Spring Cloud Hystrix 源码解析(超过最大线程数、最大请求数)_hystirx动态修改线程数源码

之前分析了Spring Cloud Hystrix的创建和超时源码。

现在我们来分析下关于

Hystirx Thread模式，超过设置最大线程数量以及

Hystrix SEMAPHORE 模式，超过最大请求数量源码解析。

继续回到AbstractCommand的applyHystrixSemantics方法。

   private Observable<R> applyHystrixSemantics(final AbstractCommand<R> _cmd) {
        // mark that we're starting execution on the ExecutionHook
        // if this hook throws an exception, then a fast-fail occurs with no fallback.  No state is left inconsistent
        executionHook.onStart(_cmd);
 
        /* determine if we're allowed to execute */
        if (circuitBreaker.attemptExecution()) {
            final TryableSemaphore executionSemaphore = getExecutionSemaphore();
            final AtomicBoolean semaphoreHasBeenReleased = new AtomicBoolean(false);
            final Action0 singleSemaphoreRelease = new Action0() {
                @Override
                public void call() {
                    if (semaphoreHasBeenReleased.compareAndSet(false, true)) {
                        executionSemaphore.release();
                    }
                }
            };
 
            final Action1<Throwable> markExceptionThrown = new Action1<Throwable>() {
                @Override
                public void call(Throwable t) {
                    eventNotifier.markEvent(HystrixEventType.EXCEPTION_THROWN, commandKey);
                }
            };
 
            if (executionSemaphore.tryAcquire()) {
                try {
                    /* used to track userThreadExecutionTime */
                    executionResult = executionResult.setInvocationStartTime(System.currentTimeMillis());
                    return executeCommandAndObserve(_cmd)
                            .doOnError(markExceptionThrown)
                            .doOnTerminate(singleSemaphoreRelease)
                            .doOnUnsubscribe(singleSemaphoreRelease);
                } catch (RuntimeException e) {
                    return Observable.error(e);
                }
            } else {
                return handleSemaphoreRejectionViaFallback();
            }
        } else {
            return handleShortCircuitViaFallback();
        }
    }

首先我们看if (circuitBreaker.attemptExecution()) 代码。是判断熔断器是否可以执行请求。

        @Override
        public boolean attemptExecution() {
            if (properties.circuitBreakerForceOpen().get()) {
                return false;
            }
            if (properties.circuitBreakerForceClosed().get()) {
                return true;
            }
            if (circuitOpened.get() == -1) {
                return true;
            } else {
                if (isAfterSleepWindow()) {
                    if (status.compareAndSet(Status.OPEN, Status.HALF_OPEN)) {
                        //only the first request after sleep window should execute
                        return true;
                    } else {
                        return false;
                    }
                } else {
                    return false;
                }
            }
        }
        private boolean isAfterSleepWindow() {
            final long circuitOpenTime = circuitOpened.get();
            final long currentTime = System.currentTimeMillis();
            final long sleepWindowTime = properties.circuitBreakerSleepWindowInMilliseconds().get();
            return currentTime > circuitOpenTime + sleepWindowTime;
        }

如果熔断器开启，则直接返回false。否则会进行睡眠判断，当我们错误达到一定比例（默认50%）后，会开启熔断并设置一个熔断开启时间，之后根据我们设置的参数（默认是5s），当下次请求进来时，如果请求时间<上次熔断时间+睡眠时间，则直接返回false。

再看这一行final TryableSemaphore executionSemaphore = getExecutionSemaphore();通过getExecutionSemaphore方法获取executionSemaphore 对象。

    protected TryableSemaphore getExecutionSemaphore() {
        if (properties.executionIsolationStrategy().get() == ExecutionIsolationStrategy.SEMAPHORE) {
            if (executionSemaphoreOverride == null) {
                TryableSemaphore _s = executionSemaphorePerCircuit.get(commandKey.name());
                if (_s == null) {
                    // we didn't find one cache so setup
                    executionSemaphorePerCircuit.putIfAbsent(commandKey.name(), new TryableSemaphoreActual(properties.executionIsolationSemaphoreMaxConcurrentRequests()));
                    // assign whatever got set (this or another thread)
                    return executionSemaphorePerCircuit.get(commandKey.name());
                } else {
                    return _s;
                }
            } else {
                return executionSemaphoreOverride;
            }
        } else {
            // return NoOp implementation since we're not using SEMAPHORE isolation
            return TryableSemaphoreNoOp.DEFAULT;
        }
    }
 
static class TryableSemaphoreActual implements TryableSemaphore {
        protected final HystrixProperty<Integer> numberOfPermits;
        private final AtomicInteger count = new AtomicInteger(0);
 
        public TryableSemaphoreActual(HystrixProperty<Integer> numberOfPermits) {
            this.numberOfPermits = numberOfPermits;
        }
 
        @Override
        public boolean tryAcquire() {
            int currentCount = count.incrementAndGet();
            if (currentCount > numberOfPermits.get()) {
                count.decrementAndGet();
                return false;
            } else {
                return true;
            }
        }
}

先判断如果模式是SEMAPHORE ，则创建TryableSemaphoreActual，Thread模式则创建默认的。

继续往下

当请求判断进来后，会进入executionSemaphore.tryAcquire()方法，该方法有两个子类。根据我们设置的Hystrix模式不同，实现类不同。

Hystrix SEMAPHORE 模式

会进入刚才创建的TryableSemaphoreActual对象的tryAcquire方法。

 
static class TryableSemaphoreActual implements TryableSemaphore {
        protected final HystrixProperty<Integer> numberOfPermits;
        private final AtomicInteger count = new AtomicInteger(0);
 
        public TryableSemaphoreActual(HystrixProperty<Integer> numberOfPermits) {
            this.numberOfPermits = numberOfPermits;
        }
 
        @Override
        public boolean tryAcquire() {
            int currentCount = count.incrementAndGet();
            if (currentCount > numberOfPermits.get()) {
                count.decrementAndGet();
                return false;
            } else {
                return true;
            }
        }
}

该方法很简单，就是每次请求自增一个数，当数量大于我们设置的execution.isolation.semaphore.maxConcurrentRequests时，返回false，达到信号量控制。

Hystirx Thread模式

该模式对象是TryableSemaphoreNoOp，方法默认返回true。

static class TryableSemaphoreNoOp implements TryableSemaphore {
 
        public static final TryableSemaphore DEFAULT = new TryableSemaphoreNoOp();
 
        @Override
        public boolean tryAcquire() {
            return true;
        }
}

接着进入executeCommandAndObserve方法。该方法最后会进入到executeCommandWithSpecifiedIsolation方法。这里和之前文章分析的超时模式一致，都会进入到这里。

    private Observable<R> executeCommandWithSpecifiedIsolation(final AbstractCommand<R> _cmd) {
        if (properties.executionIsolationStrategy().get() == ExecutionIsolationStrategy.THREAD) {
            // mark that we are executing in a thread (even if we end up being rejected we still were a THREAD execution and not SEMAPHORE)
            return Observable.defer(new Func0<Observable<R>>() {
                @Override
                public Observable<R> call() {
                    executionResult = executionResult.setExecutionOccurred();
                    if (!commandState.compareAndSet(CommandState.OBSERVABLE_CHAIN_CREATED, CommandState.USER_CODE_EXECUTED)) {
                        return Observable.error(new IllegalStateException("execution attempted while in state : " + commandState.get().name()));
                    }
 
                    metrics.markCommandStart(commandKey, threadPoolKey, ExecutionIsolationStrategy.THREAD);
 
                    if (isCommandTimedOut.get() == TimedOutStatus.TIMED_OUT) {
                        // the command timed out in the wrapping thread so we will return immediately
                        // and not increment any of the counters below or other such logic
                        return Observable.error(new RuntimeException("timed out before executing run()"));
                    }
                    if (threadState.compareAndSet(ThreadState.NOT_USING_THREAD, ThreadState.STARTED)) {
                        //we have not been unsubscribed, so should proceed
                        HystrixCounters.incrementGlobalConcurrentThreads();
                        threadPool.markThreadExecution();
                        // store the command that is being run
                        endCurrentThreadExecutingCommand = Hystrix.startCurrentThreadExecutingCommand(getCommandKey());
                        executionResult = executionResult.setExecutedInThread();
                        /**
                         * If any of these hooks throw an exception, then it appears as if the actual execution threw an error
                         */
                        try {
                            executionHook.onThreadStart(_cmd);
                            executionHook.onRunStart(_cmd);
                            executionHook.onExecutionStart(_cmd);
                            return getUserExecutionObservable(_cmd);
                        } catch (Throwable ex) {
                            return Observable.error(ex);
                        }
                    } else {
                        //command has already been unsubscribed, so return immediately
                        return Observable.error(new RuntimeException("unsubscribed before executing run()"));
                    }
                }
            }).doOnTerminate(new Action0() {
                @Override
                public void call() {
                    if (threadState.compareAndSet(ThreadState.STARTED, ThreadState.TERMINAL)) {
                        handleThreadEnd(_cmd);
                    }
                    if (threadState.compareAndSet(ThreadState.NOT_USING_THREAD, ThreadState.TERMINAL)) {
                        //if it was never started and received terminal, then no need to clean up (I don't think this is possible)
                    }
                    //if it was unsubscribed, then other cleanup handled it
                }
            }).doOnUnsubscribe(new Action0() {
                @Override
                public void call() {
                    if (threadState.compareAndSet(ThreadState.STARTED, ThreadState.UNSUBSCRIBED)) {
                        handleThreadEnd(_cmd);
                    }
                    if (threadState.compareAndSet(ThreadState.NOT_USING_THREAD, ThreadState.UNSUBSCRIBED)) {
                        //if it was never started and was cancelled, then no need to clean up
                    }
                    //if it was terminal, then other cleanup handled it
                }
            }).subscribeOn(threadPool.getScheduler(new Func0<Boolean>() {
                @Override
                public Boolean call() {
                    return properties.executionIsolationThreadInterruptOnTimeout().get() && _cmd.isCommandTimedOut.get() == TimedOutStatus.TIMED_OUT;
                }
            }));

还是和之前一样，创建了RxJava的事件的流，我们看最后这句subscribeOn，表示这些执行是异步线程执行。看一下getScheduler方法。

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

再看一下subscribeOn方法。

    public final Observable<T> subscribeOn(Scheduler scheduler) {
        if (this instanceof ScalarSynchronousObservable) {
            return ((ScalarSynchronousObservable<T>)this).scalarScheduleOn(scheduler);
        }
        return create(new OperatorSubscribeOn<T>(this, scheduler));
    }
 
   public OperatorSubscribeOn(Observable<T> source, Scheduler scheduler) {
        this.scheduler = scheduler;
        this.source = source;
    }
 
    @Override
    public void call(final Subscriber<? super T> subscriber) {
        final Worker inner = scheduler.createWorker();
        subscriber.add(inner);
 
        inner.schedule(new Action0() {
            @Override
            public void call() {
                final Thread t = Thread.currentThread();
 
                Subscriber<T> s = new Subscriber<T>(subscriber) {
                    @Override
                    public void onNext(T t) {
                        subscriber.onNext(t);
                    }
 
                    @Override
                    public void onError(Throwable e) {
                        try {
                            subscriber.onError(e);
                        } finally {
                            inner.unsubscribe();
                        }
                    }
 
                    @Override
                    public void onCompleted() {
                        try {
                            subscriber.onCompleted();
                        } finally {
                            inner.unsubscribe();
                        }
                    }
 
                    @Override
                    public void setProducer(final Producer p) {
                        subscriber.setProducer(new Producer() {
                            @Override
                            public void request(final long n) {
                                if (t == Thread.currentThread()) {
                                    p.request(n);
                                } else {
                                    inner.schedule(new Action0() {
                                        @Override
                                        public void call() {
                                            p.request(n);
                                        }
                                    });
                                }
                            }
                        });
                    }
                };
 
                source.unsafeSubscribe(s);
            }
        });
    }

最后会执行HystrixContextScheduler类中的内部类ThreadPoolWorker的schedule方法。

       public Subscription schedule(final Action0 action) {
            if (subscription.isUnsubscribed()) {
                // don't schedule, we are unsubscribed
                return Subscriptions.unsubscribed();
            }
 
            // This is internal RxJava API but it is too useful.
            ScheduledAction sa = new ScheduledAction(action);
 
            subscription.add(sa);
            sa.addParent(subscription);
 
            ThreadPoolExecutor executor = (ThreadPoolExecutor) threadPool.getExecutor();
            FutureTask<?> f = (FutureTask<?>) executor.submit(sa);
            sa.add(new FutureCompleterWithConfigurableInterrupt(f, shouldInterruptThread, executor));
 
            return sa;
        }

从方法中我们可以看到，当执行executor.submit时调用的是Java的ThreadPoolExecutor的submit方法，如果超过了设置的最大队列，则直接拒绝。

这里的队列设置在HystrixCommandAspect创建AbstractCommand时确定

    protected AbstractCommand(HystrixCommandGroupKey group, HystrixCommandKey key, HystrixThreadPoolKey threadPoolKey, HystrixCircuitBreaker circuitBreaker, HystrixThreadPool threadPool,
            HystrixCommandProperties.Setter commandPropertiesDefaults, HystrixThreadPoolProperties.Setter threadPoolPropertiesDefaults,
            HystrixCommandMetrics metrics, TryableSemaphore fallbackSemaphore, TryableSemaphore executionSemaphore,
            HystrixPropertiesStrategy propertiesStrategy, HystrixCommandExecutionHook executionHook) {
 
        this.commandGroup = initGroupKey(group);
        this.commandKey = initCommandKey(key, getClass());
        this.properties = initCommandProperties(this.commandKey, propertiesStrategy, commandPropertiesDefaults);
        this.threadPoolKey = initThreadPoolKey(threadPoolKey, this.commandGroup, this.properties.executionIsolationThreadPoolKeyOverride().get());
        this.metrics = initMetrics(metrics, this.commandGroup, this.threadPoolKey, this.commandKey, this.properties);
        this.circuitBreaker = initCircuitBreaker(this.properties.circuitBreakerEnabled().get(), circuitBreaker, this.commandGroup, this.commandKey, this.properties, this.metrics);
        this.threadPool = initThreadPool(threadPool, this.threadPoolKey, threadPoolPropertiesDefaults);
        ....................
}

    private static HystrixThreadPool initThreadPool(HystrixThreadPool fromConstructor, HystrixThreadPoolKey threadPoolKey, HystrixThreadPoolProperties.Setter threadPoolPropertiesDefaults) {
        if (fromConstructor == null) {
            // get the default implementation of HystrixThreadPool
            return HystrixThreadPool.Factory.getInstance(threadPoolKey, threadPoolPropertiesDefaults);
        } else {
            return fromConstructor;
        }
    }
 
    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);
        }

最后会创建HystrixThreadPoolDefault对象。

        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,
                    //此处创建线程池
                    concurrencyStrategy.getThreadPool(threadPoolKey, properties),
                    properties);
            this.threadPool = this.metrics.getThreadPool();
            this.queue = this.threadPool.getQueue();
 
            /* strategy: HystrixMetricsPublisherThreadPool */
            HystrixMetricsPublisherFactory.createOrRetrievePublisherForThreadPool(threadPoolKey, this.metrics, this.properties);
        }
 
        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) {
        if (maxQueueSize <= 0) {
            return new SynchronousQueue<Runnable>();
        } else {
            return new LinkedBlockingQueue<Runnable>(maxQueueSize);
        }
    }

可以看到如果我们不设置maxQueueSize（默认-1）这个参数，是会创建SynchronousQueue对象。

如果设置了最大请求数，则会创建LinkedBlockingQueue队列。

常用设置：

@HystrixCommand(threadPoolProperties = {@HystrixProperty(name = "coreSize",value = "2"),
        @HystrixProperty(name = "allowMaximumSizeToDivergeFromCoreSize",value="true"),
        @HystrixProperty(name = "maximumSize",value="3"),
        @HystrixProperty(name = "maxQueueSize",value="2")},
        commandProperties = {@HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "10000")}
        ,fallbackMethod = "fallback")