.MILLISECONDS,
                taskQueue,
                new NamedInternalThreadFactory(name, true),
                new AbortPolicyWithReport(name, url));
        taskQueue.setExecutor(executor);
        return executor;
    }
}

• EagerThreadPool 实现了 ThreadPool 接口，其 getExecutor 创建的是 EagerThreadPoolExecutor，它使用的 queue 为 TaskQueue，使用的 threadFactory 为 NamedInternalThreadFactory，使用的 rejectedExecutionHandler 为 AbortPolicyWithReport

EagerThreadPoolExecutor

dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/threadpool/support/eager/EagerThreadPoolExecutor.java

public class EagerThreadPoolExecutor extends ThreadPoolExecutor {

    /**
     * task count
     */
    private final AtomicInteger submittedTaskCount = new AtomicInteger(0);

    public EagerThreadPoolExecutor(int corePoolSize,
                                   int maximumPoolSize,
                                   long keepAliveTime,
                                   TimeUnit unit, TaskQueue<Runnable> workQueue,
                                   ThreadFactory threadFactory,
                                   RejectedExecutionHandler handler) {super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);
    }

    /**
     * @return current tasks which are executed
     */
    public int getSubmittedTaskCount() {return submittedTaskCount.get();
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {submittedTaskCount.decrementAndGet();
    }

    @Override
    public void execute(Runnable command) {if (command == null) {throw new NullPointerException();
        }
        // do not increment in method beforeExecute!
        submittedTaskCount.incrementAndGet();
        try {super.execute(command);
        } catch (RejectedExecutionException rx) {
            // retry to offer the task into queue.
            final TaskQueue queue = (TaskQueue) super.getQueue();
            try {if (!queue.retryOffer(command, 0, TimeUnit.MILLISECONDS)) {submittedTaskCount.decrementAndGet();
                    throw new RejectedExecutionException("Queue capacity is full.", rx);
                }
            } catch (InterruptedException x) {submittedTaskCount.decrementAndGet();
                throw new RejectedExecutionException(x);
            }
        } catch (Throwable t) {
            // decrease any way
            submittedTaskCount.decrementAndGet();
            throw t;
        }
    }
}

• EagerThreadPoolExecutor 继承了 ThreadPoolExecutor，它维护了 submittedTaskCount，在执行任务之前递增，在 afterExecute 的时候胡递减；其 execute 方法会捕获 RejectedExecutionException，然后使用 TaskQueue 的 retryOffer 再重新入队，入队不成功才抛出 RejectedExecutionException

TaskQueue

dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/threadpool/support/eager/TaskQueue.java

public class TaskQueue<R extends Runnable> extends LinkedBlockingQueue<Runnable> {

    private static final long serialVersionUID = -2635853580887179627L;

    private EagerThreadPoolExecutor executor;

    public TaskQueue(int capacity) {super(capacity);
    }

    public void setExecutor(EagerThreadPoolExecutor exec) {executor = exec;}

    @Override
    public boolean offer(Runnable runnable) {if (executor == null) {throw new RejectedExecutionException("The task queue does not have executor!");
        }

        int currentPoolThreadSize = executor.getPoolSize();
        // have free worker. put task into queue to let the worker deal with task.
        if (executor.getSubmittedTaskCount() < currentPoolThreadSize) {return super.offer(runnable);
        }

        // return false to let executor create new worker.
        if (currentPoolThreadSize < executor.getMaximumPoolSize()) {return false;}

        // currentPoolThreadSize >= max
        return super.offer(runnable);
    }

    /**
     * retry offer task
     *
     * @param o task
     * @return offer success or not
     * @throws RejectedExecutionException if executor is terminated.
     */
    public boolean retryOffer(Runnable o, long timeout, TimeUnit unit) throws InterruptedException {if (executor.isShutdown()) {throw new RejectedExecutionException("Executor is shutdown!");
        }
        return super.offer(o, timeout, unit);
    }
}

• TaskQueue 继承了 LinkedBlockingQueue，它覆盖了 offer 方法，该方法在 submittedTaskCount 小于 poolSize 的时候会入队，如果大于等于 poolSize 则再判断 currentPoolThreadSize 是否小于 maximumPoolSize，如果小于则返回 false 让线程池创建新线程，最后在 currentPoolThreadSize 大于等于 maximumPoolSize 的时候入队

NamedInternalThreadFactory

dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/threadlocal/NamedInternalThreadFactory.java

public class NamedInternalThreadFactory extends NamedThreadFactory {public NamedInternalThreadFactory() {super();
    }

    public NamedInternalThreadFactory(String prefix) {super(prefix, false);
    }

    public NamedInternalThreadFactory(String prefix, boolean daemon) {super(prefix, daemon);
    }

    @Override
    public Thread newThread(Runnable runnable) {String name = mPrefix + mThreadNum.getAndIncrement();
        InternalThread ret = new InternalThread(mGroup, runnable, name, 0);
        ret.setDaemon(mDaemon);
        return ret;
    }
}

• NamedInternalThreadFactory 继承了 NamedThreadFactory，这里创建的是 InternalThread

AbortPolicyWithReport

dubbo-2.7.2/dubbo-common/src/main/java/org/apache/dubbo/common/threadpool/support/AbortPolicyWithReport.java

public class AbortPolicyWithReport extends ThreadPoolExecutor.AbortPolicy {protected static final Logger logger = LoggerFactory.getLogger(AbortPolicyWithReport.class);

    private final String threadName;

    private final URL url;

    private static volatile long lastPrintTime = 0;

    private static final long TEN_MINUTES_MILLS = 10 * 60 * 1000;

    private static final String OS_WIN_PREFIX = "win";

    private static final String OS_NAME_KEY = "os.name";

    private static final String WIN_DATETIME_FORMAT = "yyyy-MM-dd_HH-mm-ss";

    private static final String DEFAULT_DATETIME_FORMAT = "yyyy-MM-dd_HH:mm:ss";

    private static Semaphore guard = new Semaphore(1);

    public AbortPolicyWithReport(String threadName, URL url) {
        this.threadName = threadName;
        this.url = url;
    }

    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        String msg = String.format("Thread pool is EXHAUSTED!" +
                "Thread Name: %s, Pool Size: %d (active: %d, core: %d, max: %d, largest: %d), Task: %d (completed:"
                + "%d)," +
                "Executor status:(isShutdown:%s, isTerminated:%s, isTerminating:%s), in %s://%s:%d!",
            threadName, e.getPoolSize(), e.getActiveCount(), e.getCorePoolSize(), e.getMaximumPoolSize(),
            e.getLargestPoolSize(),
            e.getTaskCount(), e.getCompletedTaskCount(), e.isShutdown(), e.isTerminated(), e.isTerminating(),
            url.getProtocol(), url.getIp(), url.getPort());
        logger.warn(msg);
        dumpJStack();
        throw new RejectedExecutionException(msg);
    }

    private void dumpJStack() {long now = System.currentTimeMillis();

        //dump every 10 minutes
        if (now - lastPrintTime < TEN_MINUTES_MILLS) {return;}

        if (!guard.tryAcquire()) {return;}

        ExecutorService pool = Executors.newSingleThreadExecutor();
        pool.execute(() -> {String dumpPath = url.getParameter(DUMP_DIRECTORY, System.getProperty("user.home"));

            SimpleDateFormat sdf;

            String os = System.getProperty(OS_NAME_KEY).toLowerCase();

            // window system don't support":" in file name
            if (os.contains(OS_WIN_PREFIX)) {sdf = new SimpleDateFormat(WIN_DATETIME_FORMAT);
            } else {sdf = new SimpleDateFormat(DEFAULT_DATETIME_FORMAT);
            }

            String dateStr = sdf.format(new Date());
            //try-with-resources
            try (FileOutputStream jStackStream = new FileOutputStream(new File(dumpPath, "Dubbo_JStack.log" + "." + dateStr))) {JVMUtil.jstack(jStackStream);
            } catch (Throwable t) {logger.error("dump jStack error", t);
            } finally {guard.release();
            }
            lastPrintTime = System.currentTimeMillis();});
        //must shutdown thread pool ,if not will lead to OOM
        pool.shutdown();}

}

• AbortPolicyWithReport 继承了 ThreadPoolExecutor.AbortPolicy，其 rejectedExecution 方法会输出包含 thread pool 相关信息的 msg，然后使用 warn 级别打印出来，然后进行 dumpJStack，最后再抛出 RejectedExecutionException

小结

EagerThreadPool 实现了 ThreadPool 接口，其 getExecutor 创建的是 EagerThreadPoolExecutor，它使用的 queue 为 TaskQueue，使用的 threadFactory 为 NamedInternalThreadFactory，使用的 rejectedExecutionHandler 为 AbortPolicyWithReport

doc

• EagerThreadPool