[ACCUMULO-4469] ConcurrentModificationException while running MultiTable.xml node in Random Walk

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.7.2
• Fix Version/s: 1.7.3, 1.8.1, 2.0.0
• Component/s: test
• Assignee: Dima Spivak
• Reporter: Dima Spivak
• Created: 23/Sep/16 01:26
• Updated: 18/Oct/16 19:21
• Resolved: 26/Sep/16 02:31

Description

After the resolution of ACCUMULO-4467, I got back to playing with Random Walk and had a failure caused by a ConcurrentModificationException:

23 01:03:04,316 [randomwalk.Framework] ERROR: Error during random walk
java.lang.Exception: Error running node MultiTable.xml
        at org.apache.accumulo.test.randomwalk.Module.visit(Module.java:346)
        at org.apache.accumulo.test.randomwalk.Framework.run(Framework.java:59)
        at org.apache.accumulo.test.randomwalk.Framework.main(Framework.java:119)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.apache.accumulo.start.Main$2.run(Main.java:157)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.ConcurrentModificationException
        at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
        at java.util.ArrayList$Itr.next(ArrayList.java:831)
        at org.apache.accumulo.test.randomwalk.multitable.MultiTableFixture.tearDown(MultiTableFixture.java:64)
        at org.apache.accumulo.test.randomwalk.Module.visit(Module.java:365)
        at org.apache.accumulo.test.randomwalk.Module$1.call(Module.java:283)
        at org.apache.accumulo.test.randomwalk.Module$1.call(Module.java:278)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at org.apache.accumulo.fate.util.LoggingRunnable.run(LoggingRunnable.java:35)
        ... 1 more

This section of code seems to be at fault. In particular, it looks like we're getting the table list, but then instead of doing a deep copy to a new ArrayList<String> from which we choose tables to delete, we're looping through and deleting tables while referring to the changing list, which has the effect of modifying it and making Java unhappy. Am I missing something more complex or can I fix this one myself by just doing the aforementioned deep copy of the table list? Or is a better way to use the TableOperations.list() method and iterate through the SortedSet<String> it provides?