RFR: 8341566: Add Reader.of(CharSequence) [v11]

[Eirik Bjørsnøs]

On Sat, 12 Oct 2024 07:47:56 GMT, Markus KARG <duke at openjdk.org> wrote:

>> This Pull Requests proposes an implementation for [JDK-8341566](https://bugs.openjdk.org/browse/JDK-8341566): Adding the new method `public static Reader Reader.of(CharSequence)` will return an anonymous, non-synchronized implementation of a `Reader` for each kind of `CharSequence` implementation. It is optimized for `String`, `StringBuilder`, `StringBuffer` and `CharBuffer`.
>> 
>> In addition, this Pull Request proposes to replace the implementation of `StringReader` to become a simple synchronized wrapper around `Reader.of(CharSequence)` for the case of `String` sources. To ensure correctness, this PR...
>> * ...simply moved the **original code** of `StringBuilder` to become the de-facto implementation of `Reader.of()`, then stripped synchronized from it on the left hand, but kept just a synchronized wrapper on the right hand. Then added a `switch` for optimizations within the original code, at the exact location where previously just an optimization for `String` lived in.
>> * ...added tests for all methods (`Of.java`), and applied that test upon the modified `StringBuilder`.
>> 
>> Wherever new JavaDocs were added, existing phrases from other code locations have been copied and adapted, to best match the same wording.
>
> Markus KARG has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert 'inc should be faster than add on most CPUs'

src/java.base/share/classes/java/io/Reader.java line 214:

> 212:                             cbuf[off + i] = cs.charAt(next + i);
> 213:                     }
> 214:                 }

Just a drive-by observation, not for this PR to handle:

If four out of five `CharSequence` implementations in the JDK include fast-path methods for copying char ranges into an output buffer, perhaps it is time to introduce `CharSequence::getChars` as a default method? 

That way, code like this wouldn't need to special-case for the known fast-paths, and external implementations could also join the party.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21371#discussion_r1799981701