Hello, from discussion in https://github.com/openjdk/jdk/pull/3464 I've found
out, that in a few of JDK core classes, e.g. in `j.l.Class` expressions like
`baseName.replace('.', '/') + '/' + name` are not compiled into
`invokedynamic`-based code, but into one using `StringBuilder`. This happens
due to some bootstraping issues.
However the code like
private String getSimpleName0() {
if (isArray()) {
return getComponentType().getSimpleName() + "[]";
}
//...
}
can be improved via replacement of `+` with `String.concat()` call.
I've used this benchmark to measure impact:
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class ClassMethodsBenchmark {
private final Class<? extends Object[]> arrayClass = Object[].class;
private Method descriptorString;
@Setup
public void setUp() throws NoSuchMethodException {
//fore some reason compiler doesn't allow me to call
Class.descriptorString() directly
descriptorString = Class.class.getDeclaredMethod("descriptorString");
}
@Benchmark
public Object descriptorString() throws Exception {
return descriptorString.invoke(arrayClass);
}
@Benchmark
public Object typeName() {
return arrayClass.getTypeName();
}
}
and got those results
Mode Cnt Score
Error Units
descriptorString avgt 60 91.480 ±
1.839 ns/op
descriptorString:·gc.alloc.rate.norm avgt 60 404.008 ±
4.033 B/op
descriptorString:·gc.churn.G1_Eden_Space avgt 60 2791.866 ±
181.589 MB/sec
descriptorString:·gc.churn.G1_Eden_Space.norm avgt 60 401.702 ±
26.047 B/op
descriptorString:·gc.churn.G1_Survivor_Space avgt 60 0.003 ±
0.001 MB/sec
descriptorString:·gc.churn.G1_Survivor_Space.norm avgt 60 ≈ 10⁻³
B/op
descriptorString:·gc.count avgt 60 205.000
counts
descriptorString:·gc.time avgt 60 216.000
ms
patched
Mode Cnt Score
Error Units
descriptorString avgt 60 65.016 ±
3.446 ns/op
descriptorString:·gc.alloc.rate avgt 60 2844.240 ±
115.719 MB/sec
descriptorString:·gc.alloc.rate.norm avgt 60 288.006 ±
0.001 B/op
descriptorString:·gc.churn.G1_Eden_Space avgt 60 2832.996 ±
206.939 MB/sec
descriptorString:·gc.churn.G1_Eden_Space.norm avgt 60 286.955 ±
17.853 B/op
descriptorString:·gc.churn.G1_Survivor_Space avgt 60 0.003 ±
0.001 MB/sec
descriptorString:·gc.churn.G1_Survivor_Space.norm avgt 60 ≈ 10⁻³
B/op
descriptorString:·gc.count avgt 60 208.000
counts
descriptorString:·gc.time avgt 60 228.000
ms
-----------------
typeName avgt 60 34.273 ±
0.480 ns/op
typeName:·gc.alloc.rate avgt 60 3265.356 ±
45.113 MB/sec
typeName:·gc.alloc.rate.norm avgt 60 176.004 ±
0.001 B/op
typeName:·gc.churn.G1_Eden_Space avgt 60 3268.454 ±
134.458 MB/sec
typeName:·gc.churn.G1_Eden_Space.norm avgt 60 176.109 ±
6.595 B/op
typeName:·gc.churn.G1_Survivor_Space avgt 60 0.003 ±
0.001 MB/sec
typeName:·gc.churn.G1_Survivor_Space.norm avgt 60 ≈ 10⁻⁴
B/op
typeName:·gc.count avgt 60 240.000
counts
typeName:·gc.time avgt 60 255.000
ms
patched
typeName avgt 60 15.787 ±
0.214 ns/op
typeName:·gc.alloc.rate avgt 60 2577.554 ±
32.339 MB/sec
typeName:·gc.alloc.rate.norm avgt 60 64.001 ±
0.001 B/op
typeName:·gc.churn.G1_Eden_Space avgt 60 2574.039 ±
147.774 MB/sec
typeName:·gc.churn.G1_Eden_Space.norm avgt 60 63.895 ±
3.511 B/op
typeName:·gc.churn.G1_Survivor_Space avgt 60 0.003 ±
0.001 MB/sec
typeName:·gc.churn.G1_Survivor_Space.norm avgt 60 ≈ 10⁻⁴
B/op
typeName:·gc.count avgt 60 189.000
counts
typeName:·gc.time avgt 60 199.000
ms
I think this patch is likely to improve reflection operations related to arrays.
If one finds this patch useful, then I'll create a ticket to track this. Also
it'd be nice to have a list of classes, that are compiled in the same way as
`j.l.Class` (i.e. have no access to `invokedynamic`) so I could look into them
for other snippets where two String are joined so `concat`-based optimization
is possible.
Pre-sizing of `StringBuilder` for `Class.gdescriptorString()` and
`Class.getCanonicalName0()` is one more improvement opportunity here.
-------------
Commit messages:
- Use String.concat() where invokedynamic-based String concatenation is not
available
Changes: https://git.openjdk.java.net/jdk/pull/3627/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3627&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8266972
Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
Patch: https://git.openjdk.java.net/jdk/pull/3627.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/3627/head:pull/3627
PR: https://git.openjdk.java.net/jdk/pull/3627
