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Sylvain Lebresne commented on CASSANDRA-12381:
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bq. Strictly, we have some misuses (assuming !hasArray() == direct buffer) for
example in
org.apache.cassandra.io.util.BufferedDataOutputStreamPlus#write(java.nio.ByteBuffer)
You have be careful with logic :). If we get precise, the clearly incorrect
assumption is that {{isDirect()}} implies {{!hasArray()}} (the javadoc is very
explicit on that).
However, It does sound kind of implied (by the doc on {{allocate()}}) that non
direct buffers do always have a backed buffer, and so that {{!hasArray()}} does
imply {{isDirect()}}, which is what we rely on here. To be fair, the one thing
I haven't found is a place that explicitly said that non-direct buffer can
*only* be built by either {{allocate()}} or {{wrap()}} (or some
slicing/duplicate on a non-direct one), so in theory I wouldn't mind updating
that part of the code, but I genuinely don't know what you'd do of a buffer
that doesn't have a backing array but isn't direct either. That is, if you're
only changing {{hasArray()}} to {{!isDirect()}} in that code, you're really
making the exact same assumption the code already does, but it's less explicit
imo. Overall, this code clearly states the assumption it does make, so I think
it's fine.
Again, I'm totally fine fixing the {{isDirect()}} => {{!hasArray()}} assumption
if we ever do it, but that's not an example of that.
> 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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