RFR: 8351443: Improve robustness of StringBuilder [v2]

[Shaojin Wen]

On Thu, 1 May 2025 21:08:29 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Refactor AbstractStringBuilder to maintain consistency among count, coder, and value buffers while the buffer capacity is being expanded and/or inflated from Latin1 to UTF16 representations. 
>> The refactoring pattern is to read and write AbstractStringBuilder fields once using locals for all intermediate values. 
>> Support methods are static, designed to pass all values as arguments and return a value.
>> 
>> The value byte array is reallocated under 3 conditions:
>> - Increasing the capacity with the same encoder
>> - Increasing the capacity and inflation to change the coder from LATIN1 to UTF16
>> - Inflation with the same capacity
>> 
>> Added StressSBTest to exercise public instance methods of StringBuilder.
>
> Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Added missing bugid to tests
>   Applied review suggestions.
>   Added convenience methods to StringLatin1 for 4 and 5 character literals to leverage optimizations for merged stores.
>   Updated missing copyright years.

src/java.base/share/classes/java/lang/StringUTF16.java line 1549:

> 1547:         putChar(value, i++, c4);
> 1548:         putChar(value, i++, c5);
> 1549:         assert(i == end);

We can also use `+1 +2 +3 +4` to replace `++`

        checkBoundsBeginEnd(i, end, value);
        putChar(value, i    , c1);
        putChar(value, i + 1, c2);
        putChar(value, i + 2, c3);
        putChar(value, i + 3, c4);
        putChar(value, i + 4, c5);

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PR Review Comment: https://git.openjdk.org/jdk/pull/24967#discussion_r2071148628