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本文主要研究一下HystrixThreadPool

HystrixThreadPool

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/HystrixThreadPool.java

/**
 * ThreadPool used to executed {@link HystrixCommand#run()} on separate threads when configured to do so with {@link HystrixCommandProperties#executionIsolationStrategy()}.
 * <p>
 * Typically each {@link HystrixCommandGroupKey} has its own thread-pool so that any one group of commands can not starve others from being able to run.
 * <p>
 * A {@link HystrixCommand} can be configured with a thread-pool explicitly by injecting a {@link HystrixThreadPoolKey} or via the
 * {@link HystrixCommandProperties#executionIsolationThreadPoolKeyOverride()} otherwise it
 * will derive a {@link HystrixThreadPoolKey} from the injected {@link HystrixCommandGroupKey}.
 * <p>
 * The pool should be sized large enough to handle normal healthy traffic but small enough that it will constrain concurrent execution if backend calls become latent.
 * <p>
 * For more information see the Github Wiki: https://github.com/Netflix/Hystrix/wiki/Configuration#wiki-ThreadPool and https://github.com/Netflix/Hystrix/wiki/How-it-Works#wiki-Isolation
 */
public interface HystrixThreadPool {

    /**
     * Implementation of {@link ThreadPoolExecutor}.
     *
     * @return ThreadPoolExecutor
     */
    public ExecutorService getExecutor();

    public Scheduler getScheduler();

    public Scheduler getScheduler(Func0<Boolean> shouldInterruptThread);

    /**
     * Mark when a thread begins executing a command.
     */
    public void markThreadExecution();

    /**
     * Mark when a thread completes executing a command.
     */
    public void markThreadCompletion();

    /**
     * Mark when a command gets rejected from the threadpool
     */
    public void markThreadRejection();

    /**
     * Whether the queue will allow adding an item to it.
     * <p>
     * This allows dynamic control of the max queueSize versus whatever the actual max queueSize is so that dynamic changes can be done via property changes rather than needing an app
     * restart to adjust when commands should be rejected from queuing up.
     *
     * @return boolean whether there is space on the queue
     */
    public boolean isQueueSpaceAvailable();

    //......
}

这个接口主要是定义getExecutor、getScheduler方法，以及一系列的mark方法(markThreadExecution、markThreadCompletion、markThreadRejection)

HystrixThreadPoolDefault

    /**
     * @ExcludeFromJavadoc
     * @ThreadSafe
     */
    /* package */static class HystrixThreadPoolDefault implements HystrixThreadPool {
        private static final Logger logger = LoggerFactory.getLogger(HystrixThreadPoolDefault.class);

        private final HystrixThreadPoolProperties properties;
        private final BlockingQueue<Runnable> queue;
        private final ThreadPoolExecutor threadPool;
        private final HystrixThreadPoolMetrics metrics;
        private final int queueSize;

        public HystrixThreadPoolDefault(HystrixThreadPoolKey threadPoolKey, HystrixThreadPoolProperties.Setter propertiesDefaults) {
            this.properties = HystrixPropertiesFactory.getThreadPoolProperties(threadPoolKey, propertiesDefaults);
            HystrixConcurrencyStrategy concurrencyStrategy = HystrixPlugins.getInstance().getConcurrencyStrategy();
            this.queueSize = properties.maxQueueSize().get();

            this.metrics = HystrixThreadPoolMetrics.getInstance(threadPoolKey,
                    concurrencyStrategy.getThreadPool(threadPoolKey, properties),
                    properties);
            this.threadPool = this.metrics.getThreadPool();
            this.queue = this.threadPool.getQueue();

            /* strategy: HystrixMetricsPublisherThreadPool */
            HystrixMetricsPublisherFactory.createOrRetrievePublisherForThreadPool(threadPoolKey, this.metrics, this.properties);
        }

        @Override
        public ThreadPoolExecutor getExecutor() {
            touchConfig();
            return threadPool;
        }

        @Override
        public Scheduler getScheduler() {
            //by default, interrupt underlying threads on timeout
            return getScheduler(new Func0<Boolean>() {
                @Override
                public Boolean call() {
                    return true;
                }
            });
        }

        @Override
        public Scheduler getScheduler(Func0<Boolean> shouldInterruptThread) {
            touchConfig();
            return new HystrixContextScheduler(HystrixPlugins.getInstance().getConcurrencyStrategy(), this, shouldInterruptThread);
        }

        // allow us to change things via fast-properties by setting it each time
        private void touchConfig() {
            final int dynamicCoreSize = properties.coreSize().get();
            final int configuredMaximumSize = properties.maximumSize().get();
            int dynamicMaximumSize = properties.actualMaximumSize();
            final boolean allowSizesToDiverge = properties.getAllowMaximumSizeToDivergeFromCoreSize().get();
            boolean maxTooLow = false;

            if (allowSizesToDiverge && configuredMaximumSize < dynamicCoreSize) {
                //if user sets maximum < core (or defaults get us there), we need to maintain invariant of core <= maximum
                dynamicMaximumSize = dynamicCoreSize;
                maxTooLow = true;
            }

            // In JDK 6, setCorePoolSize and setMaximumPoolSize will execute a lock operation. Avoid them if the pool size is not changed.
            if (threadPool.getCorePoolSize() != dynamicCoreSize || (allowSizesToDiverge && threadPool.getMaximumPoolSize() != dynamicMaximumSize)) {
                if (maxTooLow) {
                    logger.error("Hystrix ThreadPool configuration for : " + metrics.getThreadPoolKey().name() + " is trying to set coreSize = " +
                            dynamicCoreSize + " and maximumSize = " + configuredMaximumSize + ".  Maximum size will be set to " +
                            dynamicMaximumSize + ", the coreSize value, since it must be equal to or greater than the coreSize value");
                }
                threadPool.setCorePoolSize(dynamicCoreSize);
                threadPool.setMaximumPoolSize(dynamicMaximumSize);
            }

            threadPool.setKeepAliveTime(properties.keepAliveTimeMinutes().get(), TimeUnit.MINUTES);
        }

        @Override
        public void markThreadExecution() {
            metrics.markThreadExecution();
        }

        @Override
        public void markThreadCompletion() {
            metrics.markThreadCompletion();
        }

        @Override
        public void markThreadRejection() {
            metrics.markThreadRejection();
        }

        /**
         * Whether the threadpool queue has space available according to the <code>queueSizeRejectionThreshold</code> settings.
         *
         * Note that the <code>queueSize</code> is an final instance variable on HystrixThreadPoolDefault, and not looked up dynamically.
         * The data structure is static, so this does not make sense as a dynamic lookup.
         * The <code>queueSizeRejectionThreshold</code> can be dynamic (up to <code>queueSize</code>), so that should
         * still get checked on each invocation.
         * <p>
         * If a SynchronousQueue implementation is used (<code>maxQueueSize</code> <= 0), it always returns 0 as the size so this would always return true.
         */
        @Override
        public boolean isQueueSpaceAvailable() {
            if (queueSize <= 0) {
                // we don't have a queue so we won't look for space but instead
                // let the thread-pool reject or not
                return true;
            } else {
                return threadPool.getQueue().size() < properties.queueSizeRejectionThreshold().get();
            }
        }

    }

• getExecutor方法返回的是HystrixThreadPoolMetrics的ThreadPoolExecutor，只是每次get的时候会touch下config，刷新下threadPool的配置
• getScheduler方法这里用get不是太恰当，因为里头是new了一个HystrixContextScheduler
• mark方法主要是委托给HystrixThreadPoolMetrics

HystrixThreadPoolProperties

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/HystrixThreadPoolProperties.java

/**
 * Properties for instances of {@link HystrixThreadPool}.
 * <p>
 * Default implementation of methods uses Archaius (https://github.com/Netflix/archaius)
 *
 * Note a change in behavior in 1.5.7.  Prior to that version, the configuration for 'coreSize' was used to control
 * both coreSize and maximumSize.  This is a fixed-size threadpool that can never give up an unused thread.  In 1.5.7+,
 * the values can diverge, and if you set coreSize < maximumSize, threads can be given up (subject to the keep-alive
 * time)
 *
 * It is OK to leave maximumSize unset using any version of Hystrix.  If you do, then maximum size will default to
 * core size and you'll have a fixed-size threadpool.
 *
 * If you accidentally set maximumSize < coreSize, then maximum will be raised to coreSize
 * (this prioritizes keeping extra threads around rather than inducing threadpool rejections)
 */
public abstract class HystrixThreadPoolProperties {

    /* defaults */
    static int default_coreSize = 10;            // core size of thread pool
    static int default_maximumSize = 10;         // maximum size of thread pool
    static int default_keepAliveTimeMinutes = 1; // minutes to keep a thread alive
    static int default_maxQueueSize = -1;        // size of queue (this can't be dynamically changed so we use 'queueSizeRejectionThreshold' to artificially limit and reject)
                                                 // -1 turns it off and makes us use SynchronousQueue
    static boolean default_allow_maximum_size_to_diverge_from_core_size = false; //should the maximumSize config value get read and used in configuring the threadPool
                                                                                 //turning this on should be a conscious decision by the user, so we default it to false

    static int default_queueSizeRejectionThreshold = 5; // number of items in queue
    static int default_threadPoolRollingNumberStatisticalWindow = 10000; // milliseconds for rolling number
    static int default_threadPoolRollingNumberStatisticalWindowBuckets = 10; // number of buckets in rolling number (10 1-second buckets)

    private final HystrixProperty<Integer> corePoolSize;
    private final HystrixProperty<Integer> maximumPoolSize;
    private final HystrixProperty<Integer> keepAliveTime;
    private final HystrixProperty<Integer> maxQueueSize;
    private final HystrixProperty<Integer> queueSizeRejectionThreshold;
    private final HystrixProperty<Boolean> allowMaximumSizeToDivergeFromCoreSize;

    private final HystrixProperty<Integer> threadPoolRollingNumberStatisticalWindowInMilliseconds;
    private final HystrixProperty<Integer> threadPoolRollingNumberStatisticalWindowBuckets;
    //......
}

主要是配置corePoolSize、maximumPoolSize、keepAliveTime、maxQueueSize、queueSizeRejectionThreshold、allowMaximumSizeToDivergeFromCoreSize、threadPoolRollingNumberStatisticalWindowInMilliseconds、threadPoolRollingNumberStatisticalWindowBuckets

HystrixThreadPoolMetrics

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/HystrixThreadPoolMetrics.java

/**
 * Used by {@link HystrixThreadPool} to record metrics.
 */
public class HystrixThreadPoolMetrics extends HystrixMetrics {
    //......
    /**
     * Invoked each time a thread is executed.
     */
    public void markThreadExecution() {
        concurrentExecutionCount.incrementAndGet();
    }
    
    /**
     * Invoked each time a thread completes.
     */
    public void markThreadCompletion() {
        concurrentExecutionCount.decrementAndGet();
    }
    
    /**
     * Invoked each time a command is rejected from the thread-pool
     */
    public void markThreadRejection() {
        concurrentExecutionCount.decrementAndGet();
    }
    //......
}

这几个mark方法是相应的计数。

小结

HystrixThreadPool主要是定义getExecutor、getScheduler方法，以及一系列的mark方法。这些mark方法主要是做一些指标的count统计。

doc

• 16.10 How to Configure Hystrix Thread Pools