BUG背景
JDK: 11.0.4 Spring Cloud Finchley.SR3
相关配置：
1#开启hystrix 2feign.hystrix.enabled=true 3#关闭断路器 4hystrix.command.default.circuitBreaker.enabled=false 5#禁用hystrix远程调用超时时间 6hystrix.command.default.execution.timeout.enabled=false 7hystrix.threadpool.default.coreSize=50
Hystrix隔离策略：线程隔离
在Feign调用的时候，会报错：
1Caused by: java.util.concurrent.ExecutionException: Observable onError 2 at rx.internal.operators.BlockingOperatorToFuture$2.getValue(BlockingOperatorToFuture.java:118) ~[rxjava-1.3.8.jar!/:1.3.8] 3 at rx.internal.operators.BlockingOperatorToFuture$2.get(BlockingOperatorToFuture.java:102) ~[rxjava-1.3.8.jar!/:1.3.8] 4 at com.netflix.hystrix.HystrixCommand$4.get(HystrixCommand.java:423) ~[hystrix-core-1.5.18.jar!/:1.5.18] 5 at com.netflix.hystrix.HystrixCommand.execute(HystrixCommand.java:344) ~[hystrix-core-1.5.18.jar!/:1.5.18] 6 ... 30 more 7Caused by: java.lang.IllegalArgumentException 8 at java.util.concurrent.ThreadPoolExecutor.setCorePoolSize(ThreadPoolExecutor.java:1535) ~[?:?] 9 at com.netflix.hystrix.HystrixThreadPool$HystrixThreadPoolDefault.touchConfig(HystrixThreadPool.java:230) ~[hystrix-core-1.5.18.jar!/:1.5.18] 10 at com.netflix.hystrix.HystrixThreadPool$HystrixThreadPoolDefault.getScheduler(HystrixThreadPool.java:205) ~[hystrix-core-1.5.18.jar!/:1.5.18] 11 at com.netflix.hystrix.AbstractCommand.executeCommandWithSpecifiedIsolation(AbstractCommand.java:710) ~[hystrix-core-1.5.18.jar!/:1.5.18] 12 at com.netflix.hystrix.AbstractCommand.executeCommandAndObserve(AbstractCommand.java:638) ~[hystrix-core-1.5.18.jar!/:1.5.18] 13 at com.netflix.hystrix.AbstractCommand.applyHystrixSemantics(AbstractCommand.java:546) ~[hystrix-core-1.5.18.jar!/:1.5.18] 14 at com.netflix.hystrix.AbstractCommand.access$200(AbstractCommand.java:60) ~[hystrix-core-1.5.18.jar!/:1.5.18] 15 at com.netflix.hystrix.AbstractCommand$4.call(AbstractCommand.java:419) ~[hystrix-core-1.5.18.jar!/:1.5.18] 16 at com.netflix.hystrix.AbstractCommand$4.call(AbstractCommand.java:413) ~[hystrix-core-1.5.18.jar!/:1.5.18] 17 at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:46) ~[rxjava-1.3.8.jar!/:1.3.8] 18 at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:35) ~[rxjava-1.3.8.jar!/:1.3.8] 19 at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8] 20 at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48) ~[rxjava-1.3.8.jar!/:1.3.8] 21 at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33) ~[rxjava-1.3.8.jar!/:1.3.8] 22 at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8] 23 at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:41) ~[rxjava-1.3.8.jar!/:1.3.8] 24 at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:30) ~[rxjava-1.3.8.jar!/:1.3.8] 25 at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) ~[rxjava-1.3.8.jar!/:1.3.8] 26 at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) ~[rxjava-1.3.8.jar!/:1.3.8] 27 at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8] 28 at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:41) ~[rxjava-1.3.8.jar!/:1.3.8] 29 at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:30) ~[rxjava-1.3.8.jar!/:1.3.8] 30 at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar!/:1.3.8] 31 at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:51) ~[rxjava-1.3.8.jar!/:1.3.8] 32
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：
1private void touchConfig() { 2 final int dynamicCoreSize = properties.coreSize().get(); 3 final int configuredMaximumSize = properties.maximumSize().get(); 4 int dynamicMaximumSize = properties.actualMaximumSize(); 5 final boolean allowSizesToDiverge = properties.getAllowMaximumSizeToDivergeFromCoreSize().get(); 6 boolean maxTooLow = false; 7 8 if (allowSizesToDiverge && configuredMaximumSize < dynamicCoreSize) { 9 //if user sets maximum < core (or defaults get us there), we need to maintain invariant of core <= maximum 10 dynamicMaximumSize = dynamicCoreSize; 11 maxTooLow = true; 12 } 13 14 // In JDK 6, setCorePoolSize and setMaximumPoolSize will execute a lock operation. Avoid them if the pool size is not changed. 15 if (threadPool.getCorePoolSize() != dynamicCoreSize || (allowSizesToDiverge && threadPool.getMaximumPoolSize() != dynamicMaximumSize)) { 16 if (maxTooLow) { 17 logger.error("Hystrix ThreadPool configuration for : " + metrics.getThreadPoolKey().name() + " is trying to set coreSize = " + 18 dynamicCoreSize + " and maximumSize = " + configuredMaximumSize + ". Maximum size will be set to " + 19 dynamicMaximumSize + ", the coreSize value, since it must be equal to or greater than the coreSize value"); 20 } 21 threadPool.setCorePoolSize(dynamicCoreSize); 22 threadPool.setMaximumPoolSize(dynamicMaximumSize); 23 } 24 25 threadPool.setKeepAliveTime(properties.keepAliveTimeMinutes().get(), TimeUnit.MINUTES); 26}
报错是在 threadPool.setCorePoolSize(dynamicCoreSize);，看下为何：
1public void setCorePoolSize(int corePoolSize) { 2 if (corePoolSize < 0 || maximumPoolSize < corePoolSize) 3 throw new IllegalArgumentException(); 4 //忽略其他代码 5}
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：
1//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 2 threadPool.setMaximumPoolSize(dynamicMaximumSize); 3 threadPool.setCorePoolSize(dynamicCoreSize);