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https://issues.apache.org/jira/browse/HDFS-9924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15322864#comment-15322864
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stack commented on HDFS-9924:
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bq. This JIRA and the current implementation originally aim to support a basic
async access to HDFS without callback support and without chaining support.
The JIRA is about HDFS async access. There is no exception in the summary nor
description to rule out the basic async callback primitive. You could rule it
out via fiat -- can you even call it an 'async' API if it doesn't do callback?
-- but why not do it right from the get-go. Do it once only too.
bq. When we change to return XxxFuture in the future, it is a backward
compatible change.
You and [~jnp] have said this a few times but for downstreamers, a Future-only
API is not worth engaging with. It means each of us has to build parking
structures to keep the unfinished the Futures in, polling to look for
completions to react too. This is a performance-killer. Been there. Done that.
I like the [~mingma] summary/suggestion with the [~andrew.wang] caveat; revert
and dev in a feature branch against trunk. I know of a few downstreamers that
are interested, myself included, and would be up for helping out. Thanks.
> [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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