Value type sorting

[Remi Forax]

Hi Doug,
the example of CVal in CVSorter is weird,

 * <pre> {@code
 * __ByValue class CVal {
 *   final long field1;
 *   final long field2;
 *   public CVal(long f2, long f2) { field1 = f1; field2 = f2; }
 *   public int compareTo(CVal b) {
 *       return (field1 < b.field1) ? -1 : (field1 == b.field1) ? 0 : 1;
 *   }
 * }}</pre>

why do you have two long fields instead of one, it doesn't seem to be a fair comparison.
Also, your constructor is weird (f2 is defined twice).

Rémi

----- Mail original -----
> De: "Doug Lea" <dl at cs.oswego.edu>
> À: "valhalla-dev" <valhalla-dev at openjdk.java.net>
> Envoyé: Mercredi 8 Août 2018 20:33:01
> Objet: Value type sorting

> I've been exploring sorting algorithms (mainly parallel but also
> sequential) that should apply well to value types. Even though Valhalla
> is not yet at a state where you can use generic by-value Comparables,
> I've been trying things out by manually plugging in various types, in
> part to scope out future issues. Sorting is the most famous example of a
> problem for which no algorithm is always best. Among other things,
> performance varies with element comparison vs copying cost, parallelism
> support, workspace overhead, and trade-offs of average vs worst case
> behavior. I placed a snapshot of the current Goldilocks candidate
> balancing these for value types at:
>  http://gee.cs.oswego.edu/dl/wwwtmp/CVSorter.java
> The internal documentation describes some of the algorithmic choices.
> As the instruction near the top indicate, for now you need to plug in
> any __ByValue class named "CVal". This compiles and runs using current
> (build zero) early access (http://jdk.java.net/valhalla/).
> 
> Just for comparison, there's also an otherwise identical version for
> long[] arrays at:
>  http://gee.cs.oswego.edu/dl/wwwtmp/LongSorter.java
> When using a __ByValue type just emulating a single long, CVSorter seems
> to be only 5% or so slower than LongSorter sorting 100 million elements,
> which is pretty good for using something labeled build zero. But
> CVSorter also works well with various small or medium-sized value types.
> 
> Any feedback would be welcome. It would be especially nice to hear from
> anyone who has actual data and types that need sorting. There are a lot
> of synthetic loads available (it does well on most), but having some
> actual cases that anyone might be dealing with in the future would be
> helpful.
> 
> -Doug