Integrated: 8333086: Using Console.println is unnecessarily slow due to JLine initalization

[Jan Lahoda]

On Thu, 30 May 2024 13:50:33 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> 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.

This pull request has now been integrated.

Changeset: f7dbb98f
Author:    Jan Lahoda <jlahoda at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/f7dbb98fe69eb98f8544577d81550b4fd817864b
Stats:     226 lines in 2 files changed: 213 ins; 1 del; 12 mod

8333086: Using Console.println is unnecessarily slow due to JLine initalization

Reviewed-by: asotona, naoto

-------------

PR: https://git.openjdk.org/jdk/pull/19479