String.format is widely used, and improving its performance is very meaningful.
This PR can significantly improve the performance of String.format. Sorry,
there are many changes, which will take a lot of time. I hope you can review it
patiently.
Improved performance includes the following:
## 1. Write directly during the parse process to reduce object allocation.
In the current Formatter implementation, some objects do not need to be
allocated, such as:
class Formatter {
public Formatter format(Locale l, String format, Object ... args) {
List<FormatString> fsa = parse(format);
// ...
}
static List<FormatString> parse(String s) {
ArrayList<FormatString> al = new ArrayList<>();
while (i < max) {
int n = s.indexOf('%', i);
if (n < 0) {
//
al.add(new FixedString(s, i, max));
}
}
}
}
In the process of parsing, the content that is not a Specifier is directly
appended without going through FixedString. By directly printing the parsed
FormatString object, there is no need to construct a `List<FormatString> fsa`
to store it.
## 2. Fast path print
Use specialized FormatString implementations for single-character and
single-width specifiers to avoid calling the large FormatSpecifier#print method.
## 3. String.format directly calls j.u.Formatter
String.format directly calls j.u.Formatter via SharedSecrets to improve
performance
-------------
Commit messages:
- speed up j.u.Formatter & String.format
Changes: https://git.openjdk.org/jdk/pull/20055/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20055&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8335791
Stats: 710 lines in 6 files changed: 586 ins; 60 del; 64 mod
Patch: https://git.openjdk.org/jdk/pull/20055.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/20055/head:pull/20055
PR: https://git.openjdk.org/jdk/pull/20055
