We need a String format solution with good performance. String Template was
once expected, but it has been removed. j.u.Formatter is powerful, but its
performance is not good enough.
This PR implements a subset of j.u.Formatter capabilities. The performance is
good enough that it is a fastpath for commonly used functions. When the
supported functions are exceeded, it will fall back to using j.u.Formatter.
The performance of this implementation is good enough, the fastpath has low
detection cost, There is no noticeable performance degradation when falling
back to j.u.Formatter via fastpath.
Below is a comparison of String.format and concat-based and StringBuilder:
* benchmark java code
public class StringFormat {
@Benchmark
public String stringIntFormat() {
return "%s %d".formatted(s, i);
}
@Benchmark
public String stringIntConcat() {
return s + " " + i;
}
@Benchmark
public String stringIntStringBuilder() {
return new StringBuilder(s).append(" ").append(i).toString();
}
}
* benchmark number on macbook m1 pro
Benchmark Mode Cnt Score Error Units
StringFormat.stringIntConcat avgt 15 6.541 ? 0.056 ns/op
StringFormat.stringIntFormat avgt 15 17.399 ? 0.133 ns/op
StringFormat.stringIntStringBuilder avgt 15 8.004 ? 0.063 ns/op
>From the above data, we can see that the implementation of fastpath reduces
>the performance difference between String.format and StringBuilder from 10
>times to 2~3 times.
The implementation of fastpath supports the following four specifiers, which
can appear at most twice and support a width of 1 to 9.
d
x
X
s
If necessary, we can add a few more.
Below is a comparison of performance numbers running on a MacBook M1, showing a
significant performance improvement.
-Benchmark Mode Cnt Score Error Units
(baseline)
-StringFormat.complexFormat avgt 15 895.954 ? 52.541 ns/op
-StringFormat.decimalFormat avgt 15 277.420 ? 18.254 ns/op
-StringFormat.stringFormat avgt 15 66.787 ? 2.715 ns/op
-StringFormat.stringIntFormat avgt 15 81.046 ? 1.879 ns/op
-StringFormat.widthStringFormat avgt 15 38.897 ? 0.114 ns/op
-StringFormat.widthStringIntFormat avgt 15 109.841 ? 1.028 ns/op
+Benchmark Mode Cnt Score Error Units (current
f925339e93fdf7a281462554ce5d73139bd0f0cd)
+StringFormat.complexFormat avgt 15 863.156 ? 42.140 ns/op
+StringFormat.decimalFormat avgt 15 287.342 ? 19.896 ns/op
+StringFormat.stringFormat avgt 15 6.738 ? 0.027 ns/op
+StringFormat.stringIntFormat avgt 15 17.046 ? 0.090 ns/op
+StringFormat.widthStringFormat avgt 15 8.993 ? 0.073 ns/op
+StringFormat.widthStringIntFormat avgt 15 17.602 ? 0.014 ns/op
-------------
Commit messages:
- String.format fastpath
Changes: https://git.openjdk.org/jdk/pull/19956/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19956&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8335366
Stats: 362 lines in 3 files changed: 356 ins; 0 del; 6 mod
Patch: https://git.openjdk.org/jdk/pull/19956.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/19956/head:pull/19956
PR: https://git.openjdk.org/jdk/pull/19956
