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https://issues.apache.org/jira/browse/LUCENE-3800?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler updated LUCENE-3800:
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Attachment: LUCENE-3800.patch
Patch for trunk that enforces a "soft-close" (make it unuseable) once a
child-reader (subreader, delegate, parallel reader) is closed.
The implementation works like that:
- A parent reader that delegates to one or more child readers (its currently
BaseCompositeReader, SlowCompositeReaderWrapper, FilterAtomicReader,
ParallelAtomicReader), register itsself on every child/delegate reader. The
registration is done using a weak reference, so there is no circular ref
problems. To be able to use WeakHashMap, this patch explicitely enforces
identity equals/hashcode on IndexReader (which we always assumedin the past for
FieldCache and so on, now its enforced like in MMapIndexInput)
- When a reader closes, it simply iterates over all registered parents and
"marks" them as "unuseable" (they are not really closed).
- When somebody calls any method of a reader of which any child was closed,
ensureOpen() will throw an AlreadyClosedEx with corresponding message.
- You are still able to decRef/close readers which are marked as invalid
(otherwise tests would fail). The child reader closed -> disable parent reader
is simply done for safety.
- To make the ensureOpen() checks not more expensive than before, the extra
boolean was not made volatile, instead happens before and volatile behaviour as
explained in Michael Busch's talks was used to guard the "closedByChild"
boolean.
- The patch does not use readerClosedListener for 2 reasons: (1) RCL has no
weak refs, so we don't produce circular references between parents and childs,
(2) We have to recursively go up the parent chain, which may confuse
conventional readerClosedListeners. Also the parent readers are not closed, so
its not applicable to call the listeners.
> Readers wrapping other readers don't prevent usage if any of their subreaders
> was closed
> ----------------------------------------------------------------------------------------
>
> Key: LUCENE-3800
> URL: https://issues.apache.org/jira/browse/LUCENE-3800
> Project: Lucene - Java
> Issue Type: Bug
> Components: core/index
> Affects Versions: 4.0
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Fix For: 4.0
>
> Attachments: LUCENE-3800.patch
>
>
> On recent trunk test we got this problem:
> org.apache.lucene.index.TestReaderClosed.test
> fails because the inner reader is closed but the wrapped outer ones are still
> open.
> I fixed the issue partially for SlowCompositeReaderWrapper and
> ParallelAtomicReader but it failed again. The cool thing with this test is
> the following:
> The test opens an DirectoryReader and then creates a searcher, closes the
> reader and executes a search. This is not an issue, if the reader is closed
> that the search is running on. This test uses LTC.newSearcher(wrap=true),
> which randomly wraps the passed Reader with SlowComposite or ParallelReader -
> or with both!!! If you then close the original inner reader, the close is not
> detected when excuting search. This can cause SIGSEGV when MMAP is used.
> The problem in (in Slow* and Parallel*) is, that both have their own Fields
> instances thats are kept alive until the reader itsself is closed. If the
> child reader is closed, the wrapping reader does not know and still uses its
> own Fields instance that delegates to the inner readers. On this step no more
> ensureOpen checks are done, causing the failures.
> The first fix done in Slow and Parallel was to call ensureOpen() on the
> subReader, too when requesting fields(). This works fine until you wrap two
> times:
> ParallelAtomicReader(SlowCompositeReaderWrapper(StandardDirectoryReader(segments_1:3:nrt
> _0(4.0):C42)))
> One solution would be to make ensureOpen also check all subreaders, but that
> would do the volatile checks way too often (with n is the total number of
> subreaders and m is the number of hierarchical levels this is n^m) - we
> cannot do this. Currently we only have n*m which is fine.
> The proposal how to solve this (closing subreaders under the hood of parent
> readers is to use the readerClosedListeners. Whenever a composite or slow
> reader wraps another readers, it registers itself as interested in
> readerClosed events. When a subreader is then forcefully closed (e.g by a
> programming error or this crazy test), we automatically close the parents,
> too.
> We should also fix this in 3.x, if we have similar problems there (needs
> investigation).
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