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https://issues.apache.org/jira/browse/KAFKA-1008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13739197#comment-13739197
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Jay Kreps commented on KAFKA-1008:
----------------------------------
Hey Elizabeth, thanks for the patch.
Two issues.
The first is that I think that instanceof check will actually throw an
exception on a non-sun jvm. See the experiment below and see what you think.
The second issue is actually a more subtle thing. Currently the synchronization
is really just for changes to the buffer, the read-access are lock-free (which
is good). My concern is what happens if we force clean a buffer while a read is
occurring? Not sure if this can happen or not, but I think we need to somehow
be sure it can't.
Here was my test:
$ cat /tmp/code/Test.java
import test.MyTest;
public class Test {
public static void main(String[] args) {
Object o = new Object();
if(o instanceof MyTest)
System.out.println("Hello");
}
}
$ cat /tmp/code/test/MyTest.java
package test;
public class MyTest {
}
I do
javac /tmp/code/test/MyTest.java
javac -cp /tmp/code /tmp/code/Test.java
rm /tmp/code/test/MyTest.class
$ java -cp /tmp/code Test
Exception in thread "main" java.lang.NoClassDefFoundError: test/MyTest
at Test.main(Test.java:6)
Caused by: java.lang.ClassNotFoundException: test.MyTest
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
... 1 more
We also can't really be too sure what kind of exceptions clean() might throw.
> Unmap before resizing
> ---------------------
>
> Key: KAFKA-1008
> URL: https://issues.apache.org/jira/browse/KAFKA-1008
> Project: Kafka
> Issue Type: Bug
> Components: core, log
> Affects Versions: 0.8
> Environment: Windows, Linux, Mac OS
> Reporter: Elizabeth Wei
> Assignee: Jay Kreps
> Labels: patch
> Fix For: 0.8
>
> Attachments: unmap-v2.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> While I was studying how MappedByteBuffer works, I saw a sharing runtime
> exception on Windows. I applied what I learned to generate a patch which uses
> an internal open JDK API to solve this problem.
> Following Jay's advice, I made a helper method called tryUnmap().
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