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8291598: Matcher.appendReplacement should not create new StringBuilder instances #13048

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@rgiulietti rgiulietti commented Mar 15, 2023

Remove instantiation of StringBuilder


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  • JDK-8291598: Matcher.appendReplacement should not create new StringBuilder instances

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bridgekeeper bot commented Mar 15, 2023

👋 Welcome back rgiulietti! 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 openjdk bot added the rfr Pull request is ready for review label Mar 15, 2023
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@rgiulietti The following label will be automatically applied to this pull request:

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@openjdk openjdk bot added the core-libs core-libs-dev@openjdk.org label Mar 15, 2023
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Benchmark for the example in the documentation for Matcher.appendReplacement()

before

Benchmark                                Mode  Cnt    Score   Error  Units
AppendReplacement.testAppendReplacement  avgt   15  177.029 ± 6.294  ns/op

after

Benchmark                                Mode  Cnt    Score   Error  Units
AppendReplacement.testAppendReplacement  avgt   15  142.373 ± 1.684  ns/op

Same example, but with pattern "(cat)" (1 capturing group), matcher on the input repeated 1000 times, and replacement string "$1dog$1cat$1mouse" (3 back references).

before

Benchmark                                Mode  Cnt       Score      Error  Units
AppendReplacement.testAppendReplacement  avgt   15  262576.335 ± 3718.905  ns/op

after

Benchmark                                Mode  Cnt       Score     Error  Units
AppendReplacement.testAppendReplacement  avgt   15  225700.642 ± 683.721  ns/op

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mlbridge bot commented Mar 15, 2023

Webrevs

Comment on lines 1056 to 1066
StringBuilder gsb = new StringBuilder();
while (cursor < replacement.length()) {
nextChar = replacement.charAt(cursor);
if (ASCII.isLower(nextChar) ||
ASCII.isUpper(nextChar) ||
ASCII.isDigit(nextChar)) {
gsb.append(nextChar);
cursor++;
} else {
break;
}
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Possibly remove another SB allocation; remember start and end and use replacement.substring(start, end).

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Thanks @RogerRiggs, addressed in latest commit.

…r instances

Removed other allocations of StringBuilder when processing named groups in replacement string.
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Waiting for other comments and review

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Sorry for the delay.
The workaround for appending to StringBuffer/StringBuilder is awkward, adding a try/catch that can't happen. But I don't have a better suggestion.
It is scoped to the appendExpandedReplacement method and has no runtime impact.

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openjdk bot commented Mar 28, 2023

@rgiulietti 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:

8291598: Matcher.appendReplacement should not create new StringBuilder instances

Reviewed-by: rriggs

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@openjdk openjdk bot added the ready Pull request is ready to be integrated label Mar 28, 2023
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@RogerRiggs Yes, it would be nice to be able to write

private void appendExpandedReplacement(StringBuilder | StringBuffer app, String replacement) 

and get rid of the try statement altogether.

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/integrate

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openjdk bot commented Mar 28, 2023

Going to push as commit ca745cb.
Since your change was applied there have been 157 commits pushed to the master branch:

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Mar 28, 2023
@openjdk openjdk bot closed this Mar 28, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Mar 28, 2023
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@rgiulietti Pushed as commit ca745cb.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

@rgiulietti rgiulietti deleted the JDK-8291598 branch March 29, 2023 12:46
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