asmhatreandClaude Sonnet 5.5
fc05eed4b5
Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01KqJyCidz3ZgRyHABv2GVJh
25 lines
2.1 KiB
Markdown
25 lines
2.1 KiB
Markdown
# compact-strings — Compact Strings (JEP 254) measured with JOL, plus compact object headers
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Companion code for the ankurm.com article **Compact Strings in Java: Measured with JOL on JDK 25 (plus Compact Object Headers)**. The explanation lives in the
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article, in collapsible sections; this folder holds the runnable sources and the transcripts they produced.
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```bash
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JDK25=/path/to/jdk-25 JDK27=/path/to/jdk-27 ./run.sh # regenerates output/01-21 (about 40 seconds; downloads JOL 0.17 and checks its sha1)
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./jmh/fetch.sh && JDK25=/path/to/jdk-25 ./jmh/run-jmh.sh # output/30-jmh.txt (about 6 minutes; machine dependent)
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```
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- `src/StringLayout.java` — JOL `ClassLayout` of `String`, of a Latin-1 and a UTF-16 instance and of the `byte[]` behind each; a footprint table by length. Needs `--add-opens java.base/java.lang=ALL-UNNAMED` to read `coder`.
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- `src/MillionStrings.java` — one million random lower-case strings (30 to 55 characters), measured with `GraphLayout`, then the same strings with one `€` appended.
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- `src/Upgrade.java` — the `coder` of strings produced by concatenation, `substring`, `replace`, `toLowerCase`, `new String(bytes, UTF_8)`, `StringBuilder.toString()`.
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- `jmh/` — a JMH 1.37 benchmark of six read-only `String` operations with and without `-XX:-CompactStrings`.
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- `output/` — `01`-`06` layouts, `11`-`16` the million-string runs, each under six flag sets (JDK 25 default, `-XX:-CompactStrings`, `-XX:+UseCompactObjectHeaders`, both; JDK 27 default and `-XX:-UseCompactObjectHeaders`), `20` coder transcript, `21` `PrintFlagsFinal`, `30` JMH.
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| Thing | Version |
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|---|---|
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| JDK 25 | Temurin 25.0.4.1+1 |
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| JDK 27 | Amazon Corretto 27+35 (`corretto.aws/downloads/latest/amazon-corretto-27-x64-linux-jdk.tar.gz`) |
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| JOL | 0.17 (`org.openjdk.jol:jol-core`, latest release in Maven Central's `maven-metadata.xml`) |
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| JMH | 1.37 |
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Everything except the JMH numbers is byte-stable. JOL 0.17 on JDK 27 prints one `Unable to attach Serviceability Agent` line (it reads a flag that no longer exists); it is kept in the transcripts because it is real.
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