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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 Tue, 19 Dec 2017 14:13:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16296844#comment-16296844
] 

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

Github user dchuyko commented on a diff in the pull request:

    https://github.com/apache/hadoop/pull/291#discussion_r157764279
  
    --- Diff: hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/Shell.java
---
    @@ -89,6 +89,22 @@ public static boolean isJava7OrAbove() {
         return true;
       }
     
    +  private static final boolean IS_JAVA9_OR_ABOVE;
    +  static {
    +    int major = 0;
    +    try {
    +      // 1.8.0 -> 1, 10-ea+30 -> 10, 18.03 -> 18, 11 -> 11 etc.
    +      String version = System.getProperty("java.version");
    +      major = Integer.parseInt(version.split("\\.")[0].split("-")[0]);
    +    } catch (NumberFormatException ignored) {
    +    }
    +    IS_JAVA9_OR_ABOVE = major >= 9;
    +  }
    +
    +  public static boolean isJava9OrAbove() {
    +    return IS_JAVA9_OR_ABOVE;
    +  }
    --- End diff --
    
    Yes, I had exactly the same in mind. Just haven't realized we may now assume 8 as lowest
version. Will it still be true if someone decides to backport the fix to previous Hadoop versions?


> 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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