8255299: Drop explicit zeroing at instantiation of Atomic* objects

[stsypanov]

As discussed in #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?

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Testing

	Linux x64	Linux x86	Windows x64	macOS x64
Build	✔️ (5/5 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)
Test (tier1)	✔️ (9/9 passed)	✔️ (9/9 passed)	✔️ (9/9 passed)	✔️ (9/9 passed)

Issue

• JDK-8255299: Drop explicit zeroing at instantiation of Atomic* objects

Reviewers

• Claes Redestad (@cl4es - Reviewer) ⚠️ Review applies to c1fb362f6d2f4c099c05ef606daf881ebde475de
• Sergey Bylokhov (@mrserb - Reviewer) ⚠️ Review applies to c1fb362f6d2f4c099c05ef606daf881ebde475de
• Phil Race (@prrace - Reviewer) ⚠️ Review applies to c1fb362f6d2f4c099c05ef606daf881ebde475de

Download

$ git fetch https://git.openjdk.java.net/jdk pull/818/head:pull/818
$ git checkout pull/818

[bridgekeeper]

👋 Welcome back stsypanov! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@stsypanov The following labels will be automatically applied to this pull request:

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[cl4es]

Filed 8255299 for this. Prefix the name of the PR with "8255299: " and it should pass checks.

[mlbridge]

Webrevs

• 01: Full - Incremental (7dc646d)
• 00: Full (c1fb362f6d2f4c099c05ef606daf881ebde475de)

[openjdk]

⚠️ @stsypanov the full name on your profile does not match the author name in this pull requests' HEAD commit. If this pull request gets integrated then the author name from this pull requests' HEAD commit will be used for the resulting commit. If you wish to push a new commit with a different author name, then please run the following commands in a local repository of your personal fork:

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[openjdk]

@stsypanov This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8255299: Drop explicit zeroing at instantiation of Atomic* objects

Reviewed-by: redestad, serb, prr

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 4 new commits pushed to the master branch:

• 591e7e2: 8255378: [Vector API] Remove redundant vector length check after JDK-8254814 and JDK-8255210
• 2c9dfc7: 8255234: ZGC: Bulk allocate forwarding data structures
• b7d483c: 8255245: C1: Fix output of -XX:+PrintCFGToFile to open it with visualizer
• 5e0a8cd: 8255488: Re-enable some problem listed tests

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@cl4es, @mrserb, @prrace) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[mrserb]

The changes in src/java.desktop looks fine.

[stsypanov]

/integrate

[openjdk]

@stsypanov
Your change (at version c1fb362f6d2f4c099c05ef606daf881ebde475de) is now ready to be sponsored by a Committer.

[dfuch]

Changes to java.logging and java.net.http also look good to me.

[dfuch]

Hi Sergey,

I'll give it some testing and sponsor it next week unless someone else steps up.

best regards,
-- daniel

[prrace]

client changes are fine

[stsypanov]

Rebased onto master to have the fix introduced in #778

[mrserb]

FYI it is better to use merge, instead of rebase+force push. Rebase breaks history and all existed code comments.

[stsypanov]

@mrserb thanks for pointing this out!

[stsypanov]

/integrate

[openjdk]

@stsypanov
Your change (at version 7dc646d) is now ready to be sponsored by a Committer.

[dfuch]

Thanks for updating with latest master changes Sergey! My tests were all green.
/sponsor

[openjdk]

@dfuch @stsypanov Since your change was applied there have been 5 commits pushed to the master branch:

• 6b2d11b: 8255246: AArch64: Implement BigInteger shiftRight and shiftLeft accelerator/intrinsic
• 591e7e2: 8255378: [Vector API] Remove redundant vector length check after JDK-8254814 and JDK-8255210
• 2c9dfc7: 8255234: ZGC: Bulk allocate forwarding data structures
• b7d483c: 8255245: C1: Fix output of -XX:+PrintCFGToFile to open it with visualizer
• 5e0a8cd: 8255488: Re-enable some problem listed tests

Your commit was automatically rebased without conflicts.

Pushed as commit 3c4fc79.

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