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https://issues.apache.org/jira/browse/HDFS-9924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15317858#comment-15317858
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Jitendra Nath Pandey commented on HDFS-9924:
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The features are not played or experimented with if they are in a feature
branch. No one will use if it is not part of a release, or at least in a
release branch or trunk.
The best way to actually harden an API is to have downstream users use them and
provide feedback. @Unstable was defined for exactly the same purpose.
As suggested by [~steve_l] earlier, if it helps an additional annotation
@Experimental can be created to more strongly highlight the
unstable/experimental nature of the API.
The current implementation is not a user facing API therefore it will have to
be modified when final API is decided in HADOOP-12910.
bq. ... figuring a general approach for async'ing the Filesystem.
There is a proposal on HADOOP-12910 and lets have a discussion around that, to
ensure right API gets committed.
bq ... Retrofitting callback on Future,
I agree it is not a good idea. I think CompletableFuture in jdk8 seems like a
good choice. I am leaning to support CompletableFuture in trunk, and if its too
hard to mimic in branch-2, don't expose a user facing API in branch-2 at all.
Users in branch-2 can use the current unstable/experimental version in
{{DistributedFileSystem}} to try out. Since CompletableFuture implements
Future, it will still not be incompatible in trunk, although we don't guarantee
that.
> [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
> Attachments: AsyncHdfs20160510.pdf
>
>
> 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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