Minor Description
This was reported by Shai. The runner failed with an exception:
[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
The problem is that this is impossible because the code around JUnit4.java:809 looks like this:
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(); ... } } });
and the contract on Guava's EventBus states that:
* <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
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.