Rid pointless wrapping with BufferedInputStream from class reading

[stsypanov]

Current implementation of SimpleMetadataReader.getClassReader() wraps InputStream of argument resource with BufferedInputStream which is pointless. Rationale:

• bufferisation anyway happens in ClassReader.readStream()
• buffer sizes are different in BufferedInputStream and in ClassReader.readStream(): 8192 vs 4096 which means that ClassReader.readStream() has to do two calls to read full buffer of BufferedInputStream
• most of the InputStreams returned from JDK classes are already wrapped into BufferedInputStream, e.g. FileURLConnection.getInputStream() or built around ByteBuffer

I've used the benchmark to measure impact of this change:

@State(org.openjdk.jmh.annotations.Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g", "-XX:+UseParallelGC"})
public class MetadataReaderBenchmark {
  private final MetadataReaderFactory metadataReaderFactory = new SimpleMetadataReaderFactory();

  @Benchmark
  public Object read() throws IOException {
    return metadataReaderFactory.getMetadataReader(AnnotatedComponent.class.getName()).getAnnotationMetadata();
  }

  @Component("myName")
  @Scope(BeanDefinition.SCOPE_PROTOTYPE)
  private static class AnnotatedComponent implements Serializable {
    private final Dependency dep;

    @Autowired
    public AnnotatedComponent(@Qualifier("myColor") Dependency dep) {
      this.dep = dep;
    }

    private static class Dependency {
    }
  }
}

For JDK 8 and 11 it gives

JDK 8

original
                                       Mode  Cnt      Score     Error   Units
read                                   avgt  100    122.041 ±   1.286   us/op
read:·gc.alloc.rate                    avgt  100    264.757 ±   2.681  MB/sec
read:·gc.alloc.rate.norm               avgt  100  50795.798 ±  13.941    B/op  <<
read:·gc.churn.PS_Eden_Space           avgt  100    265.543 ±   5.381  MB/sec
read:·gc.churn.PS_Eden_Space.norm      avgt  100  50958.660 ± 976.843    B/op
read:·gc.churn.PS_Survivor_Space       avgt  100      0.191 ±   0.029  MB/sec
read:·gc.churn.PS_Survivor_Space.norm  avgt  100     36.690 ±   5.533    B/op
read:·gc.count                         avgt  100    787.000            counts
read:·gc.time                          avgt  100    873.000                ms

patched
                                       Mode  Cnt      Score     Error   Units
read                                   avgt  100    119.524 ±   1.171   us/op
read:·gc.alloc.rate                    avgt  100    226.871 ±   2.189  MB/sec
read:·gc.alloc.rate.norm               avgt  100  42635.578 ±  10.866    B/op <<
read:·gc.churn.PS_Eden_Space           avgt  100    227.270 ±   5.083  MB/sec
read:·gc.churn.PS_Eden_Space.norm      avgt  100  42708.409 ± 852.571    B/op
read:·gc.churn.PS_Survivor_Space       avgt  100      0.197 ±   0.028  MB/sec
read:·gc.churn.PS_Survivor_Space.norm  avgt  100     37.063 ±   5.137    B/op
read:·gc.count                         avgt  100    832.000            counts
read:·gc.time                          avgt  100    911.000                ms

JDK 11

original
                                       Mode  Cnt      Score      Error   Units
read                                   avgt  100    114.142 ±    3.338   us/op
read:·gc.alloc.rate                    avgt  100    183.482 ±    4.465  MB/sec
read:·gc.alloc.rate.norm               avgt  100  32761.715 ±   29.115    B/op  <<
read:·gc.churn.G1_Eden_Space           avgt  100    183.591 ±   12.077  MB/sec
read:·gc.churn.G1_Eden_Space.norm      avgt  100  32828.788 ± 2166.483    B/op
read:·gc.churn.G1_Old_Gen              avgt  100      0.002 ±    0.001  MB/sec
read:·gc.churn.G1_Old_Gen.norm         avgt  100      0.411 ±    0.196    B/op
read:·gc.count                         avgt  100    185.000             counts
read:·gc.time                          avgt  100     87.000                 ms


patched
                                       Mode  Cnt      Score      Error   Units
read                                   avgt  100    108.903 ±    1.281   us/op
read:·gc.alloc.rate                    avgt  100    144.005 ±    1.686  MB/sec
read:·gc.alloc.rate.norm               avgt  100  24652.976 ±   32.380    B/op  <<
read:·gc.churn.G1_Eden_Space           avgt  100    144.694 ±   16.832  MB/sec
read:·gc.churn.G1_Eden_Space.norm      avgt  100  24744.527 ± 2840.441    B/op
read:·gc.churn.G1_Old_Gen              avgt  100      0.003 ±    0.004  MB/sec
read:·gc.churn.G1_Old_Gen.norm         avgt  100      0.533 ±    0.701    B/op
read:·gc.churn.G1_Survivor_Space       avgt  100      0.133 ±    0.136  MB/sec
read:·gc.churn.G1_Survivor_Space.norm  avgt  100     22.722 ±   23.243    B/op
read:·gc.count                         avgt  100    146.000             counts
read:·gc.time                          avgt  100    118.000                 ms

While execution time is only slightly better, memory consumption is 16-24% lower.