[GitHub] [cayenne] shunfan-shao opened a new pull request #472: Fix concurrent map flakiness

[GitBox <gi...@apache.org>]

shunfan-shao opened a new pull request #472:
URL: https://github.com/apache/cayenne/pull/472


   # Description
   Test `org.apache.cayenne.util.WeakValueMapTest.testConcurrentModification` will fail under [NonDex](https://github.com/TestingResearchIllinois/NonDex) which detects flakiness under non-deterministic environment. 
   
   To reproduce:
   ```
   mvn edu.illinois:nondex-maven-plugin:1.1.2:nondex \
       -pl cayenne-server \
       -Dtest=org.apache.cayenne.util.WeakValueMapTest#testConcurrentModification
   ```
   
   # Issue
   The test code follows the logic below:
   ```java
   Map<String, Integer> map = new WeakValueMap<>(3);
   for(Map.Entry<String, Integer> entry : map.entrySet()) {
       if("key_2".equals(entry.getKey())) 
           map.remove("key_2");
   }
   ```
   
   While [WeakValueMap uses HashMap internally](https://github.com/apache/cayenne/blob/master/cayenne-server/src/main/java/org/apache/cayenne/util/ReferenceMap.java#L76), it is not guaranteed for `map.entrySet` to iterate over the entries under some orders.
   
   The code is expected to thrown `ConcurrentModificationException` during execution. Under some edge cases, eg: `key_2` is traversed and removed last, the test will fail to throw and cause an issue. 


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