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

[Сергей Цыпанов]

On Thu, 25 Aug 2022 17:31:05 GMT, Brian Burkhalter <bpb 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
>
> src/java.base/share/classes/java/io/RandomAccessFile.java line 78:
> 
>> 76:     private volatile boolean closed;
>> 77: 
>> 78:     private final byte[] readBuffer = new byte[8];
> 
> As `readBuffer` is used in multiple places without synchronization, doesn't this create a race condition?

It does in case one deliberate accesses the same instance from multiple threads, but there are no thread-safety guarantees for RandomAccessFile. The same shared buffer approach is used in `DataInputStream` so I think we can use it here as well.

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