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https://issues.apache.org/jira/browse/LUCENE-818?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12477713
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Michael McCandless commented on LUCENE-818:
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>> On the thread safety issue: are you saying if one thread closes the
>> reader while another thread is using it, there is uncertainty excactly
>> when the 2nd thread will hit the AlreadyClosedException (because of
>> how the JVM schedules the threads)?
>
> Yes, but it's not just thread scheduling, it's also lack of memory
> barriers. The 2nd thread may *never* see the close(), depending on
> the exact architecture of machine and the JVM.
Yikes. Is this the Java memory model issue? Ie, there is no hard
guarantee on when a "write" from one thread will be visible to other
threads, unless you use "volatile"?
>> I think this kind of thread behavior is normal/expected?
>
> For a class that isn't thread safe, yes. IndexReader is advertised
> as being thread safe though. If we guarantee an exception accessing
> a closed reader, then that should work 100% of the time. I don't
> think we should make that guarantee.
OK I think we shouldn't "guarantee" it. I think listing as "@throws
AlreadyClosedException if this IndexReader is closed" is OK?
> We can still throw meaningful errors in more cases and make it
> easier for the user to debug that, but it should not be deemed an
> error if we don't throw an exception. Users should never rely on
> getting this exception for flow-control purposes anyway.
Agreed.
>> OK how about we do not call ensureOpen() in these IndexReader methods?:
>> numDoc()
>> maxDoc()
>> isDeleted()
>
> +1
>
> hasDeletions() too?
OK I will change to not call ensureOpen() for hasDeletions too. I
will roll a new patch with this.
>> > what about setting more things to null when a reader is closed?
>> Well ... I would prefer not to increase the frequency of getting "undefined"
>> NPEs out of the reader
>
> Yes, but not all bugs will be user bugs. Some will be internal
> Lucene stuff that bypass public methods. It's still better that
> these fail quicker too. Anyway, that can be handled on a
> case-by-case basis later.
OK, I agree. Better to throw a "fail-fast" NPE than do something
strange later.
> IndexWriter should detect when it's used after being closed
> -----------------------------------------------------------
>
> Key: LUCENE-818
> URL: https://issues.apache.org/jira/browse/LUCENE-818
> Project: Lucene - Java
> Issue Type: Bug
> Components: Index
> Affects Versions: 2.1
> Reporter: Michael McCandless
> Assigned To: Michael McCandless
> Priority: Minor
> Attachments: LUCENE-818.patch, LUCENE-818.take2.patch
>
>
> Spinoff from this thread on java-user:
> http://www.gossamer-threads.com/lists/lucene/java-user/45986
> If you call addDocument on IndexWriter after it's closed you'll hit a
> hard-to-explain NullPointerException (because the RAMDirectory was
> closed). Before 2.1, apparently you won't hit any exception and the
> IndexWrite will keep running but will have released it's write lock (I
> think).
> I plan to fix IndexWriter methods to throw an IllegalStateException if
> it has been closed.
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