危险的Hystrix线程池

    /*
     * ThreadPoolKey
     *
     * This defines which thread-pool this command should run on.
     *
     * It uses the HystrixThreadPoolKey if provided, then defaults to use HystrixCommandGroup.
     *
     * It can then be overridden by a property if defined so it can be changed at runtime.
     */
    private static HystrixThreadPoolKey initThreadPoolKey(HystrixThreadPoolKey threadPoolKey, HystrixCommandGroupKey groupKey, String threadPoolKeyOverride) {
        if (threadPoolKeyOverride == null) {
            // we don't have a property overriding the value so use either HystrixThreadPoolKey or HystrixCommandGroup
            if (threadPoolKey == null) {
                /* use HystrixCommandGroup if HystrixThreadPoolKey is null */
                return HystrixThreadPoolKey.Factory.asKey(groupKey.name());
            } else {
                return threadPoolKey;
            }
        } else {
            // we have a property defining the thread-pool so use it instead
            return HystrixThreadPoolKey.Factory.asKey(threadPoolKeyOverride);
        }
    }

    /*
     * Use the String from HystrixThreadPoolKey.name() instead of the HystrixThreadPoolKey instance as it's just an interface and we can't ensure the object
     * we receive implements hashcode/equals correctly and do not want the default hashcode/equals which would create a new threadpool for every object we get even if the name is the same
     */
    /* package */final static ConcurrentHashMap<String, HystrixThreadPool> threadPools = new ConcurrentHashMap<String, HystrixThreadPool>();

    /**
     * Get the {@link HystrixThreadPool} instance for a given {@link HystrixThreadPoolKey}.
     * <p>
     * This is thread-safe and ensures only 1 {@link HystrixThreadPool} per {@link HystrixThreadPoolKey}.
     *
     * @return {@link HystrixThreadPool} instance
     */
    /* package */static HystrixThreadPool getInstance(HystrixThreadPoolKey threadPoolKey, HystrixThreadPoolProperties.Setter propertiesBuilder) {
        // get the key to use instead of using the object itself so that if people forget to implement equals/hashcode things will still work
        String key = threadPoolKey.name();

        // this should find it for all but the first time
        HystrixThreadPool previouslyCached = threadPools.get(key);
        if (previouslyCached != null) {
            return previouslyCached;
        }

        // if we get here this is the first time so we need to initialize
        synchronized (HystrixThreadPool.class) {
            if (!threadPools.containsKey(key)) {
                threadPools.put(key, new HystrixThreadPoolDefault(threadPoolKey, propertiesBuilder));
            }
        }
        return threadPools.get(key);
    }

public class HystrixThreadPoolTest {

  public static void main(String[] args) throws InterruptedException {
    final int coreSize = 2, maximumSize = 5, maxQueueSize = 10;
    final String commandName = "TestThreadPoolCommand";

    final HystrixCommand.Setter commandConfig = HystrixCommand.Setter
        .withGroupKey(HystrixCommandGroupKey.Factory.asKey(commandName))
        .andCommandKey(HystrixCommandKey.Factory.asKey(commandName))
        .andCommandPropertiesDefaults(
            HystrixCommandProperties.Setter()
                .withExecutionTimeoutEnabled(false))
        .andThreadPoolPropertiesDefaults(
            HystrixThreadPoolProperties.Setter()
                .withCoreSize(coreSize)
                .withMaximumSize(maximumSize)
                .withAllowMaximumSizeToDivergeFromCoreSize(true)
                .withMaxQueueSize(maxQueueSize)
                .withQueueSizeRejectionThreshold(maxQueueSize));

    // Run command once, so we can get metrics.
    HystrixCommand<Void> command = new HystrixCommand<Void>(commandConfig) {
      @Override protected Void run() throws Exception {
        return null;
      }
    };
    command.execute();
    Thread.sleep(100);

    final CountDownLatch stopLatch = new CountDownLatch(1);
    List<Thread> threads = new ArrayList<Thread>();

    for (int i = 0; i < coreSize + maximumSize + maxQueueSize; i++) {
      final int fi = i + 1;

      Thread thread = new Thread(new Runnable() {
        public void run() {
          try {
            HystrixCommand<Void> command = new HystrixCommand<Void>(commandConfig) {
              @Override protected Void run() throws Exception {
                stopLatch.await();
                return null;
              }
            };
            command.execute();
          } catch (HystrixRuntimeException e) {
            System.out.println("Started Jobs: " + fi);
            System.out.println("Job:" + fi + " got rejected.");
            printThreadPoolStatus();
            System.out.println();
          }
        }
      });
      threads.add(thread);
      thread.start();
      Thread.sleep(200);

      if(fi == coreSize || fi == coreSize + maximumSize || fi == coreSize + maxQueueSize ) {
        System.out.println("Started Jobs: " + fi);
        printThreadPoolStatus();
        System.out.println();
      }
    }

    stopLatch.countDown();

    for (Thread thread : threads) {
      thread.join();
    }

  }

  static void printThreadPoolStatus() {
    for (HystrixThreadPoolMetrics threadPoolMetrics : HystrixThreadPoolMetrics.getInstances()) {
      String name = threadPoolMetrics.getThreadPoolKey().name();
      Number poolSize = threadPoolMetrics.getCurrentPoolSize();
      Number queueSize = threadPoolMetrics.getCurrentQueueSize();
      System.out.println("ThreadPoolKey: " + name + ", PoolSize: " + poolSize + ", QueueSize: " + queueSize);
    }

  }

}

// 任务数 = coreSize。此时coreSize个线程在工作
Started Jobs: 2
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 0

// 任务数 > coreSize。此时仍然只有coreSize个线程，多于coreSize的任务进入等候队列，没有创建新的线程  
Started Jobs: 7
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 5

// 任务数 = coreSize + maxQueueSize。此时仍然只有coreSize个线程，多于coreSize的任务进入等候队列，没有创建新的线程  
Started Jobs: 12
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 10

// 任务数 > coreSize + maxQueueSize。此时仍然只有coreSize个线程，等候队列已满，新增任务被拒绝 
Started Jobs: 13
Job:13 got rejected.
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 10

Started Jobs: 14
Job:14 got rejected.
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 10

Started Jobs: 15
Job:15 got rejected.
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 10

Started Jobs: 16
Job:16 got rejected.
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 10

Started Jobs: 17
Job:17 got rejected.
ThreadPoolKey: TestThreadPoolCommand, PoolSize: 2, QueueSize: 10

    /**
     * Creates a new {@code ThreadPoolExecutor} with the given initial
     * parameters.
     *
     * @param corePoolSize the number of threads to keep in the pool, even
     *        if they are idle, unless {@code allowCoreThreadTimeOut} is set
     * @param maximumPoolSize the maximum number of threads to allow in the
     *        pool
     * @param keepAliveTime when the number of threads is greater than
     *        the core, this is the maximum time that excess idle threads
     *        will wait for new tasks before terminating.
     * @param unit the time unit for the {@code keepAliveTime} argument
     * @param workQueue the queue to use for holding tasks before they are
     *        executed.  This queue will hold only the {@code Runnable}
     *        tasks submitted by the {@code execute} method.
     * @param threadFactory the factory to use when the executor
     *        creates a new thread
     * @param handler the handler to use when execution is blocked
     *        because the thread bounds and queue capacities are reached
     * @throws IllegalArgumentException if one of the following holds:<br>
     *         {@code corePoolSize < 0}<br>
     *         {@code keepAliveTime < 0}<br>
     *         {@code maximumPoolSize <= 0}<br>
     *         {@code maximumPoolSize < corePoolSize}
     * @throws NullPointerException if {@code workQueue}
     *         or {@code threadFactory} or {@code handler} is null
     */
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

    public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
        /*
         * Proceed in 3 steps:
         *
         * 1. If fewer than corePoolSize threads are running, try to
         * start a new thread with the given command as its first
         * task.  The call to addWorker atomically checks runState and
         * workerCount, and so prevents false alarms that would add
         * threads when it shouldn't, by returning false.
         *
         * 2. If a task can be successfully queued, then we still need
         * to double-check whether we should have added a thread
         * (because existing ones died since last checking) or that
         * the pool shut down since entry into this method. So we
         * recheck state and if necessary roll back the enqueuing if
         * stopped, or start a new thread if there are none.
         *
         * 3. If we cannot queue task, then we try to add a new
         * thread.  If it fails, we know we are shut down or saturated
         * and so reject the task.
         */
        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            reject(command);
    }

    public ThreadPoolExecutor getThreadPool(final HystrixThreadPoolKey threadPoolKey, HystrixThreadPoolProperties threadPoolProperties) {
        final ThreadFactory threadFactory = getThreadFactory(threadPoolKey);

        final boolean allowMaximumSizeToDivergeFromCoreSize = threadPoolProperties.getAllowMaximumSizeToDivergeFromCoreSize().get();
        final int dynamicCoreSize = threadPoolProperties.coreSize().get();
        final int keepAliveTime = threadPoolProperties.keepAliveTimeMinutes().get();
        final int maxQueueSize = threadPoolProperties.maxQueueSize().get();
        final BlockingQueue<Runnable> workQueue = getBlockingQueue(maxQueueSize);

        if (allowMaximumSizeToDivergeFromCoreSize) {
            final int dynamicMaximumSize = threadPoolProperties.maximumSize().get();
            if (dynamicCoreSize > dynamicMaximumSize) {
                logger.error("Hystrix ThreadPool configuration at startup for : " + threadPoolKey.name() + " is trying to set coreSize = " +
                        dynamicCoreSize + " and maximumSize = " + dynamicMaximumSize + ".  Maximum size will be set to " +
                        dynamicCoreSize + ", the coreSize value, since it must be equal to or greater than the coreSize value");
                return new ThreadPoolExecutor(dynamicCoreSize, dynamicCoreSize, keepAliveTime, TimeUnit.MINUTES, workQueue, threadFactory);
            } else {
                return new ThreadPoolExecutor(dynamicCoreSize, dynamicMaximumSize, keepAliveTime, TimeUnit.MINUTES, workQueue, threadFactory);
            }
        } else {
            return new ThreadPoolExecutor(dynamicCoreSize, dynamicCoreSize, keepAliveTime, TimeUnit.MINUTES, workQueue, threadFactory);
        }
    }

    public BlockingQueue<Runnable> getBlockingQueue(int maxQueueSize) {
        /*
         * We are using SynchronousQueue if maxQueueSize <= 0 (meaning a queue is not wanted).
         * <p>
         * SynchronousQueue will do a handoff from calling thread to worker thread and not allow queuing which is what we want.
         * <p>
         * Queuing results in added latency and would only occur when the thread-pool is full at which point there are latency issues
         * and rejecting is the preferred solution.
         */
        if (maxQueueSize <= 0) {
            return new SynchronousQueue<Runnable>();
        } else {
            return new LinkedBlockingQueue<Runnable>(maxQueueSize);
        }
    }

    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();
        }
    }

    public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
        if (threadPool != null) {
            if (!threadPool.isQueueSpaceAvailable()) {
                throw new RejectedExecutionException("Rejected command because thread-pool queueSize is at rejection threshold.");
            }
        }
        return worker.schedule(new HystrixContexSchedulerAction(concurrencyStrategy, action), delayTime, unit);
    }

coreSize = 2; maximumSize = 5; maxQueueSize = -1

coreSize = 2; maximumSize = 2; maxQueueSize = 10