Corruption of Rete when removing complex NotNodes ------------------------------------------------- Key: JBRULES-2465 URL: https://jira.jboss.org/jira/browse/JBRULES-2465 Project: Drools Issue Type: Bug Security Level: Public (Everyone can see) Components: drools-core Affects Versions: 5.0.1.FINAL Reporter: Andreas Kohn Assignee: Mark Proctor Attachments: drools-core-betanode-remove.diff while working further on our drools integration we came across an odd exception when removing a particular rule: java.lang.IllegalArgumentException: Cannot remove a sink, when the list of sinks is null at org.drools.reteoo.ObjectSource.removeObjectSink(ObjectSource.java:159) at org.drools.reteoo.RightInputAdapterNode.doRemove(RightInputAdapterNode.java:217) at org.drools.common.BaseNode.remove(BaseNode.java:95) at org.drools.reteoo.BetaNode.doRemove(BetaNode.java:275) at org.drools.common.BaseNode.remove(BaseNode.java:95) at org.drools.reteoo.BetaNode.doRemove(BetaNode.java:280) at org.drools.common.BaseNode.remove(BaseNode.java:95) at org.drools.reteoo.RuleTerminalNode.doRemove(RuleTerminalNode.java:387) at org.drools.common.BaseNode.remove(BaseNode.java:95) at org.drools.reteoo.ReteooBuilder.removeRule(ReteooBuilder.java:237) at org.drools.reteoo.ReteooRuleBase.removeRule(ReteooRuleBase.java:371) at org.drools.common.AbstractRuleBase.removeRule(AbstractRuleBase.java:746) While stepping through the code it looked like the network was corrupt (there was indeed no sinks on the ObjectSource, but the node calling removeObjectSink was still linked to it and claiming it as source). The rule itself contains multiple NotNodes, checking a condition that looks like this: not(not(Foo.v = X) and not(Foo.v = Y)) I could track this down to some sort of "loop" in the rete that triggers this when the outer not node is removed. When removing BetaNode#doRemove() first walks along 'rightInput': this.rightInput.remove( context, builder, this, workingMemories ); and eventually _in that call_ it also hits a node that is the direct 'leftInput' of the original beta node. The removal marks that node as visited in the removal context, and when the 'rightInput.remove' returns to the beta node it does not visit the leftInput due to this condition in BetaNode#doRemove(): if ( !context.alreadyVisited( this.leftInput ) ) { this.leftInput.remove( context, builder, this, workingMemories ); } In other words: before the remove the BetaNode had another node that was both referenced directly as 'leftInput', as well as an input to the 'rightInput'. The first removal of the rule "worked", and no exceptions happened. But: any further attempt to re-add the same rule and remove it again lead to the exception above. I was able to fix it with the attached patch, reproduced here: + boolean needRemoveFromLeft = !context.alreadyVisited( this.leftInput ); this.rightInput.remove( context, builder, this, workingMemories ); - if ( !context.alreadyVisited( this.leftInput ) ) { + if ( needRemoveFromLeft ) { this.leftInput.remove( context, builder, this, workingMemories ); } With this patch applied I could add/delete/add the particular rule repeatedly without problems. The attached patch also adds an assert in ObjectSource#removeObjectSink(): when removing a sink from an object source with only one sink the sink was unconditionally replaced with an empty sink, although the argument ObjectSink could be a different sink than the one in the ObjectSource. For CompositeObjectSinkAdapters this case is checked, but not for single sinks. I originally suspected that place to be responsible for the problem I observed but the assertion never fired in my tests. (taken from rules-dev mail "Bug in BetaNode#doRemove()?" -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: https://jira.jboss.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira