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From "Uwe Schindler (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (LUCENE-3800) Readers wrapping other readers don't prevent usage if any of their subreaders was closed
Date Sun, 19 Feb 2012 17:56:38 GMT
Readers wrapping other readers don't prevent usage if any of their subreaders was closed
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                 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


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
rewquesting 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 instances 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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