On Sun, 21 Aug 2022 06:29:43 GMT, Сергей Цыпанов <d...@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
I've revert dubious changes
-------------
PR: https://git.openjdk.org/jdk/pull/9956
