BUG背景

JDK: 11.0.4
Spring Cloud Finchley.SR3

相关配置：

#开启hystrix
feign.hystrix.enabled=true
#关闭断路器
hystrix.command.default.circuitBreaker.enabled=false
#禁用hystrix远程调用超时时间
hystrix.command.default.execution.timeout.enabled=false
hystrix.threadpool.default.coreSize=50

Hystrix隔离策略：线程隔离

在Feign调用的时候，会报错：

Caused by: java.util.concurrent.ExecutionException: Observable onError
        at rx.internal.operators.BlockingOperatorToFuture$2.getValue(BlockingOperatorToFuture.java:118) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.BlockingOperatorToFuture$2.get(BlockingOperatorToFuture.java:102) ~[rxjava-1.3.8.jar!/:1.3.8]
        at com.netflix.hystrix.HystrixCommand$4.get(HystrixCommand.java:423) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.HystrixCommand.execute(HystrixCommand.java:344) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        ... 30 more
Caused by: java.lang.IllegalArgumentException
        at java.util.concurrent.ThreadPoolExecutor.setCorePoolSize(ThreadPoolExecutor.java:1535) ~[?:?]
        at com.netflix.hystrix.HystrixThreadPool$HystrixThreadPoolDefault.touchConfig(HystrixThreadPool.java:230) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.HystrixThreadPool$HystrixThreadPoolDefault.getScheduler(HystrixThreadPool.java:205) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand.executeCommandWithSpecifiedIsolation(AbstractCommand.java:710) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand.executeCommandAndObserve(AbstractCommand.java:638) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand.applyHystrixSemantics(AbstractCommand.java:546) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand.access$200(AbstractCommand.java:60) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand$4.call(AbstractCommand.java:419) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at com.netflix.hystrix.AbstractCommand$4.call(AbstractCommand.java:413) ~[hystrix-core-1.5.18.jar!/:1.5.18]
        at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:46) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:35) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:41) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:30) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:41) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:30) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8]
        at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:51) ~[rxjava-1.3.8.jar!/:1.3.8]

重启有时候复现，有时候不复现，估计是和类加载还有初始化顺序有关的问题。

问题定位

查看问题源代码, 对于每个微服务调用，初始化Hytrix线程池，动态读取配置：

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);
}

报错是在threadPool.setCorePoolSize(dynamicCoreSize);，看下为何：

public void setCorePoolSize(int corePoolSize) {
        if (corePoolSize < 0 || maximumPoolSize < corePoolSize)
            throw new IllegalArgumentException();
    //忽略其他代码
}

发现还有maximumPoolSize < corePoolSize的判断，所以，需要先设置MaximumPoolSize,之后设置CorePoolSize，这样可以避免这个问题

相关ISSUES与解决方案

看了下社区，已经有ISSUE了：https://github.com/Netflix/Hystrix/issues/1874 还有对应的PULL REQUEST：https://github.com/Netflix/Hystrix/pull/1877

但是目前，还没有合并，只好自己改了，项目中增加同名同路径替换类,修改：

//jdk9以上的版本，设置coreSize会验证coreSize必须小于maxSize，所以先改变max再设置core
                threadPool.setMaximumPoolSize(dynamicMaximumSize);
                threadPool.setCorePoolSize(dynamicCoreSize);