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

[stefan-zobel]

On Fri, 4 Dec 2020 06:50:14 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.

src/java.base/share/classes/jdk/internal/util/ArraysSupport.java line 626:

> 624:      * attempt an array allocation with that length and encounter an OutOfMemoryError.
> 625:      * Of course, regardless of the length value returned from this method, the caller
> 626:      * may encounter OutOfMemoryError if there is insufficient heap to fufill the request.

typo in line 626: fufill -> fulfill

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