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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-17872) The MSLABImpl generates the invaild cells when unsafe is not availble
Date Thu, 06 Apr 2017 16:42:41 GMT

    [ https://issues.apache.org/jira/browse/HBASE-17872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15959250#comment-15959250
] 

stack commented on HBASE-17872:
-------------------------------

Seems a pity making runtime pay the price of test-time convenience. Volatile reads are way
more expensive than a local cache read. The UNSAFE_AVAIL check is called frequently.

Make UNSAFE_AVAIL a final static?

Then it becomes how to change a static final setting at test time. Reflection? A delegating
class that makes use of a subclass of  ByteBufferUtils ? Could move the test clutter of detectAvailabilityOfUnsafe
and disableUnsafe out of this vital class and into this new test class.

> The MSLABImpl generates the invaild cells when unsafe is not availble
> ---------------------------------------------------------------------
>
>                 Key: HBASE-17872
>                 URL: https://issues.apache.org/jira/browse/HBASE-17872
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Chia-Ping Tsai
>            Assignee: Chia-Ping Tsai
>            Priority: Critical
>             Fix For: 2.0.0
>
>         Attachments: HBASE-17872.v0.patch, HBASE-17872.v1.patch, HBASE-17872.v2.patch
>
>
> We will get the wrong position of buffer in multithreaded environment, so the method
makes the invalid cell in MSLAB.
> {noformat}
>   public static int copyFromBufferToBuffer(ByteBuffer in, ByteBuffer out, int sourceOffset,
>       int destinationOffset, int length) {
>     if (in.hasArray() && out.hasArray()) {
>       // ...
>     } else if (UNSAFE_AVAIL) {
>       // ...
>     } else {
>       int outOldPos = out.position();
>       out.position(destinationOffset);
>       ByteBuffer inDup = in.duplicate();
>       inDup.position(sourceOffset).limit(sourceOffset + length);
>       out.put(inDup);
>       out.position(outOldPos);
>     }
>     return destinationOffset + length;
>   }
> {noformat}



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