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https://issues.apache.org/jira/browse/HDFS-7758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14523713#comment-14523713
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Colin Patrick McCabe edited comment on HDFS-7758 at 5/1/15 7:05 PM:
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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.
was (Author: cmccabe):
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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