[jira] [Created] (FLINK-24569) Flaky Test in NFATest

["Hang Xie (Jira)" <ji...@apache.org>]

Hang Xie created FLINK-24569:
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             Summary: Flaky Test in NFATest
                 Key: FLINK-24569
                 URL: https://issues.apache.org/jira/browse/FLINK-24569
             Project: Flink
          Issue Type: Improvement
            Reporter: Hang Xie


I noticed there is a potential flaky test in org.apache.flink.cep.nfa.NFATest file.

 

For example, in the "testNFASerialization" test, ** we try to compare the deserialization result of nfaState and its copy. However, I noticed that to compare whether two nfaState objects are equal, we need to check whether their partialMatches and completedMatches are equal. 

 

"partialMatches" and "completedMatches" are two priority queues, and when we need to compare whether these two priority queues are the same, we need to first cast both priority queues to arrays. 

 

I noticed we write a customized COMPUTATION_STATE_COMPARATOR for both priority queues. However, this comparator only compares the event's timestamp and id. If, in some cases, we have two events who share the same timestamp and id, but have different version, or we have two events without timestamp and id, their order in the priority queues will than become indeterministic. 

 

Here is what the official documentation says about the order in priority queue (https://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html):
{quote}This class and its iterator implement all of the _optional_ methods of the [Collection|https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html] and [Iterator|https://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html] interfaces. The Iterator provided in method [iterator()|https://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html#iterator()] is _not_ guaranteed to traverse the elements of the priority queue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()).
{quote}
 

Thus, the assertion (flink-libraries/flink-cep/src/test/java/org/apache/flink/cep/nfa/NFATest.java:372) here will fail in some platforms or specific machines that adopt a different iteration order. 



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