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https://issues.apache.org/jira/browse/HDFS-14321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16782214#comment-16782214
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Sahil Takiar commented on HDFS-14321:
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Digging into this some more, I think {{hadoopRzOptions::byteBufferPool}} should
be a global ref. If {{hadoopRzOptionsSetByteBufferPool}} simply created a local
ref to {{hadoopRzOptions::byteBufferPool}} then the reference would be lost
once the porcess execution returned back to Java. By using a global ref, we
ensure that {{byteBufferPool}} does not get garbage collected by the JVM. Since
the {{byteBufferPool}} is expected to live across calls to {{hadoopReadZero}},
using a local ref does not make sense.
This is based on my understanding of the JNI and the difference between local
vs. global references:
http://journals.ecs.soton.ac.uk/java/tutorial/native1.1/implementing/refs.html
I'm not a JNI expert, so my understanding might be off, but this patch fixes
the {{FATAL ERROR}}.
The second part of this patch is to add {{-Xcheck:jni}} to {{LIBHDFS_OPTS}}
when running all the libhdfs ctests. The drawback here is that adding this
pollutes the logs with a bunch of warnings about exception handling (see
above). The benefit is that it ensures we don't make any changes to libhdfs
that would results in more fatal errors. IMO I think we can live with the
extraneous logging, but open to changing this if others feel differently.
> Fix -Xcheck:jni issues in libhdfs, run ctest with -Xcheck:jni enabled
> ---------------------------------------------------------------------
>
> Key: HDFS-14321
> URL: https://issues.apache.org/jira/browse/HDFS-14321
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client, libhdfs, native
> Reporter: Sahil Takiar
> Assignee: Sahil Takiar
> Priority: Major
> Attachments: HDFS-14321.001.patch
>
>
> The JVM exposes an option called {{-Xcheck:jni}} which runs various checks
> against JNI usage by applications. Further explanation of this JVM option can
> be found in:
> [https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/clopts002.html]
> and
> [https://www.ibm.com/support/knowledgecenter/en/SSYKE2_8.0.0/com.ibm.java.vm.80.doc/docs/jni_debug.html].
> When run with this option, the JVM will print out any warnings or errors it
> encounters with the JNI.
> We should run the libhdfs tests with {{-Xcheck:jni}} (can be added to
> {{LIBHDFS_OPTS}}) and fix any warnings / errors. We should add this option to
> our ctest runs as well to ensure no regressions are introduced to libhdfs.
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