Integrated: 8292698: Improve performance of DataInputStream

[Сергей Цыпанов]

On Sun, 21 Aug 2022 06:29:43 GMT, Сергей Цыпанов <duke at openjdk.org> wrote:

> I found out that reading from `DataInputStream` wrapping `ByteArrayInputStream` (as well as `BufferedInputStream` or any `InputStream` relying on `byte[]`) can be significantly improved by accessing volatile `in` field only once per operation.
> 
> Current implementation does it for each call of `in.read()`, i.e. in `readInt()` method we do it 4 times:
> 
> public final int readInt() throws IOException {
>     int ch1 = in.read();
>     int ch2 = in.read();
>     int ch3 = in.read();
>     int ch4 = in.read();
>     if ((ch1 | ch2 | ch3 | ch4) < 0)
>         throw new EOFException();
>     return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
> }
> 
> Apparently accessing volatile reference with underlying `byte[]` prevents runtime from doing some optimizations, so dereferencing local variable should be more efficient.
> 
> Benchmarking:
> 
> baseline:
> 
> Benchmark                     Mode  Cnt   Score   Error  Units
> DataInputStreamTest.readChar  avgt   20  22,889 ± 0,648  us/op
> DataInputStreamTest.readInt   avgt   20  21,804 ± 0,197  us/op
> 
> patch:
> 
> Benchmark                     Mode  Cnt   Score   Error  Units
> DataInputStreamTest.readChar  avgt   20  11,018 ± 0,089  us/op
> DataInputStreamTest.readInt   avgt   20   5,608 ± 0,087  us/op

This pull request has now been integrated.

Changeset: 74a51ccc
Author:    Sergey Tsypanov <sergei.tsypanov at yandex.ru>
Committer: Jaikiran Pai <jpai at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/74a51ccc86525eb4b1eb2e5cb11e605ca9e9fc5d
Stats:     98 lines in 2 files changed: 71 ins; 14 del; 13 mod

8292698: Improve performance of DataInputStream

Reviewed-by: dfuchs

-------------

PR: https://git.openjdk.org/jdk/pull/9956