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From "Xiao-Feng Li" <xiaofeng...@gmail.com>
Subject Re: [jira] Commented: (HARMONY-3883) [classlib]WeakHashMap.keySet().toArray() intermittently throws NoSuchElementException in java.lang.ThreadTest of DRLVM kernel test
Date Thu, 24 May 2007 01:24:50 GMT
Mike, I will commit your patch2, and close this issue, while opening
another JIRA for the java.lang.ThreadGroup.java issue. The goal is to
solve this java.lang.ThreadTest failure finally.

Thanks,
xiaofeng

On 5/24/07, Mikhail Markov (JIRA) <jira@apache.org> wrote:
>
>     [ https://issues.apache.org/jira/browse/HARMONY-3883?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12498283
]
>
> Mikhail Markov commented on HARMONY-3883:
> -----------------------------------------
>
> Xio-feng, i guess you've posted your comment to the wrong JIRA :-).
>
> > [classlib]WeakHashMap.keySet().toArray() intermittently throws NoSuchElementException
in java.lang.ThreadTest of DRLVM kernel test
> > ----------------------------------------------------------------------------------------------------------------------------------
> >
> >                 Key: HARMONY-3883
> >                 URL: https://issues.apache.org/jira/browse/HARMONY-3883
> >             Project: Harmony
> >          Issue Type: Bug
> >          Components: Classlib
> >         Environment: win/linux 32/64
> >            Reporter: Li-Gang Wang
> >         Attachments: H-3883.patch, H-3883_add_alt1.patch, H-3883_add_alt2.patch,
WeakHashmapTest.java
> >
> >
> > I found there is a design bug in WeakHashMap.keySet().toArray() .
> > WeakHashMap.keySet().toArray() inherits AbstractCollection.toArray(). Its implementation
is as follows:
> >       public Object[] toArray() {
> >               int size = size(), index = 0;
> >               Iterator<?> it = iterator();
> >               Object[] array = new Object[size];
> >               while (index < size) {
> >             array[index++] = it.next();
> >         }
> >               return array;
> >       }
> > After assigning 'size()' to 'size', the 'while' loop expects 'size' elements in
the iterator 'it'. But actually GC might happen and clear some weak keys of the WeakHashMap
instance in the meantime. The iterator will skip the cleared weak keys in 'it.hasNext()' called
by 'it.next()', so the actual number of the elements in 'it' is smaller than 'size'. When
'it' runs out its elements, 'it.next()' will throw a NoSuchElementException. Parts of HashIterator
implementation in WeakHashMap is as follows:
> >         public boolean hasNext() {
> >             if (nextEntry != null) {
> >                 return true;
> >             }
> >             while (true) {
> >                 if (nextEntry == null) {
> >                     while (position < elementData.length) {
> >                         if ((nextEntry = elementData[position++]) != null) {
> >                             break;
> >                         }
> >                     }
> >                     if (nextEntry == null) {
> >                         return false;
> >                     }
> >                 }
> >                 // ensure key of next entry is not gc'ed
> >                 nextKey = nextEntry.get();
> >                 if (nextKey != null || nextEntry.isNull) {
> >                     return true;
> >                 }
> >                 nextEntry = nextEntry.next;
> >             }
> >         }
> >         public R next() {
> >             if (expectedModCount == modCount) {
> >                 if (hasNext()) {
> >                     currentEntry = nextEntry;
> >                     nextEntry = currentEntry.next;
> >                     R result = type.get(currentEntry);
> >                     // free the key
> >                     nextKey = null;
> >                     return result;
> >                 }
> >                 throw new NoSuchElementException();
> >             }
> >             throw new ConcurrentModificationException();
> >         }
> > I suspect the intermittent failure in java.lang.ThreadTest may disappear if this
bug is fixed.
>
> --
> This message is automatically generated by JIRA.
> -
> You can reply to this email to add a comment to the issue online.
>
>


-- 
http://xiao-feng.blogspot.com

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