[jira] [Commented] (HDFS-7758) Retire FsDatasetSpi#getVolumes() and use FsDatasetSpi#getVolumeRefs() instead

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-7758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14523713#comment-14523713 ] 

Colin Patrick McCabe commented on HDFS-7758:
--------------------------------------------

Thanks, [~eddyxu].  Looks good overall.

Given that we have a class named {{FsVolumeReference}}, we should consistently refer to "Volume references" rather than "referred volumes" So let's change {{ReferredFsVolumes}} -> {{FsVolumeReferences}}.

It would be nice to avoid all the typecasts.  I think we can, if we change FsVolumeReference -> FsVolumeReference<? extends FsVolumeSpi> and FsVolumeReferences -> FsVolumeReferences<? extends FsVolumeSpi>.  But let's do that in a follow-on change-- this change is big enough already.

{{FsDatasetImpl#volumes}} is still package-private rather than truly private.  Can you make it private?  Otherwise other code in this package can reach in and use this field directly.  I also think we should just get rid of {{FsDatasetImpl#getVolumes}}... objects don't need to use accessors for private internal fields.  As long as that function exists there will be a temptation to make it more accessible, like has happened with many other accessors in the past.

> Retire FsDatasetSpi#getVolumes() and use FsDatasetSpi#getVolumeRefs() instead
> -----------------------------------------------------------------------------
>
>                 Key: HDFS-7758
>                 URL: https://issues.apache.org/jira/browse/HDFS-7758
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.6.0
>            Reporter: Lei (Eddy) Xu
>            Assignee: Lei (Eddy) Xu
>         Attachments: HDFS-7758.000.patch, HDFS-7758.001.patch, HDFS-7758.002.patch, HDFS-7758.003.patch, HDFS-7758.004.patch, HDFS-7758.005.patch, HDFS-7758.006.patch
>
>
> HDFS-7496 introduced reference-counting  the volume instances being used to prevent race condition when hot swapping a volume.
> However, {{FsDatasetSpi#getVolumes()}} can still leak the volume instance without increasing its reference count. In this JIRA, we retire the {{FsDatasetSpi#getVolumes()}} and propose {{FsDatasetSpi#getVolumeRefs()}} and etc. method to access {{FsVolume}}. Thus it makes sure that the consumer of {{FsVolume}} always has correct reference count.



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