Good catch! Thanks, Ligang. The intermittent failure of
java.lang.ThreadTest has been annoying for a long time.
Thanks,
xiaofeng
On 5/17/07, Li-Gang Wang (JIRA) <[EMAIL PROTECTED]> wrote:
[
https://issues.apache.org/jira/browse/HARMONY-3883?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Li-Gang Wang updated HARMONY-3883:
----------------------------------
Attachment: WeakHashmapTest.java
I modified the WeakHashmapTest.java in DRLVM smoke test so that it can easily
make this problem appear. Just replace the original one in
$drlvm/vm/tests/smoke/stress/WeakHashmapTest.java with the attachment and try
to run it individually.
> [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: 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
