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Sylvain Lebresne commented on CASSANDRA-12381:
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bq. A direct buffer with an array feels very weird. At least with the current
state of OpenJDK/Oracle Java.
Maybe, but the javadoc is the spec, not our current knowledge of any specific
implementation or our personal sentiment of what the spec should be. My reading
of the Netty ticket (thanks for the link) is that Netty was assuming
{{hasArray()}} => {{isDirect()}}, which is clearly a violation of the spec, but
they don't seem to have had any problem accessing the backing buffer of a
direct buffer. And again, the spec seems pretty clear to me on the fact that
*if* a direct buffer returns {{true}} for {{hasArray()}} (no matter how rare
this is), then the array returned by {{array}} should be safe to use. And as
far as I can tell, we always use {{hasArray}} properly, as a guard before
calling {{array}}, and I strongly think we should keep {{hasArray()}} for this,
since that's much more explicit. Of course, if there is a few places where we
misuse {{hasArray()}} as a mean to know if the buffer is not direct, then we
should fix those, but I doubt we do that much, if ever (the Netty case is
pretty special here).
> 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.)
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