[jira] [Commented] (HADOOP-5353) add progress callback feature to the slow FileUtil operations with ability to cancel the work

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

    [ https://issues.apache.org/jira/browse/HADOOP-5353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15323082#comment-15323082 ] 

Steve Loughran commented on HADOOP-5353:
----------------------------------------

Quick review

* please don't change indentation needlessly, do follow hadoop code layout rules, import wildcard policy etc.
* {{FileUtil.copy()}} should throw FileNotFoundException when things aren't there. 
* line 482 Have a look inside FileSystem.exists() and you'll see why you could cut that clause and just go with the else clause
* 499. Exception.toString() over Exception.getMessage
* line 529. I think there should be better handling than "false" if the destination dir couldn't be created, given its
the complete failure of the operation. 
* like 546 & elsewhere. Use try-with-resources now the codebase is Java 7+



 {{CommandWithDestination}}: {{TargetFileSystem}} supports try-with-resources cleanup too. Same for {{writeStreamToFile}}
 
 

 regarding the test,
 
 
# look at [ https://github.com/steveloughran/formality/blob/master/styleguide/styleguide.md ] for how to write good asserts. 
# In particular, assertTrue and assertFalse must have messages, and if some probe of exception value/state fails, just throw that exception again.
# There's lots of code in {{ContractTestUtils}} for writing/reading/probing filesystems



> add progress callback feature to the slow FileUtil operations with ability to cancel the work
> ---------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-5353
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5353
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>    Affects Versions: 0.21.0
>            Reporter: Steve Loughran
>            Assignee: Pranav Prakash
>            Priority: Minor
>         Attachments: HADOOP-5353.000.patch, HADOOP-5353.001.patch
>
>
> This is something only of relevance of people doing front ends to FS operations, and as they could take the code in FSUtil and add something with this feature, its a blocker to none of them. 
> Current FileUtil.copy can take a long time to move large files around, but there is no progress indicator to GUIs, or a way to cancel the operation mid-way, j interrupting the thread or closing the filesystem.
> I propose a FileIOProgress interface to the copy ops, one that had a single method to notify listeners of bytes read and written, and the number of files handled.
> {code}
> interface FileIOProgress {
>  boolean progress(int files, long bytesRead, long bytesWritten);
> }
> The return value would be true to continue the operation, or false to stop the copy and leave the FS in whatever incomplete state it is in currently. 
> it could even be fancier: have  beginFileOperation and endFileOperation callbacks to pass in the name of the current file being worked on, though I don't have a personal need for that.
> GUIs could show progress bars and cancel buttons, other tools could use the interface to pass any cancellation notice upstream.
> The FileUtil.copy operations would call this interface (blocking) after every block copy, so the frequency of invocation would depend on block size and network/disk speeds. Which is also why I don't propose having any percentage done indicators; it's too hard to predict percentage of time done for distributed file IO with any degree of accuracy.



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