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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (YARN-679) add an entry point that can start any Yarn service
Date Fri, 06 Jun 2014 16:14:02 GMT

     [ https://issues.apache.org/jira/browse/YARN-679?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Steve Loughran updated YARN-679:

    Attachment: YARN-679-002.patch

This (big) patch provides the service launcher with 
# a {{ServiceLauncher}} class to load and execute any service
# a new {{LaunchableService extends Service}} interface that adds two methods: {{bindArgs()}}
and {{execute()}}, to bind the CLI args and to execute the service. This improves service
integration with the launcher, *but is not mandatory*. Any service with an empty or string
constructor can be launched. 
# Signal hooking for best-effort shutdown
# an exception handling model which allows any exception to generate a return code.
# a standard set of return codes {{LauncherExitCodes}}
# changes to ExitUtil to improve its ability to exit with given exit codes and messages.
# lots and lots of tests
# lots and lots of javadocs.

The javadocs provide the most information; after a {{mvn javadoc:javadoc}} run, look in {{hadoop-common-project/hadoop-common/target/site/api/org/apache/hadoop/service/launcher/package-summary.html}}

This is the service launcher we've been using for 8+ months, putting into hadoop common has
consisted mainly of tests & javadocs, with some (long desired) enhancements to exit code
handling (HADOOP-9626).

I have not -yet- made any changes to CLI processing. So far it doesn't do as much as tool
runner. All it does is scan the CLI args list for {{--conf filename}} pairs, extracting configuration
files from them and,  after testing, adds it to the configuration used to initialize the service.

If we want more, rather than try and get the (outdated) {{GenericOptionsParser}} to do the
parsing, I'd prefer to write a JCommander-based alternative, with (most) of the same arguments,
but more usable and extensible, and with its own tests. I've been using JCommander and an
familiar with its features and quirks now.

> add an entry point that can start any Yarn service
> --------------------------------------------------
>                 Key: YARN-679
>                 URL: https://issues.apache.org/jira/browse/YARN-679
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: api
>    Affects Versions: 2.4.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: YARN-679-001.patch, YARN-679-002.patch
> There's no need to write separate .main classes for every Yarn service, given that the
startup mechanism should be identical: create, init, start, wait for stopped -with an interrupt
handler to trigger a clean shutdown on a control-c interrrupt.
> Provide one that takes any classname, and a list of config files/options

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