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https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638593#action_12638593
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Doug Cutting commented on HADOOP-4044:
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Owen> I would probably use a thread local variable to measure the depth of the
traversal. It isn't great, but it would be encapsulated in LinkResult.
I see. Yuck. It wouldn't in fact be entirely encapsulated, since it would
assume that all the resolution of a path happens in the same thread. Thus we'd
want to mark each of the FileSystem methods that uses a LinkResult final, add
some comments noting that the LinkResult API has this restriction, etc. (It'd
be odd to ever try to run these in different threads, but folks have tried
odder things!) In general, thread locals seem like a poor design choice for
this. They're best for things like caches, to avoid thread contention, rather
than for storing program state, no?
We could instead perhaps add something like a LinkResolution object that keeps
a counter internally that is incremented as the link is resolved. The SPI
would pass this around rather than a Path? Is that better than Dhruba's patch?
> Create symbolic links in HDFS
> -----------------------------
>
> Key: HADOOP-4044
> URL: https://issues.apache.org/jira/browse/HADOOP-4044
> Project: Hadoop Core
> Issue Type: New Feature
> Components: dfs
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: symLink1.patch, symLink1.patch, symLink4.patch,
> symLink5.patch, symLink6.patch, symLink8.patch, symLink9.patch
>
>
> HDFS should support symbolic links. A symbolic link is a special type of file
> that contains a reference to another file or directory in the form of an
> absolute or relative path and that affects pathname resolution. Programs
> which read or write to files named by a symbolic link will behave as if
> operating directly on the target file. However, archiving utilities can
> handle symbolic links specially and manipulate them directly.
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