RFR: 4926314: Optimize Reader.read(CharBuffer) [v9]

[Alan Bateman]

On Sat, 13 Mar 2021 14:28:25 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 with a new target base due to a merge or a rebase. The pull request now contains 15 commits:
> 
>  - Merge master
>  - Fix bug in CharArrayReader and add unit test
>  - Clean up unit tests
>  - Revert off-heap code path
>  - Replace c-style array declarations
>  - Share work buffer between #skip and #read
>  - Update copyright year
>  - Implement review comment
>  - Revert StreamDecoder changes
>  - Implement CharArrayReader#read(CharBuffer)
>  - ... and 5 more: https://git.openjdk.java.net/jdk/compare/d339320e...c4c859e0

src/java.base/share/classes/java/io/Reader.java line 205:

> 203:                 target.put(cbuf, 0, nread);
> 204:         }
> 205:         return nread;

Thanks for bringing this back to just the heap buffer case. This part looks good now.

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