RFR: 8291641: Optimize StackTraceElement.toString() [v3]

[Quan Anh Mai]

On Tue, 2 Aug 2022 13:34:26 GMT, David Schlosnagle <duke at openjdk.org> wrote:

>> I would like to contribute an optimized version of `StackTraceElement#toString()` that uses a single StringBuilder throughout creation to avoid intermediate `String` allocations. `StackTraceElement#toString()` is used in a number of JDK code paths including `Throwable#printStackTrace()`, as well as many JDK consumers may transform `StackTraceElement` `toString()` in logging frameworks capturing throwables and exceptions, and diagnostics performing dumps.
>> 
>> Given this usage and some observed JFR profiles from production services, I'd like to reduce the intermediate allocations to reduce CPU pressure in these circumstances. I have added a couple benchmarks for a sample `Throwable#printStackTrace()` converted to String via `StringWriter` and individual `StackTraceElement` `toString`. The former shows ~15% improvement, while the latter shows ~40% improvement.
>> 
>> Before
>> 
>> Benchmark                               Mode  Cnt       Score      Error  Units
>> StackTraceElementBench.printStackTrace  avgt   15  167147.066 ± 4260.521  ns/op
>> StackTraceElementBench.toString         avgt   15     132.781 ±    2.095  ns/op
>> 
>> 
>> After
>> 
>> Benchmark                               Mode  Cnt       Score      Error  Units
>> StackTraceElementBench.printStackTrace  avgt   15  142909.133 ± 2290.720  ns/op
>> StackTraceElementBench.toString         avgt   15      78.939 ±    0.469  ns/op
>
> David Schlosnagle has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Estimate length

Otherwise looks good to me, thanks

src/java.base/share/classes/java/lang/StackTraceElement.java line 365:

> 363:                 + methodName.length() + 1
> 364:                 + Math.max("Unknown Source".length(), Objects.requireNonNullElse(fileName, "").length()) + 1
> 365:                 + Integer.stringSize(lineNumber) + 1;

`Integer.stringSize(lineNumber)` can be further simplify to `11`

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PR: https://git.openjdk.org/jdk/pull/9665