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From "Dawid Weiss (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4987) Test framework may fail internally under J9 (some serious JVM exclusive-section issue).
Date Mon, 01 Jul 2013 21:19:22 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4987?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13697194#comment-13697194
] 

Dawid Weiss commented on LUCENE-4987:
-------------------------------------

Mhmm... took them a while, don't you think? I mean:
{quote}
I think I found the reason. J9 seems to be optimizing away the following code: [...]
{quote}
took me an hour or so to pinpoint this, even without access to the JIT's source code :)
                
> Test framework may fail internally under J9 (some serious JVM exclusive-section issue).
> ---------------------------------------------------------------------------------------
>
>                 Key: LUCENE-4987
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4987
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Dawid Weiss
>            Assignee: Dawid Weiss
>            Priority: Minor
>             Fix For: 5.0, 4.4
>
>         Attachments: j9.zip
>
>
> This was reported by Shai. The runner failed with an exception:
> {code}
> [junit4:junit4] Caused by: java.util.NoSuchElementException
> [junit4:junit4]         at java.util.ArrayDeque.removeFirst(ArrayDeque.java:289)
> [junit4:junit4]         at java.util.ArrayDeque.pop(ArrayDeque.java:518)
> [junit4:junit4]         at com.carrotsearch.ant.tasks.junit4.JUnit4$1.onSlaveIdle(JUnit4.java:809)
> [junit4:junit4]         ... 17 more
> {code}
> The problem is that this is impossible because the code around JUnit4.java:809 looks
like this:
> {code}
>      final Deque<String> stealingQueue = new ArrayDeque<String>(...);
>      aggregatedBus.register(new Object() {
>         @Subscribe
>         public void onSlaveIdle(SlaveIdle slave) {
>           if (stealingQueue.isEmpty()) {
>             ...
>           } else {
>             String suiteName = stealingQueue.pop();
>             ...
>           }
>         }
>       });
> {code}
> and the contract on Guava's EventBus states that:
> {code}
>  * <p>The EventBus guarantees that it will not call a handler method from
>  * multiple threads simultaneously, unless the method explicitly allows it by
>  * bearing the {@link AllowConcurrentEvents} annotation.  If this annotation is
>  * not present, handler methods need not worry about being reentrant, unless
>  * also called from outside the EventBus
> {code}
> I wrote a simple snippet of code that does it in a loop and indeed, two threads can appear
in the critical section at once. This is not reproducible on Hotspot and only appears to be
the problem on J9/1.7/Windows (J9 1.6 works fine).
> I'll provide a workaround in the runner (an explicit monitor seems to be working) but
this is some serious J9 issue.

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