RFR: 4926314: Optimize Reader.read(CharBuffer) [v7]

[Brian Burkhalter]

On Fri, 12 Feb 2021 09:18:10 GMT, Philippe Marschall <github.com+471021+marschall at openjdk.org> wrote:

>> Implement three optimiztations for Reader.read(CharBuffer)
>> 
>> * Add a code path for heap buffers in Reader#read to use the backing array instead of allocating a new one.
>> * Change the code path for direct buffers in Reader#read to limit the intermediate allocation to `TRANSFER_BUFFER_SIZE`.
>> * Implement `InputStreamReader#read(CharBuffer)` and delegate to `StreamDecoder`.
>> * Implement `StreamDecoder#read(CharBuffer)` and avoid buffer allocation.
>
> Philippe Marschall has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Replace c-style array declarations
>  - Share work buffer between #skip and #read

test/jdk/java/io/InputStreamReader/ReadCharBuffer.java line 34:

> 32: import org.testng.annotations.Test;
> 33: 
> 34: import java.io.*;

It's generally better not to use a wild card.

test/jdk/java/io/InputStreamReader/ReadCharBuffer.java line 73:

> 71:         }
> 72: 
> 73:         buffer.clear();

I think `buffer.rewind()` would be more in keeping with the specification verbiage although there will be no practical effect here. Same comment applies below and in the other test `ReadCharBuffer`.

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PR: https://git.openjdk.java.net/jdk/pull/1915