Spring Drop explicit zeroing at instantiation of Atomic* objects

Often fields of atomic types e.g. AtomicInteger are explicitly zeroed at initialization, which is redundant and slower than relying on default values:

@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);
  }
}

Semantically both new AtomicInteger() and new AtomicInteger(0) are the same, but 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

This is related to https://github.com/spring-projects/spring-framework/pull/25261

Comment From: wind57

very interesting. this seems to happen because there is an explicit volatile write, via : AtomicInteger(0).

Comment From: stsypanov

@wind57 yes, I've mentioned a previous PR being about the same: https://github.com/spring-projects/spring-framework/pull/25261

Also see https://bugs.openjdk.java.net/browse/JDK-8145680