RFR 8146458 Improve exception reporting for Objects.checkIndex/checkFromToIndex/checkFromIndexSize

[Paul Sandoz]

Thanks for the feedback. Updated:

  http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8146458-checkIndex-exception-reporting/webrev/
  http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8146458-checkIndex-exception-reporting/specdiff/overview-summary.html

Changes:

- refer to “exception factory function”

- renamed rangeCheckExceptionMapper to outOfBoundsExceptionFactory. Tweaked the documentation and added an api note for clarity.

- tests for String/ArrayIOOBE, and uniform checking of expected exception message in all cases


> On 16 Jan 2016, at 08:36, John Rose <john.r.rose at oracle.com> wrote:
> 
> On Jan 15, 2016, at 2:43 PM, Stuart Marks <stuart.marks at oracle.com> wrote:
>> 
>> 
>> I think, in order to avoid introducing new functional interfaces, this information is funneled into a single varargs call, which has to use Integer boxes, because it then wraps its args into a List (thanks for using the new List factory!), which then has to unpack the list and check its length against the number of arguments for the particular message kind.
> 
> And that's before String.format does a bunch more steps of the same kind, including boxing and varargs. And then the exception creation itself walks the entire thread stack. Micro-optimization is hopeless.
> 
> But it doesn't matter because it's all on the slow path.
> 

Yes. FWIW the implementation also avoids any varargs call for the main check methods to keep the method size small (we could use @ForceInline instead, but i would prefer to use that for cases where it is really needed).


>> I understand that this is the "slow" exception-throwing path, but my sense is still that this ought to be made simpler. Perhaps the scope of what it's trying to accomplished should be reduced, if that helps things.
> 
> Simpler would be good but I don't see it any simpler, yet.
> 

Me neither, any simpler and the generality is lost. Arguably there is actually quite a simple rule underlying this: the arguments to the factory function take on a form that is very similar to those required for a reflective look up and invocation:

  Objects.class.getMethod(checkKind, List.nCopies(args.size(), int.class).toArray()).
    invoke(null, args.toArray())

Paul.

> Do give it some thought!
>