RFR: 8292937: Improve performance of some read operations of RandomAccessFile

[Сергей Цыпанов]

On Fri, 26 Aug 2022 01:49:06 GMT, Quan Anh Mai <duke at openjdk.org> wrote:

>>> Maybe you can modify the read0 method to receive a width parameter additionally.
>> 
>> @merykitty sorry, I don't get it. We already have `readBytes0()` returning array. Why do we need to add a new param to `read0`?
>
> @stsypanov `readBytes0` reads an arbitrary number of bytes and writes them to the given buffer. What I mean here is to have `read0` read 1, 2, 4 or 8 bytes then extend the result to a `jlong`, remove the need to write the result in an array.

@merykitty Done. The new results are:

Benchmark                                (kiloBytes)  Mode  Cnt     Score    Error  Units
RandomAccessFileReadBenchmark.readInt              1  avgt   60   340,514 ± 11,205  us/op
RandomAccessFileReadBenchmark.readInt              5  avgt   60  1244,474 ± 40,376  us/op
RandomAccessFileReadBenchmark.readLong             1  avgt   60   237,004 ± 13,055  us/op
RandomAccessFileReadBenchmark.readLong             5  avgt   60   641,820 ±  4,896  us/op
RandomAccessFileReadBenchmark.readShort            1  avgt   60   542,874 ±  3,304  us/op
RandomAccessFileReadBenchmark.readShort            5  avgt   60  2166,878 ± 30,491  us/op

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PR: https://git.openjdk.org/jdk/pull/10031