Summary:
The problem
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ComparatorOptions is AutoCloseable.
AbstractComparator does not hold a reference to its ComparatorOptions, but the native C++ ComparatorJniCallback holds a reference to the ComparatorOptions’ native C++ options structure. This gets deleted when the ComparatorOptions is closed, either explicitly, or as part of try-with-resources.
Later, the deleted C++ options structure gets used by the callback and the comparator options are effectively random.
The original bug report https://github.com/facebook/rocksdb/issues/8715 was caused by a GC-initiated finalization closing the still-in-use ComparatorOptions. As of 7.0, finalization of RocksDB objects no longer closes them, which worked round the reported bug, but still left ComparatorOptions with a potentially broken lifetime.
In any case, we encourage API clients to use the try-with-resources model, and so we need it to work. And if they don't use it, they leak resources.
The solution
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The solution implemented here is to make a copy of the native C++ options object into the ComparatorJniCallback, rather than a reference. Then the deletion of the native object held by ComparatorOptions is *correctly* deleted when its scope is closed in try/finally.
Testing
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We added a regression unit test based on the original test for the reported ticket.
This checkin closes https://github.com/facebook/rocksdb/issues/8715
We expect that there are more instances of "lifecycle" bugs in the Java API. They are a major source of support time/cost, and we note that they could be addressed as a whole using the model proposed/prototyped in https://github.com/facebook/rocksdb/pull/10736
Pull Request resolved: https://github.com/facebook/rocksdb/pull/11176
Reviewed By: cbi42
Differential Revision: D43160885
Pulled By: pdillinger
fbshipit-source-id: 60b54215a02ad9abb17363319650328c00a9ad62
Alan Paxton
d47126875b