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https://issues.apache.org/jira/browse/LUCENE-4711?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13560805#comment-13560805
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Adrien Grand commented on LUCENE-4711:
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bq. the JVM implementation can decide to allocate small arrays outside the heap
space .. so what does it mean? Is it not safe to save a reference to a vararg
parameter?
My understanding is that the JVM can decide to allocate small objects on the
stack if the object is small (for some definition of small) enough and if it is
safe to do so (the object doesn't escape the scope of the compiled method). So
it is perfectly safe to save any object reference.
> IBM J9 1.7.0 JIT bug in CategoryPath
> ------------------------------------
>
> Key: LUCENE-4711
> URL: https://issues.apache.org/jira/browse/LUCENE-4711
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/facet
> Reporter: Shai Erera
> Assignee: Shai Erera
> Fix For: 4.2, 5.0
>
> Attachments: JavaVarargsBug.java
>
>
> When running facet tests with IBM J9 1.7.0, most of the tests fail with
> bizarre exceptions from CategoryPath (AIIOBE mostly). I tried to add few
> asserts to CategoryPath, but they didn't help to reveal the bug.
> Today I ran a single test {{TestAssociationExample}} (randomly picked) w/
> -Dtests.iters=1000 and it failed too on the same error. If run w/ -Xint, it
> doesn't fail.
> In the end, Gilad and I discovered that when {{CategoryPath(String...
> components)}} constructor is used, which inside does {{this.components =
> components}}, the bug is triggered. At some point, probably after JIT kicks
> in, the array's length is 0'ed !!!
> We've added the following workaround to CategoryPath:
> {code}
> // TODO: revisit when IBM releases Java 7 newer than SR3 (with a fix)
> // to validate, run e.g. TestAssociationExample with -Dtests.iters=1000
> private static final boolean IS_J9_JAVA7 = Constants.JRE_IS_MINIMUM_JAVA7 &&
> Constants.JVM_VENDOR.contains("IBM");
> ...
> public CategoryPath(final String... components) {
> assert components.length > 0 : "use CategoryPath.EMPTY to create an empty
> path";
> if (IS_J9_JAVA7) {
> // On IBM J9 Java 1.7.0, if we do 'this.components = components', then
> // at some point its length becomes 0 ... quite unexpectedly. If JIT is
> // disabled, it doesn't happen. This bypasses the bug by copying the
> // array (note, Arrays.copyOf did not help either!).
> this.components = new String[components.length];
> System.arraycopy(components, 0, this.components, 0, components.length);
> } else {
> this.components = components;
> }
> length = components.length;
> }
> {code}
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