RFR: 8255299: Drop explicit zeroing at instantiation of Atomic* objects
Сергей Цыпанов
github.com+10835776+stsypanov at openjdk.java.net
Fri Oct 23 08:03:51 UTC 2020
As discussed in https://github.com/openjdk/jdk/pull/510 there is never a reason to explicitly instantiate any instance of `Atomic*` class with its default value, i.e. `new AtomicInteger(0)` could be replaced with `new AtomicInteger()` which is faster:
@State(Scope.Thread)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@BenchmarkMode(value = Mode.AverageTime)
public class AtomicBenchmark {
@Benchmark
public Object defaultValue() {
return new AtomicInteger();
}
@Benchmark
public Object explicitValue() {
return new AtomicInteger(0);
}
}
THis benchmark demonstrates that `explicitValue()` is much slower:
Benchmark Mode Cnt Score Error Units
AtomicBenchmark.defaultValue avgt 30 4.778 ± 0.403 ns/op
AtomicBenchmark.explicitValue avgt 30 11.846 ± 0.273 ns/op
So meanwhile https://bugs.openjdk.java.net/browse/JDK-8145948 is still in progress we could trivially replace explicit zeroing with default constructors gaining some performance benefit with no risk.
I've tested the changes locally, both tier1 and tier 2 are ok.
Could one create an issue for tracking this?
-------------
Commit messages:
- 8255299: Drop explicit zeroing at instantiation of Atomic* objects
Changes: https://git.openjdk.java.net/jdk/pull/818/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=818&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8255299
Stats: 19 lines in 17 files changed: 0 ins; 3 del; 16 mod
Patch: https://git.openjdk.java.net/jdk/pull/818.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/818/head:pull/818
PR: https://git.openjdk.java.net/jdk/pull/818
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