RFR: 8358533: Improve performance of java.io.Reader.readAllLines

[Brian Burkhalter]

On Wed, 18 Jun 2025 00:04:37 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.

The throughput of the implementation as measured by the included benchmark appears to hover around 13% greater than that of the existing method. The updated method should also have a smaller memory footprint for streams of non-trivial length as it does not first create a single intermediate `String` containing all lines in the stream. Instead it uses a `char` array of size 8192 and a `StringBuilder` whose maximum length will be the length of the longest line in the input.

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PR Comment: https://git.openjdk.org/jdk/pull/25863#issuecomment-2982169343