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From "Lei (Eddy) Xu (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-7496) Fix FsVolume removal race conditions on the DataNode
Date Wed, 31 Dec 2014 03:05:13 GMT

     [ https://issues.apache.org/jira/browse/HDFS-7496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Lei (Eddy) Xu updated HDFS-7496:
    Attachment: HDFS-7496.001.patch

Thanks for the reviews, [~cmccabe]. They are very helpful. I have made changes accordingly,
detailed as following:

bq. * Rather than having a boolean hasReference, let's have an actual pointer to the FsVolumeSpi
bq. * We should release the reference count in close(), not in the finally block
bq. * We don't need this code any more:


bq. This change seems unrelated to this JIRA... 

Yes, this is not related. I removed it from this patch. I should follow another JIRA to use
{{File#canonicalPath}} to compare the volumes. But it should not throw {{IOE}} for {{File#getCanonicalPath()}},
as you mentioned above.

bq. How about using Preconditions.checkNonNull here... might look nicer

It is for simplifying the test code, i.e., it does not need to construct a {{Datanode}} object
for {{FsVolumeImpl}} tests.

bq. What I was envisioning was having getNextVolume increment the reference count when it
retrieved the volume, 

{{getNextVolume}} is not the only place to pass an _active_ volume. I have made the change
that if BlockReceiver's constructor successes, it must hold a reference count from {{FsDatasetImpl#createRbw/createTemporary/append/recoverRbw/recoverAppend}}.
Also I added a {{FsVolumeReference}} helper class to let the caller use {{try-with-resources}}
on the reference count.

> Fix FsVolume removal race conditions on the DataNode 
> -----------------------------------------------------
>                 Key: HDFS-7496
>                 URL: https://issues.apache.org/jira/browse/HDFS-7496
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Colin Patrick McCabe
>            Assignee: Lei (Eddy) Xu
>         Attachments: HDFS-7496.000.patch, HDFS-7496.001.patch
> We discussed a few FsVolume removal race conditions on the DataNode in HDFS-7489.  We
should figure out a way to make removing an FsVolume safe.

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