RFR: 8351443: Improve robustness of StringBuilder [v5]

[Jaikiran Pai]

On Mon, 5 May 2025 17:32:19 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:
> 
>   Refactor to consistently use `isLatin1(coder)` within AbstractStringBuilder.

src/java.base/share/classes/java/lang/AbstractStringBuilder.java line 277:

> 275:                 // copy all bytes to new larger buffer
> 276:                 value = Arrays.copyOf(value,
> 277:                         newCapacity(value, newCoder, minimumCapacity) << newCoder);

Would this benefit with an `assert` to verify that the new buffer length being proposed is not lesser than the current buffer's length (thus truncating content). Something like:


// copy all bytes to new larger buffer
int newLen = newCapacity(value, newCoder, minimumCapacity) << newCoder;
assert newLen >= value.length : "bad new length " + newLen + " for buffer's length " + value.length; 
value = Arrays.copyOf(value, newLen);

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/24967#discussion_r2074546636