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From "Michel Tourn (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-488) Change ToolBase.doMain() to return a status code
Date Tue, 29 Aug 2006 16:40:23 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-488?page=comments#action_12431289 ] 
            
Michel Tourn commented on HADOOP-488:
-------------------------------------

System.exit is also bad bec. it is "non-composable": 
it gets in the way of  tools that try to run other tools in the same JVM (like ant and junit
and pot. TaskRunner)

However this proposal is not about using System.exit more than before. It is about exposing
additional information, should you choose to use System.exit.

Usage as before: 

use doMain() from other Java code, like integration tests. This does not call System.exit()

use main() from a top-level application that integrates with shell tools: these tools only
understand status codes, not Java exceptions. This calls System.exit()

Now in both cases, the caller has access to the status code.

+1







> Change ToolBase.doMain() to return a status code
> ------------------------------------------------
>
>                 Key: HADOOP-488
>                 URL: http://issues.apache.org/jira/browse/HADOOP-488
>             Project: Hadoop
>          Issue Type: Improvement
>    Affects Versions: 0.6.0
>            Reporter: Andrzej Bialecki 
>             Fix For: 0.6.0
>
>
> I propose to change the signature of ToolBase.doMain from this:
>     public final void doMain(Configuration conf, String[] args) throws Exception;
> to this:
>     public final int doMain(Configuration conf, String[] args) throws Exception;
> and then change main() methods of all classes that use ToolBase.doMain to call System.exit(code),
where "code" is this return value from doMain(). All command-line tools, which still call
main() methods of other tools, should be converted to use doMain() and return exit codes properly.
> The main reason for this change is that returning varying exit codes is required for
proper operation of shell scripts, especially differing between code == 0 (normal exit) and
code != 0 (error exit).
> Additionally, current implementation of doMain() already gets the return code, it just
silently discards it (ToolBase.java:184).

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