RFR (S) 8150465: Unsafe methods to produce uninitialized arrays

[Aleksey Shipilev]

Hi Jim,

I agree with most of your points.

You are correct that comparing allocateMemory and
allocateUninitializedArray is cumbersome, and I was not trying to
compare these. My comment was about Unsafe at large, notably
peek-and-poke methods that we already have, and can already be used to
leak out data. This is to frame the discussion into "Unsafe is unsafe"
mood.

This is not a regular JDK method. As many other Unsafe methods, it comes
with caveats, and hordes of developers are not the target audience, even
most JDK developers are not the target audience.

The target audience is a tiny group of core library developers who are
(admittedly) well-versed in reading the labels on unsafe methods before
using them. As much as I would like to have a capability-based (and also
fingerprint/retina-scan-based) access control to internal APIs, current
incarnation of Unsafe requires engineering discipline from users.

Unsafe is "off limits" for those who do not understand low-level
mechanics (memory ordering, atomicity requirements, interaction with
runtime, you name it). Unsafe is a special -- perhaps, the only! --
place in JDK where the tradeoff between performance and safety is
heavily tilted towards performance.

Anyone from the huge body of engineers who does not understand this and
uses Unsafe as just another JDK class, could use a really good
talking-to, and probably lots and lots of training.

On 02/26/2016 01:24 PM, Jim Graham wrote:
> I'm seeing a fair amount of hand waving here and not much objective
> analysis of the risks.  It's important to nail down the issues if for
> no other reason than to provide good advice on usage practices in
> our documentation to our internal developers...

Hopefully the updated Javadoc provides enough deterrent from accidental
use. I'd be happy to amend this with even harsher wording, if you tell
me the exact words :)

Webrevs:
  http://cr.openjdk.java.net/~shade/8150465/webrev.jdk.03/
  http://cr.openjdk.java.net/~shade/8150465/webrev.hs.04/

Thanks,
-Aleksey