RFR: 8299807: newStringNoRepl should avoid copying arrays for ASCII compatible charsets

[Glavo]

On Fri, 27 Jan 2023 16:04:41 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> This is the javadoc of `JavaLangAccess::newStringNoRepl`:
>> 
>> 
>>     /**
>>      * Constructs a new {@code String} by decoding the specified subarray of
>>      * bytes using the specified {@linkplain java.nio.charset.Charset charset}.
>>      *
>>      * The caller of this method shall relinquish and transfer the ownership of
>>      * the byte array to the callee since the later will not make a copy.
>>      *
>>      * @param bytes the byte array source
>>      * @param cs the Charset
>>      * @return the newly created string
>>      * @throws CharacterCodingException for malformed or unmappable bytes
>>      */
>> 
>> 
>> It is recorded in the document that it should be able to directly construct strings with parameter byte array to reduce array allocation.
>> 
>> However, at present, `newStringNoRepl` always copies arrays for UTF-8 or other ASCII compatible charsets.
>> 
>> This PR fixes this problem.
>
> It seems odd that the benchmark seems slower for smaller files; can you suggest why that might be?
> I'd expect the size distribution for Files.readString to be biased toward the smaller files.
> Can you repeat the benchmark using the default file system.  OS file caching should eliminate the disk speed effects.

@RogerRiggs I have revised it according to your suggestion. Can you have a look again?

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PR: https://git.openjdk.org/jdk/pull/12119