[jira] [Created] (HADOOP-13716) Add an Eventually class to await eventual completion of lambda expressions

["Steve Loughran (JIRA)" <ji...@apache.org>]

Steve Loughran created HADOOP-13716:
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             Summary: Add an Eventually class to await eventual completion of lambda expressions
                 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


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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