Re: RFR: 8325730: StringBuilder.toString allocation for the empty String [v2]
On Tue, 20 Feb 2024 18:04:18 GMT, Claes Redestad wrote:
>> src/java.base/share/classes/java/lang/StringBuilder.java line 478:
>>
>>> 476: }
>>> 477: // Create a copy, don't share the array
>>> 478: return new String(this, null);
>>
>> Ok, this got me a bit confused, but I think this just inlines the call to
>> this constructor:
>>
>>
>> public String(StringBuilder builder) {
>> this(builder, null);
>> }
>
> Yes, I was mostly reaching for increased consistency with `StringBuffer` here.
Good then, thanks.
>> test/micro/org/openjdk/bench/java/lang/StringBuilderToString.java line 33:
>>
>>> 31: import org.openjdk.jmh.annotations.Param;
>>> 32: import org.openjdk.jmh.annotations.Scope;
>>> 33: import org.openjdk.jmh.annotations.Setup;
>>
>> Is this needed?
>
> It's needed again now that I reverted the code removals.. :-)
Mhm. I don't see any new `@Setup` methods anywhere. Just checked out the PR
locally, removed this import and benchmarks still build, and
`StringBuilderToString` bench still runs. Am I missing something here?
-
PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496297773
PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496315384
Re: RFR: 8325730: StringBuilder.toString allocation for the empty String [v2]
On Tue, 20 Feb 2024 18:08:11 GMT, Aleksey Shipilev wrote: >> I couldn't figure out why we'd want to have `String::substring` micros in a >> test `StringBuffers` (there's also a `StringSubstring` micro), though I >> could deal with that as an explicit cleanup RFE. > > Yeah, I would like to keep this change clean for backports. Do the cleanup in > a separate PR? Reverted. - PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496281834
Re: RFR: 8325730: StringBuilder.toString allocation for the empty String [v2]
On Tue, 20 Feb 2024 18:00:42 GMT, Claes Redestad wrote:
>> test/micro/org/openjdk/bench/java/lang/StringBuffers.java line 49:
>>
>>> 47:
>>> 48: @Benchmark
>>> 49: public String emptyToString() {
>>
>> Do we actually need to remove the `substring` test here?
>
> I couldn't figure out why we'd want to have `String::substring` micros in a
> test `StringBuffers` (there's also a `StringSubstring` micro), though I could
> deal with that as an explicit cleanup RFE.
Yeah, I would like to keep this change clean for backports. Do the cleanup in a
separate PR?
-
PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496277852
Re: RFR: 8325730: StringBuilder.toString allocation for the empty String [v2]
On Tue, 20 Feb 2024 17:02:40 GMT, Aleksey Shipilev wrote:
>> Claes Redestad has updated the pull request incrementally with two
>> additional commits since the last revision:
>>
>> - Revert StringBuffers removals
>> - Update from review comments by @shipilev
>
> src/java.base/share/classes/java/lang/StringBuilder.java line 478:
>
>> 476: }
>> 477: // Create a copy, don't share the array
>> 478: return new String(this, null);
>
> Ok, this got me a bit confused, but I think this just inlines the call to
> this constructor:
>
>
> public String(StringBuilder builder) {
> this(builder, null);
> }
Yes, I was mostly reaching for increased consistency with `StringBuffer` here.
> test/micro/org/openjdk/bench/java/lang/StringBuilderToString.java line 33:
>
>> 31: import org.openjdk.jmh.annotations.Param;
>> 32: import org.openjdk.jmh.annotations.Scope;
>> 33: import org.openjdk.jmh.annotations.Setup;
>
> Is this needed?
It's needed again now that I reverted the code removals.. :-)
> test/micro/org/openjdk/bench/java/lang/StringBuilders.java line 407:
>
>> 405:
>> 406: private void generateData() {
>> 407: sb = new StringBuilder(length);
>
> This looks weird, given there is a `sb` initialization two lines below. Is
> this `sbEmpty`, really?
Yes, updating the name to avoid the confusing shadowing.
-
PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496273112
PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496282094
PR Review Comment: https://git.openjdk.org/jdk/pull/17931#discussion_r1496275704
Re: RFR: 8325730: StringBuilder.toString allocation for the empty String [v2]
> JDK-8282429 accidentally removed an optimization (JDK-8240094) that ensured > StringBuilder/StringBuffer::toString returns `""` when the builders are empty. > > > Name Cnt Base Error Test Error Unit > Change > StringBuffers.emptyToString5 12,289 ±0,384 9,883 ± 0,721 ns/op > 1,24x (p = 0,000*) > :gc.alloc.rate 1862,398 ± 57,647 0,007 ± 0,000 MB/sec > 0,00x (p = 0,000*) > :gc.alloc.rate.norm 24,000 ±0,000 0,000 ± 0,000 B/op > 0,00x (p = 0,000*) > :gc.count31,000 0,000 counts > :gc.time 21,000 ms > StringBuilders.emptyToString 54,146 ±0,567 0,646 ± 0,003 ns/op > 6,42x (p = 0,000*) > :gc.alloc.rate 9208,656 ± 1234,399 0,007 ± 0,000 MB/sec > 0,00x (p = 0,000*) > :gc.alloc.rate.norm 40,000 ±0,000 0,000 ± 0,000 B/op > 0,00x (p = 0,000*) > :gc.count96,000 0,000 counts > :gc.time 64,000 ms > * = significant Claes Redestad has updated the pull request incrementally with two additional commits since the last revision: - Revert StringBuffers removals - Update from review comments by @shipilev - Changes: - all: https://git.openjdk.org/jdk/pull/17931/files - new: https://git.openjdk.org/jdk/pull/17931/files/7f9566b8..40cca3e3 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=17931&range=01 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17931&range=00-01 Stats: 41 lines in 2 files changed: 38 ins; 0 del; 3 mod Patch: https://git.openjdk.org/jdk/pull/17931.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/17931/head:pull/17931 PR: https://git.openjdk.org/jdk/pull/17931
