[
https://issues.apache.org/jira/browse/CASSANDRA-12381?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15407944#comment-15407944
]
Robert Stupp edited comment on CASSANDRA-12381 at 8/4/16 3:31 PM:
------------------------------------------------------------------
[link to the netty issue|https://github.com/netty/netty/issues/5629]
A direct buffer with an array feels very weird. At least with the current state
of OpenJDK/Oracle Java. I don't get how a direct buffer (off-heap) with an
array (on-heap) would be consistent - that's why I mentioned it is not safe.
On-heap objects can move (copied) - direct buffers must not move as these can
be used by the OS for example for I/O. Maybe that is not true for the Dalvik VM
/ Android.
However, adding a {{!isDirect()}} (i.e. {{hasArray()}} --> {{!isDirect &&
hasArray()}}) feels more safe - maybe just in trunk since if cannot be an issue
now.
was (Author: snazy):
[link to the netty issue|https://github.com/netty/netty/issues/5629]
A direct buffer with an array feels very weird. At least with the current state
of OpenJDK/Oracle Java. I don't get how a direct buffer (off-heap) with an
array (on-heap) would be consistent - that's why I mentioned it is not safe.
On-heap objects can move (copied) - direct buffers must not move as these can
be used by the OS for example for I/O. Maybe that is not true for the Dalvik VM
/ Android.
However, adding a {{!isDirect()}} feels more safe - maybe just in trunk since
if cannot be an issue now.
> Verify use of ByteBuffer.hasArray() in whole code base
> ------------------------------------------------------
>
> Key: CASSANDRA-12381
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12381
> Project: Cassandra
> Issue Type: Bug
> Reporter: Robert Stupp
> Assignee: Robert Stupp
> Priority: Minor
> Fix For: 3.0.x
>
>
> As [noted
> here|https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html#allocateDirect-int-],
> a direct {{ByteBuffer}} can have a backing array.
> If a direct {{ByteBuffer}} has a backing array, we should not make any
> assumption on how it is actually used.
> This ticket is about to check whether uses of {{ByteBuffer.hasArray()}} need
> to be replaced with {{ByteBuffer.isDirect()}}.
> (With CASSANDRA-11870 however, there is no way that such a direct
> {{ByteBuffer}} has a backing array.)
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
