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https://issues.apache.org/jira/browse/CASSANDRA-414?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753970#action_12753970
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Jonathan Ellis commented on CASSANDRA-414:
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Yeah, it's a little subtle. The article I linked is a good explanation, the
javadoc alone isn't sufficient or at least wasn't for me.
A Reference of any type has a get() method that returns the actual referent.
Here that would be the SSTR. But ReferenceQueue holds the Reference wrapper,
not the actual SSTRs. (When you pass a RQ to the Reference constructor, the
Reference will be enqueued on that RQ when its referent is GC'd. The referent
itself already GC'd or in the process of being GC'd so it can't be put on the
RQ or you would get back to the Bad Old Days of finalizer resurrection bugs.)
Now, if the referent is no longer live, get() will return null. Since the
point of the RQ design is to do cleanup after the object is dead, we subclass
PhantomReference and store a reference to the path, so we don't actually need
the SSTR to do the delete. (In fact for PR in particular get() _always_
returns null but that is not really essential to understanding what is going on
here.)
> remove sstableLock
> ------------------
>
> Key: CASSANDRA-414
> URL: https://issues.apache.org/jira/browse/CASSANDRA-414
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Jonathan Ellis
> Assignee: Jonathan Ellis
> Fix For: 0.5
>
> Attachments:
> 0001-CASSANDRA-414-combine-addToList-and-storeLocation-ren.txt,
> 0001-CASSANDRA-414-combine-addToList-and-storeLocation-ren.txt,
> 0001-CASSANDRA-414-combine-addToList-and-storeLocation-ren.txt,
> 0002-convert-ssTables_-to-a-Set-since-the-filename-is-enca.txt,
> 0002-remove-sstableLock.-re-order-a-few-ops-so-that-we-can.txt,
> 0002-remove-sstableLock.-re-order-a-few-ops-so-that-we-can.txt,
> 0003-Replace-sstableLock-with-SSTableTracker-which-perform.txt
>
>
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