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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-3628) Add a lifecycle interface for Hadoop components: namenodes, job clients, etc.
Date Wed, 25 Jun 2008 10:01:44 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3628?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Steve Loughran updated HADOOP-3628:

    Attachment: AbstractHadoopComponent.java

OK, an abstract class like the one attached is easily done.

Some thoughts.

1. should the terminate() operation return a list of throwables that were caught during termination?
That way, rather than just log problems on shutdown, whatever initiates the shutdown can deal
with them by logging/rethrowing, etc.

2. Is the set of states right? do we want a STARTING state that components enter until they
consider themselves live? 

3. The class is a base class of Configurable. I plan to move the code that reads in the configuration
from the constructors into init(); that way subclasses can do tricks such as manipulate the
configuration before it is read. 

4. Should the base methods be synchronized? The alternative is to leave that to the subclasses,
as appropriate. In our experience, having the terminate() option non-synchronized is good
to avoid deadlocks; for the others, synchronized is generally good.

5. The base class can verify the system is in the right state, throwing exceptions if not.

6. I'll add a HadoopException that extends IOException too.

7. is org.apache.hadoop.conf the right package? 

Test-wise, we can add tests that check this, with a mock object that can be configured to
fail in any of the method calls, so as to stress any container

> Add a lifecycle interface for Hadoop components: namenodes, job clients, etc.
> -----------------------------------------------------------------------------
>                 Key: HADOOP-3628
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3628
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs, mapred
>    Affects Versions: 0.19.0
>            Reporter: Steve Loughran
>         Attachments: AbstractHadoopComponent.java
> I'd like to propose we have a standard interface for hadoop components, the things that
get started or stopped when you bring up a namenode. currently, some of these classes have
a stop() or shutdown() method, with no standard name/interface, but no way of seeing if they
are live, checking their health of shutting them down reliably. Indeed, there is a tendency
for the spawned threads to not want to die; to require the entire process to be killed to
stop the workers. 
> Having a standard interface would make it easier for 
>  * management tools to manage the different things
>  * monitoring the state of things
>  * subclassing
> The latter is interesting as right now TaskTracker and JobTracker start up threads in
their constructor; that's very dangerous as subclasses may have their methods called before
they are full initialised. Adding this interface would be the right time to clean up the startup
process so that subclassing is less risky.

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