RFR: 8292937: Improve performance of some read operations of RandomAccessFile [v5]

[Alan Bateman]

On Fri, 26 Aug 2022 20:59:57 GMT, Сергей Цыпанов <duke at openjdk.org> wrote:

>> Currently some operations of RandomAccessFile are implemented with multiple read() invocations:
>> 
>> public final int readInt() throws IOException {
>>     int ch1 = this.read();
>>     int ch2 = this.read();
>>     int ch3 = this.read();
>>     int ch4 = this.read();
>>     if ((ch1 | ch2 | ch3 | ch4) < 0)
>>       throw new EOFException();
>>     return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
>> }
>> 
>> This can be improved by using bulk reads:
>> 
>> public final int readInt() throws IOException {
>>   readFully(readBuffer, 0, 4);
>>   return Bits.getInt(readBuffer, 0);
>> }
>> 
>> Benchmarking:
>> 
>> baselile
>> Benchmark                                (kiloBytes)  Mode  Cnt     Score      Error  Units
>> RandomAccessFileReadBenchmark.readInt              1  avgt   10  1060,526 ±   62,036  us/op
>> RandomAccessFileReadBenchmark.readInt              5  avgt   10  5745,671 ± 1374,277  us/op
>> RandomAccessFileReadBenchmark.readLong             1  avgt   10  1399,494 ±  378,072  us/op
>> RandomAccessFileReadBenchmark.readLong             5  avgt   10  4864,425 ±  329,282  us/op
>> RandomAccessFileReadBenchmark.readShort            1  avgt   10  1111,163 ±   70,883  us/op
>> RandomAccessFileReadBenchmark.readShort            5  avgt   10  4933,058 ±  339,273  us/op
>> 
>> patch
>> Benchmark                                (kiloBytes)  Mode  Cnt     Score    Error  Units
>> RandomAccessFileReadBenchmark.readInt              1  avgt   10   311,404 ± 17,337  us/op
>> RandomAccessFileReadBenchmark.readInt              5  avgt   10  1210,381 ± 22,742  us/op
>> RandomAccessFileReadBenchmark.readLong             1  avgt   10   201,726 ±  8,885  us/op
>> RandomAccessFileReadBenchmark.readLong             5  avgt   10   667,117 ±  6,779  us/op
>> RandomAccessFileReadBenchmark.readShort            1  avgt   10   560,259 ± 16,783  us/op
>> RandomAccessFileReadBenchmark.readShort            5  avgt   10  2251,975 ± 54,533  us/op
>
> Сергей Цыпанов has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - 8292937: Fix error C2057
>  - 8292937: Remove unused method

src/java.base/share/native/libjava/io_util.c line 108:

> 106:                 ((*(buf + 6) & 0xFF) << 8) +
> 107:                 ((*(buf + 7) & 0xFF)));
> 108:     }

Doing this in a JNI method is problematic for several reasons and I think we should try to keep the JNI methods as simple/short as possible, ideally map to a single syscall and not do too much if possible. In the medium/long term then many of the native methods in this area will be replaced anyway, maybe by re-implementing RAF/etc. on NIO, maybe by replacing the JNI code with the java.lang.foreign APIs. In addition, I expect there will be another tranche of changes that will significantly change this code for virtual threads to allow the underlying thread be released when doing for file I/O.

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

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