RFR: 8358533: Improve performance of java.io.Reader.readAllLines [v6]

[Roger Riggs]

On Fri, 27 Jun 2025 15:03:05 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Replaces the implementation `readAllCharsAsString().lines().toList()` with reading into a temporary `char` array which is then processed to detect line terminators and copy non-terminating characters into strings which are added to the list.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8358533: Test change accidentally omitted from previous commit

src/java.base/share/classes/java/io/Reader.java line 477:

> 475:                     boolean isCR = (cb[term] == '\r');
> 476:                     if (isCR || !(skipLF && term == pos)) {
> 477:                         // line terminator is a CR or an LF just after a CR

Suggestion:

                        // line terminator is a CR or an LF not after a CR

src/java.base/share/classes/java/io/Reader.java line 484:

> 482:                             lines.add(new String(cb, pos, term - pos));
> 483:                         }
> 484:                     }

This might be a good place to check for NL after CR and efficiently skip it.  (Common on Windows).
It could save a cycle through the `while (pos < limit)` loop just to ignore the LF. (Except for the case of CR at the end of the buffer.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/25863#discussion_r2172300601
PR Review Comment: https://git.openjdk.org/jdk/pull/25863#discussion_r2172307928