drools规则中的NPE导致CYCLIC_DEPENDENCY和OOM

Question

我们已经用Guvnor UI建立了一个基本的Drools框架。规则是由半技术人员编写的，并且有错误的范围(无论是谁编写的，范围总是存在的：)

昨天，有人写了一条规则，开始抛出NullPoiterException，但Drool似乎将这个异常包装到CYCLIC_DEPENDENCY_ERROR中，并显示相同的异常。

此外，我们在这个问题之后立即(3-4分钟)结束了OOM java.lang.OutOfMemoryError: Java heap space。

Stacktrace获取详细信息：

Feb 2013 08:06:55,447 [ERROR]  (SWF Activity  DroolsActivityTaskList-2.2 229) com.amazon.mobius.csi.workers.droolsengine.DroolsEngineActivitiesImpl:runRules:220 [CYCLIC_DEPENDENCY_ERROR]: Error
 while executing Rules, Please validate all rules against any cyclic dependency
Exception executing consequence for rule "final NON EC" in com.amazon.mobius.csi.workers.droolsengine: java.lang.NullPointerException
        at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
        at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1101)
        at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:1029)
        at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1251)
        at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:708)
        at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:672)
        at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:218)
        at org.drools.impl.StatelessKnowledgeSessionImpl.execute(StatelessKnowledgeSessionImpl.java:295)
        at com.amazon.mobius.csi.workers.droolsengine.DroolsEngineActivitiesImpl.runRules(DroolsEngineActivitiesImpl.java:216)
        at com.amazon.mobius.csi.workers.droolsengine.DroolsEngineActivitiesImpl.executeRules(DroolsEngineActivitiesImpl.java:145)
        at sun.reflect.GeneratedMethodAccessor173.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.amazonaws.services.simpleworkflow.flow.pojo.POJOActivityImplementation.execute(POJOActivityImplementation.java:63)
        at com.amazonaws.services.simpleworkflow.flow.generic.ActivityImplementationBase.execute(ActivityImplementationBase.java:46)
        at com.amazonaws.services.simpleworkflow.flow.worker.SynchronousActivityTaskPoller.execute(SynchronousActivityTaskPoller.java:214)
        at com.amazonaws.services.simpleworkflow.flow.worker.ActivityTaskPoller$2.run(ActivityTaskPoller.java:95)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
        at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
        at com.amazon.mobius.csi.workers.droolsengine.Rule_final_NON_EC.defaultConsequence(Unknown Source)
        at com.amazon.mobius.csi.workers.droolsengine.Rule_final_NON_ECDefaultConsequenceInvoker.evaluate(Unknown Source)
        at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:1091)
        ... 18 more

为什么Drools将其视为CYCLIC_DEPENDENCY并导致OOM？我们可以有其他的问题吗？任何帮助都将不胜感激。

谢谢,

Answer 1

我相信这是规则之间的循环依赖。一条规则的RHS会导致另一条规则被激活，而另一条规则的RHS又会导致第一条规则被激活。因此，存在规则激活的无限循环。

在看不到规则本身的情况下，我建议设置一个议程事件侦听器来记录正在触发的规则。这样，您应该能够看到以这种方式激活的是哪两个规则。下面是这样一个日志监听器的例子：

https://github.com/gratiartis/scattercode-drools-scenarios/blob/master/src/main/java/uk/co/scattercode/drools/util/TrackingAgendaEventListener.java