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https://issues.apache.org/jira/browse/SLING-2786?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lukas Eder updated SLING-2786:
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Attachment: ResourceMetadata.java.clone.patch
I agree that a Javadoc disclaimer is the path of least resistance :-)
Issues tend to pile up because of the fact that ResourceMetadata *extends*
HashMap instead of implementing Map and delegating to an internal HashMap. Of
course, removing HashMap from the type hierarchy would introduce a
backwards-incompatibility in the Sling API, so I'm not sure if that's a viable
approach. Anyway, fixing these Map views is off-topic for this issue, which is
about clone(). I'll let you decide how to proceed with the Map views.
I have attached a patch containing a fix for clone(). The failing test cases
for invalid Map view manipulation are also contained in the patch. Feel free to
remove those test cases.
> ResourceMetadata contains stale unmodifiableMap cache after clone()
> -------------------------------------------------------------------
>
> Key: SLING-2786
> URL: https://issues.apache.org/jira/browse/SLING-2786
> Project: Sling
> Issue Type: Bug
> Components: API
> Affects Versions: API 2.3.0
> Reporter: Lukas Eder
> Priority: Minor
> Attachments: ResourceMetadata.java.clone.patch,
> ResourceMetadataTest.java.patch
>
>
> Super types of ResourceMetadata (java.util.HashMap and java.util.AbstractMap)
> correctly implement caching for members such as entrySet, keySet, values,
> etc. Two things should be considered:
> 1. The cache should be marked transient. It is not desireable to serialise /
> deserialise the "unmodifiableMap" cache. Only the isReadOnly flag should be
> serialised
> 2. clone() should be overridden in order to reset the cache on cloned
> instances
> Consider the following code:
> ResourceMetadata map1 = new ResourceMetadata();
> map1.put("key1", "value1");
> map1.lock();
> map1.values(); // Enforce the creation of the cache
> ResourceMetadata map2 = (ResourceMetadata) map1.clone();
> Now, map2 contains an unmodifiable wrapper of map1. While this generally
> behaves correctly, there are two problems:
> a) This is a potential memory leak as clones hold a reference to the original
> map.
> b) If unlock() is ever added, this might lead to a subtle bug when (after the
> above code):
> - map1.unlock() is called
> - map1 is modified
> - map2 will reflect map1's modifications, even if map2 should still be
> locked
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