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From "Zhanwei Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7207) libhdfs3 should not expose exceptions in public C++ API
Date Thu, 09 Oct 2014 03:08:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14164638#comment-14164638
] 

Zhanwei Wang commented on HDFS-7207:
------------------------------------

Not exposing exceptions in public APIs in libhdfs3 is good to improve the ABI compatibility
and make c\+\+ interface is more useful. [~wheat9]'s suggestion is pretty good.

I do not think it is necessary to add additional C\+\+ interface for libhdfs and libwebhdfs.


1) Both libhdfs and libwebhdfs are implemented in C, and all C and C\+\+ application can use
C interface.
2) libhdfs3 also implements the C interface, Any existing application which is using libhdfs
and libwebhdfs can easily switch to libhdfs3.
3) New application usually prefer C interface instead of C\+\+ because C interface is more
stable.
4) If new application decides to use libhdfs3, which means it has no requirement of access
S3 and other features not supported in libhdfs or libwebhdfs. Therefore it will not switch
back to libhdfs or libwebhdfs. 
5) If new application wants to use the feature in libhdfs3 but not implemented yet (like encryption),
it can use libhdfs or libwebhdfs with C interface and switch to libhdfs3 later. 

So, it is more important to implement compatible C interface in libhdfs3 instead of adding
additional C\+\+ interface to libhdfs and libwebhdfs.

I think [~wheat9]'s purpose of creating this jira is to remove the exception from libhdfs3's
C\+\+ API to make libhdfs3's C\+\+ API more useful.
 

> libhdfs3 should not expose exceptions in public C++ API
> -------------------------------------------------------
>
>                 Key: HDFS-7207
>                 URL: https://issues.apache.org/jira/browse/HDFS-7207
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Haohui Mai
>            Assignee: Colin Patrick McCabe
>            Priority: Blocker
>         Attachments: HDFS-7207.001.patch
>
>
> There are three major disadvantages of exposing exceptions in the public API:
> * Exposing exceptions in public APIs forces the downstream users to be compiled with
{{-fexceptions}}, which might be infeasible in many use cases.
> * It forces other bindings to properly handle all C++ exceptions, which might be infeasible
especially when the binding is generated by tools like SWIG.
> * It forces the downstream users to properly handle all C++ exceptions, which can be
cumbersome as in certain cases it will lead to undefined behavior (e.g., throwing an exception
in a destructor is undefined.)



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