RFR [9]: Better failure output for test/java/util/Arrays/ParallelPrefix.java

[Paul Sandoz]

On Jun 4, 2015, at 4:09 PM, Chris Hegarty <chris.hegarty at oracle.com> wrote:
> On 4 Jun 2015, at 13:37, Paul Sandoz <paul.sandoz at oracle.com> wrote:
> 
>> ...
>> If you wanna go the extra mile it's useful for the data provider to supply a string description argument summarizing the test data.
> 
> Added.
> 

I did not mean:

> +    @DataProvider(name = "intSet")

I meant as a String parameter of the test method, so that some useful summary shows up in the test report. It's not terribly important.


>> You might want to size the arrays in proportion to the parallelism since the threshold is calculated as:
>> 
>> this.threshold =
>>       (p = (hi - lo) / (ForkJoinPool.getCommonPoolParallelism() << 3))
>>       <= MIN_PARTITION ? MIN_PARTITION : p;
>> 
>> So for a large machine with say a parallelism of 2^5 an array size of 2^12 is not sufficient to go above MIN_PARTITION..
> 
> I could be wrong, and I accept your point about sizing as per parallelism, but I think 2^12 should be sufficient for most systems, given MIN_PARTITION = 16. With a parallelism of 2^5, then p will be greater than MIN_PARTITION, no?
> 

Equal to:

  2^12 / (2^5 * 2^3) = 2^12 / 2^8 = 2^4

I think it would be ok to increase this to 2^14.

Paul.