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https://issues.apache.org/jira/browse/HDFS-9924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15187273#comment-15187273
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Chris Nauroth commented on HDFS-9924:
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[~bobhansen], thank you for the comment. It's an interesting thought. I was
going to suggest providing a model of futures + promises as a further
enhancement to be done later. That would give applications an elegant model
for chaining together a sequence of async operations that have specific
ordering dependencies.
Our main motivation right now is the Hive use case I described in my last
comment. Futures alone are a good fit for that, hence the motivation to defer
consideration of promises to a later enhancement, outside the scope of the
current issue.
> [umbrella] Asynchronous HDFS Access
> -----------------------------------
>
> Key: HDFS-9924
> URL: https://issues.apache.org/jira/browse/HDFS-9924
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: fs
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Xiaobing Zhou
>
> This is an umbrella JIRA for supporting Asynchronous HDFS Access.
> Currently, all the API methods are blocking calls -- the caller is blocked
> until the method returns. It is very slow if a client makes a large number
> of independent calls in a single thread since each call has to wait until the
> previous call is finished. It is inefficient if a client needs to create a
> large number of threads to invoke the calls.
> We propose adding a new API to support asynchronous calls, i.e. the caller is
> not blocked. The methods in the new API immediately return a Java Future
> object. The return value can be obtained by the usual Future.get() method.
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