Consider these two programs:
public class SystemPrint {
public static void main(String... args) {
System.err.println("Hello!");
}
}
and:
public class IOPrint {
public static void main(String... args) {
java.io.IO.println("Hello!");
}
}
They do the same conceptual thing - write a text to the output. But,
`IO.println` delegates to `Console.println`, which then delegates to a
`Console` backend, and the default backend is currently based on JLine.
The issues is that JLine takes a quite a long time to initialize, and in a
program like this, JLine is not really needed - it is used to provide better
editing experience when reading input, but there's no reading in these programs.
For example, on my computer:
$ time java -classpath /tmp SystemPrint
Hello!
real 0m0,035s
user 0m0,019s
sys 0m0,019s
$ time java -classpath /tmp --enable-preview IOPrint
Hello!
real 0m0,165s
user 0m0,324s
sys 0m0,042s
The proposal herein is to delegate to the simpler `Console` backend from
`java.base` as long as the user only uses methods that print to output, and
switch to the JLine delegate when other methods (typically input) is used. Note
that while technically `writer()` is a method doing output, it will force JLine
initialization to avoid possible problems if the client caches the writer and
uses it after switching the delegates.
With this patch, I can get timing like this:
$ time java --enable-preview -classpath /tmp/ IOPrint
Hello!
real 0m0,051s
user 0m0,038s
sys 0m0,020s
which seems much more acceptable.
There is also #19467, which may reduce the time further.
A future work might focus on making JLine initialize faster, but avoiding JLine
initialization in case where we don't need it seems like a good step to me in
any case.
-------------
Commit messages:
- Cleanup, addint test.
- Using println correctly, flushing the java.base delegate before switching to
JLine.
- Force Terminal when writer is requested.
- Attempting to speedup start by delaying initialization of JLine until really
necessary.
Changes: https://git.openjdk.org/jdk/pull/19479/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19479&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8333086
Stats: 225 lines in 2 files changed: 212 ins; 1 del; 12 mod
Patch: https://git.openjdk.org/jdk/pull/19479.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/19479/head:pull/19479
PR: https://git.openjdk.org/jdk/pull/19479
