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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15033) Use java.util.zip.CRC32C for Java 9 and above
Date Thu, 21 Dec 2017 15:02:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16300132#comment-16300132
] 

ASF GitHub Bot commented on HADOOP-15033:
-----------------------------------------

Github user dchuyko commented on the issue:

    https://github.com/apache/hadoop/pull/291
  
    Ok, I changed the patch according to the review.
    
    1. There's now isJavaSpecAtLeast() in Shell. This is a part I like.
    
    2. In DataChecksum there are now: racy state "useJava9Crc32C" which is set to the above
by default and falls to false on error. New Java9Crc32CFactory now holds static method handles
stuff to let it be initialized on first usage. And there is now also LOG to possibly log errors
that never happen. To me it looks probably like too much meat for code that won't be called
ever. And in case of NOP logger no one will see the error if it happens still. From the other
hand all that may look more safe.


> Use java.util.zip.CRC32C for Java 9 and above
> ---------------------------------------------
>
>                 Key: HADOOP-15033
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15033
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: performance, util
>    Affects Versions: 3.0.0
>            Reporter: Dmitry Chuyko
>              Labels: Java9, common, jdk9
>         Attachments: HADOOP-15033.001.patch, HADOOP-15033.001.patch, HADOOP-15033.002.patch,
HADOOP-15033.003.patch, HADOOP-15033.003.patch, HADOOP-15033.004.patch
>
>
> java.util.zip.CRC32C implementation is available since Java 9.
> https://docs.oracle.com/javase/9/docs/api/java/util/zip/CRC32C.html
> Platform specific assembler intrinsics make it more effective than any pure Java implementation.
> Hadoop is compiled against Java 8 but class constructor may be accessible with method
handle on 9 to instances implementing Checksum in runtime.



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