[
http://issues.apache.org/jira/browse/EXLBR-26?page=comments#action_12316034 ]
Kazimierz Pogoda commented on EXLBR-26:
---------------------------------------
OK, you are right :)
I misunderstood the api. So i've changed the test as you did (resource with
unique file for every thread - new FileResource("/tmp/" + i), and now i've got
this stacktrace:
Exception in thread "Thread-0" java.util.NoSuchElementException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:790)
at java.util.HashMap$ValueIterator.next(HashMap.java:817)
at java.util.AbstractCollection.toArray(AbstractCollection.java:176)
at
org.apache.avalon.excalibur.monitor.impl.AbstractMonitor.getResources(AbstractMonitor.java:152)
at
org.apache.avalon.excalibur.monitor.impl.AbstractMonitor.scanAllResources(AbstractMonitor.java:161)
at
org.apache.avalon.excalibur.monitor.impl.ActiveMonitor.run(ActiveMonitor.java:136)
at java.lang.Thread.run(Thread.java:595)
or:
Exception in thread "Thread-0" java.lang.NullPointerException
at
org.apache.avalon.excalibur.monitor.impl.AbstractMonitor.scanAllResources(AbstractMonitor.java:164)
at
org.apache.avalon.excalibur.monitor.impl.ActiveMonitor.run(ActiveMonitor.java:136)
at java.lang.Thread.run(Thread.java:595)
My enviroment:
linux 2.6.x
java version "1.5.0_03"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_03-b07)
Java HotSpot(TM) Client VM (build 1.5.0_03-b07, mixed mode, sharing)
excalibur-monitor-1.0.2.jar
IMHO the bug is caused by the following thing:
protected Resource[] getResources()
{
final Collection collection = m_resources.values();
return (Resource[])collection.toArray( new Resource[ collection.size() ] );
}
If Thread1 calls collection.size() and allocates new array with this size and
then goes inside toArray() method, then VM can switch to Thread2 which can
change number of elements in m_resources map during execution of toArray(). So
we can expect NoSuchElementException and ConcurrentModificationException (from
iterator), and also NullPointerException if last elements in array returned by
toArray() method are null.
There is another thing i want to notice:
public final void removeResource( final String key )
Can throw NullPointerException if there is no resource with given key. It
should be documented, and maybe changed to IllegalArgumentException or event
checked exception.
> org.apache.avalon.excalibur.monitor.impl.ActiveMonitor is not thread safe
> -------------------------------------------------------------------------
>
> Key: EXLBR-26
> URL: http://issues.apache.org/jira/browse/EXLBR-26
> Project: Excalibur Components
> Type: Bug
> Components: Monitor
> Versions: 1.0.2
> Environment: Linux 2.6.11 + jdk5.0
> Reporter: Kazimierz Pogoda
>
> getResources() method of the AbstractMonitor should be probably synchronized
> on m_resources like the other methods in this class.
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