Improve performance and avoid memory consumption if logging primitive arrays as parameters

[magicwerk]

It is one of the design goals of Log4j "to deliver excelling performance without almost any burden on the Java garbage collector."

However this is currently not true for primitive arrays, here Log4j allocates unneeded temporary strings if a primitive array is logged as parameter.

Current implementation:
Method ParameterFormatter.appendArray() delegats to java.util.Arrays.toString() which then allocates a new StringBuilder to return a String which is then added to the existing StringBuilder.

Improved implementation:
For all primitive types, a method like ParameterFormatter.appendArray(int[], StringBuilder) has been added which is called by ParameterFormatter.appendArray() and avoids the unnecessary object creation.

A JHM benchmark shows that this changes increases performance and reduces memory consumption to zero:

Benchmark Mode Cnt Score Error Units testParameterFormatterNew thrpt 5 10090997.276 � 758239.856 ops/s testParameterFormatterNew:gc.alloc.rate thrpt 5 0.001 � 0.001 MB/sec testParameterFormatterNew:gc.alloc.rate.norm thrpt 5 ? 10?? B/op testParameterFormatterNew:gc.count thrpt 5 ? 0 counts testParameterFormatterOld thrpt 5 8259447.275 � 349015.042 ops/s testParameterFormatterOld:gc.alloc.rate thrpt 5 1259.364 � 54.827 MB/sec testParameterFormatterOld:gc.alloc.rate.norm thrpt 5 160.000 � 0.001 B/op testParameterFormatterOld:gc.count thrpt 5 11.000 counts testParameterFormatterOld:gc.time thrpt 5 11.000 ms 

Tests have been added to ParameterFormatterTest

[github-actions]

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-macos-latest	clean install	3.9.8	✅
build-ubuntu-latest	clean install	3.9.8	✅
build-windows-latest	clean install	3.9.8	✅

Generated by gradle/develocity-actions

[ppkarwasz]

@magicwerk,

Looks good to me.

Can you also add a benchmark to ParameterFormatterBenchmark for the old and new version? Due to scalar inlining, str.append(Arrays.toString((int[]) o)) might actually also become GC-free on some JVMs.

[ppkarwasz]

@magicwerk,

All commits in this PR must have verified signatures, so you need to:

• Add a GPG key to your GitHub account.
• Rebase your branch to resign the commits:

  git rebase --force-rebase --gpg-sign origin/2.x git push --force

[magicwerk]

I doubt that any JVM could optimize away the Arrays.toString() call, I have only seen more or less constants strings go.
Nevertheless I have added benchmarks to ParameterFormatterBenchmark.
I was not quite sure how you would like to implement old vs new as the old implementation is obviously gone, have a look.
I had to copy the source of a single appendArray() method as they are private and cannot be accessed.

Benchmark Mode Cnt Score Error Units ParameterFormatterBenchmark.appendArrayStringBuilder sample 1030560 173.057 ± 5.219 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.00 sample ? 0 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.50 sample 100.000 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.90 sample 200.000 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.95 sample 300.000 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.99 sample 300.000 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.999 sample 1100.000 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p0.9999 sample 78008.192 ns/op ParameterFormatterBenchmark.appendArrayStringBuilder:p1.00 sample 377856.000 ns/op ParameterFormatterBenchmark.appendArrayToString sample 920507 192.249 ± 9.528 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.00 sample ? 0 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.50 sample 200.000 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.90 sample 200.000 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.95 sample 300.000 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.99 sample 300.000 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.999 sample 3600.000 ns/op ParameterFormatterBenchmark.appendArrayToString:p0.9999 sample 75333.478 ns/op ParameterFormatterBenchmark.appendArrayToString:p1.00 sample 1880064.000 ns/op 

[magicwerk]

I tried to sign the commits by executing your command - is it ok now?

About resolving conversion: am I doing that if I have replied or you if you think my reply was ok?

[ppkarwasz]

@magicwerk,

Looks almost good to go, thanks!

One last thing: can you add a changelog entry in src/changelog/.2.x.x/. Look at the other entries for inspiration.

The change type for performance improvements are either fixed or changed.

[ppkarwasz]

@magicwerk,

Thanks, I'll merge it as soon as the required tests pass.