Long chains created by direct Buffer::slice

[Florian Weimer]

* Paul Sandoz:

> I created this issue:
>
>   https://bugs.openjdk.java.net/browse/JDK-8208362

Thanks.

> The suggested fix requires a tweak though since an instance of a
> DirectBuffer interface is passed. This is required because views
> over direct ByteBuffers can be created.

Noticed that as well.

> diff -r 448cd909c9e2 src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template
> --- a/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template	Thu Jul 26 11:53:59 2018 -0700
> +++ b/src/java.base/share/classes/java/nio/Direct-X-Buffer.java.template	Thu Jul 26 16:46:20 2018 -0700
> @@ -194,7 +194,8 @@
>  #if[byte]
>          cleaner = null;
>  #end[byte]
> -        att = db;
> +        Object attachment = db.attachment();
> +        att = (attachment == null ? db : attachment);

This is essentially what I put through jtreg (jdk_core), without any
obvious issues, but I had not time yet to file a bug and create a
webrev.

The parenthesis seem unnecessary.  If this is an official JDK coding
style, it is not widely used.