RFR 10 JDK-8159995: Rename internal Unsafe.compare methods

[Paul Sandoz]

> On 7 May 2017, at 22:30, David Holmes <david.holmes at oracle.com> wrote:
> 
> Hi Ron,
> 
> On 6/05/2017 5:27 AM, Ron Pressler wrote:
>> Hi,
>> Please review the following core/hotspot change:
>> 
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8159995
>> core webrev:
>> http://cr.openjdk.java.net/~psandoz/jdk10/JDK-8159995-unsafe-compare-and-swap-to-set-jdk/webrev/
>> 
>> hotspot webrev:
>> http://cr.openjdk.java.net/~psandoz/jdk10/JDK-8159995-unsafe-compare-and-swap-to-set-hotspot/webrev/
>> 
>> 
>> This change is covered by existing tests.
>> 
>> The following renaming was applied:
>> 
>> - compareAndExchange*Volatile -> compareAndExchange*
>> - compareAndSwap* -> compareAndSet*
> 
> So to clarify this for others, there was confusion surrounding the use of "swap" versus "exchange" when both words mean the same thing effectively, but the "swap" functions return a boolean, while the "exchange" functions return the old value. So we changed "swap" to "set" across the APIs - _except_ for the old /jdk.unsupported/share/classes/sun/misc/Unsafe.java because we can't change its exported API for compatibility reasons.
> 
> Given any "swap(exp, new)" function can be implemented as "exchange(exp, new) == exp" I'm not sure why we have two complete sets of functions all the way through. But I guess that is a different issue. :)
> 

Yes, it might be possible after some careful performance analysis (we might run into some subtle issues).


>> - weakCompareAndSwap* -> weakCompareAndSet*Plain
>> - weakCompareAndSwap*Volatile -> weakCompareAndSet*
>> 
>> At this stage, only method and hotspot intrinsic names were changed;
>> node names were left as-is, and may be handled in a separate issue.
> 
> Overall looks good for libs and hotspot changes.
> 
> One nit I spotted:
> 
> src/java.base/share/classes/java/util/concurrent/atomic/AtomicLong.java
> 
> +     * compareAndSwap for longs. While the intrinsic compareAndSetLong
> 
> compareAndSwap should be compareAndSet
> 
> ---
> 
> All hotspot files need their copyright years updated to 2017 (if not already).
> 
> As there are hotspot changes this must be pushed using JPRT and "-testset hotspot" (but your sponsor should know that :) ).
> 

I do :-)

Paul.