On Sun, 21 Aug 2022 20:07:10 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
>
> Сергей Цыпанов has updated the pull request incrementally with one additional
> commit since the last revision:
>
> 8292698: Fix copyright year
Btw, I've tried to reimplement `readInt()` in a way similar to `readLong()`:
public final int readInt() throws IOException {
readFully(readBuffer, 0, 4);
return (readBuffer[0] & 0xff) << 24
+ (readBuffer[1] & 0xff) << 16
+ (readBuffer[2] & 0xff) << 8
+ (readBuffer[3] & 0xff);
}
but with this change the build fails with
Building target 'test' in configuration 'macosx-x86_64-server-release'
Compiling 3158 files for java.base
Updating support/src.zip
Optimizing the exploded image
Error occurred during initialization of boot layer
java.lang.module.FindException: Error reading module:
/Users/stsypanov/IdeaProjects/jdk/build/macosx-x86_64-server-release/jdk/modules/java.management.rmi
Caused by: java.lang.module.InvalidModuleDescriptorException: Bad magic number
make[3]: ***
[/Users/stsypanov/IdeaProjects/jdk/build/macosx-x86_64-server-release/jdk/_optimize_image_exec.marker]
Error 1
make[2]: *** [exploded-image-optimize] Error 2
ERROR: Build failed for target 'test' in configuration
'macosx-x86_64-server-release' (exit code 2)
Stopping sjavac server
=== Output from failing command(s) repeated here ===
* For target jdk__optimize_image_exec:
Error occurred during initialization of boot layer
java.lang.module.FindException: Error reading module:
/Users/stsypanov/IdeaProjects/jdk/build/macosx-x86_64-server-release/jdk/modules/java.management.rmi
Caused by: java.lang.module.InvalidModuleDescriptorException: Bad magic number
* All command lines available in
/Users/stsypanov/IdeaProjects/jdk/build/macosx-x86_64-server-release/make-support/failure-logs.
=== End of repeated output ===
What is wrong with the change?
-------------
PR: https://git.openjdk.org/jdk/pull/9956
