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From "Joe Pallas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5782) BlockListAsLongs should take lists of Replicas rather than concrete classes
Date Wed, 31 Dec 2014 02:26:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5782?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14261810#comment-14261810

Joe Pallas commented on HDFS-5782:

Hmm, the report says Findbugs version 3.0.0 and cites a file that is not touched by the patch.

> BlockListAsLongs should take lists of Replicas rather than concrete classes
> ---------------------------------------------------------------------------
>                 Key: HDFS-5782
>                 URL: https://issues.apache.org/jira/browse/HDFS-5782
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode
>    Affects Versions: 3.0.0
>            Reporter: David Powell
>            Assignee: David Powell
>            Priority: Minor
>         Attachments: HDFS-5782.patch, HDFS-5782.patch
> From HDFS-5194:
> {quote}
> BlockListAsLongs's constructor takes a list of Blocks and a list of ReplicaInfos.  On
the surface, the former is mildly irritating because it is a concrete class, while the latter
is a greater concern due to being a File-based implementation of Replica.
> On deeper inspection, BlockListAsLongs passes members of both to an internal method that
accepts just Blocks, which conditionally casts them *back* to ReplicaInfos (this cast only
happens to the latter, though this isn't immediately obvious to the reader).
> Conveniently, all methods called on these objects are found in the Replica interface,
and all functional (i.e. non-test) consumers of this interface pass in Replica subclasses.
 If this constructor took Lists of Replicas instead, it would be more generally useful and
its implementation would be cleaner as well.
> {quote}
> Fixing this indeed makes the business end of BlockListAsLongs cleaner while requiring
no changes to FsDatasetImpl.  As suggested by the above description, though, the HDFS tests
use BlockListAsLongs differently from the production code -- they pretty much universally
provide a list of actual Blocks.  To handle this:
> - In the case of SimulatedFSDataset, providing a list of Replicas is actually less work.
> - In the case of NNThroughputBenchmark, rewriting to use Replicas is fairly invasive.
 Instead, the patch creates a second constructor in BlockListOfLongs specifically for the
use of NNThrougputBenchmark.  It turns the stomach a little, but is clearer and requires less
code than the alternatives (and isn't without precedent).  

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