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https://issues.apache.org/jira/browse/HADOOP-13716?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Steve Loughran updated HADOOP-13716:
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    Attachment: HADOOP-13716-001.patch

Patch 001.

The production code is Java7+; the tests are of both java7 and java 8 
code...for backporting to java 8 you'd just pull those test cases with the word 
"lambda" in.

Because this is needed to improve some of the FS contract tests, they should be 
a PoC that the API works —I'd be targeting Java 7 there.

> Add an Eventually class to for tests to await eventual completion of lambda 
> expressions/test clauses
> ----------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-13716
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13716
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: test
>    Affects Versions: 2.8.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: HADOOP-13716-001.patch
>
>
> To make our tests robust against timing problems and eventual consistent 
> stores, we need to do more spin & wait for state.
> We have some code in {{GenericTestUtils.waitFor}} to await a condition being 
> met, but the predicate it calls doesn't throw exceptions, there's no way for 
> a probe to throw an exception, and all you get is the eventual "timed out" 
> message. 
> We can do better, and in closure-ready languages (scala & scalatest, groovy 
> and some slider code) we've examples to follow. Some of that work has been 
> reimplemented slightly in {{S3ATestUtils.eventually}}
> I propose adding a class in the test tree, {{Eventually}} to be a 
> successor/replacement for these.
> # has an eventually/waitfor operation taking a predicate that throws an 
> exception
> # has an "evaluate" exception which tries to evaluate an answer until the 
> operation stops raising an exception. (again, from scalatest)
> # plugin backoff strategies (from Scalatest; lets you do exponential as well 
> as linear)
> # option of adding a special handler to generate the failure exception (e.g. 
> run more detailed diagnostics for the exception text, etc).
> # be Java 8 lambda expression friendly
> # be testable and tested itself.



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