RFR: 8247373: ArraysSupport.newLength doc, test, and exception message [v2]

[Paul Sandoz]

On Tue, 8 Dec 2020 06:14:35 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> This rewrites the doc of ArraysSupport.newLength, adds detail to the exception message, and adds a test. In addition to some renaming and a bit of refactoring of the actual code, I also made two changes of substance to the code:
>> 
>> 1. I fixed a problem with overflow checking. In the original code, if oldLength and prefGrowth were both very large (say, Integer.MAX_VALUE), this method could return a negative value. It turns out that writing tests helps find bugs!
>> 
>> 2. Under the old policy, if oldLength and minGrowth required a length above SOFT_MAX_ARRAY_LENGTH but not above Integer.MAX_VALUE, this method would return Integer.MAX_VALUE. That doesn't make any sense, because attempting to allocate an array of that length will almost certainly cause the Hotspot to throw OOME because its implementation limit was exceeded. Instead, if the required length is in this range, this method returns that required length.
>> 
>> Separately, I'll work on retrofitting various call sites around the JDK to use this method.
>
> Stuart Marks has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix typo, clarify asserts disabled, test prefGrowth==0

Marked as reviewed by psandoz (Reviewer).

src/java.base/share/classes/jdk/internal/util/ArraysSupport.java line 616:

> 614:      * greater than the soft maximum but does not exceed Integer.MAX_VALUE, the minimum
> 615:      * required length is returned. Otherwise, the minimum required length exceeds
> 616:      * Integer.MAX_VALUE, which can never be fulfilled, so this method throws OutOfMemoryError.

I think you can simplify with:

Suggestion:

     * If the preferred length exceeds the soft maximum, we use the minimum growth
     * amount. The minimum required length is determined by adding the minimum growth
     * amount to the current length. 
     * If the minimum required length exceeds Integer.MAX_VALUE, then this method 
     * throws OutOfMemoryError. Otherwise, this method returns the soft maximum or
     * minimum required length, which ever is greater.

Then i think it follows that `Math.max` can be used in the implementation.

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PR: https://git.openjdk.java.net/jdk/pull/1617