jruby (ext) loading left-overs to consider

[kares]

... left-overs from #5205

• do we force users extension authors to do a require 'jruby' ... loosely needed atm
  (most exts tend to have an explicit require 'jruby' or use the new load_ext mechanism)

• JRuby auto-loads the java library (since ~ 1.6/1.7) think about NOT auto loading require 'jruby'
  now, its auto-loaded from kernel which was likely not intentional (should only auto require 'java')?

• document extension loading (wiki): require 'jruby'; JRuby.load_ext('foo.bar.MyExtClass')

• need to propagate load_ext changes to gems we tend to boot often (on every run) ~ due RGs :
  jruby-openssl, jruby-readline, psych, jar-dependencies
  ... and get them to propagate releases (so this PR delivers the promised loading speed improvement)

[enebo]

@kares will load_ext work on 9.1.x? It is not unsurmountable if it won't but this would make it much easier for extensions to update. 9.1.x is probably living until beginning of 2019 at least.

[kares]

@enebo we could back-port if it makes sense ...
but than I am not sure we need that - all of these gems handle load_ext backwards compatibly.
your assumption would be that it would help adoption - migrating gems to an official way of ext loading?

9.1.x is probably living until beginning of 2019 at least.

that "long" for 9.1 - thought you guys do not plan on supporting multiple 2.x versions in parallel.

[enebo]

@kares I guess I did not realize load_ext worked on 9.1. If so then no reason to backport. Right now most exts I have written do this: 'Java::oj.OjLibrary.new.load(JRuby.runtime, false)'.

At this point I think we have reverted to the idea of supporting 2 versions only. The problem with only one 9.x is that we cannot just say 9.2.0.0 is out use it! We know it takes several point releases to iron over the work made (2.3->2.5 was larger than we actually planned since we skipped 2.4 too). I am hoping 9.2.x matures faster than 9.1.x but there has to be some overlap so people don't feel dropped and angry about it.

[kares]

OK, just to clarify - load_ext does not work in 9.1 (unless backported) but the way we add support for it a newer gems is backward compatible :

+if JRuby::Util.respond_to?(:load_ext) # JRuby 9.2
+  JRuby::Util.load_ext('org.jruby.ext.openssl.OpenSSL')
+else; require 'jruby'
+  org.jruby.ext.openssl.OpenSSL.load(JRuby.runtime)
+end

(JRuby::Util has existed as an internal pre-loaded piece to help boot - somehow resurrected the concept just so "internal" loading works even without require 'jruby') ... thus your ext would do the "official" way :

require 'jruby'
if JRuby.respond_to?(:load_ext)
  JRuby.load_ext('oj.OjLibrary')
else
  Java::oj.OjLibrary.new.load(JRuby.runtime, false)
end

BTW some questions still remain e.g. whether to remove require 'jruby' happening on JRuby boot -
no opinions there really other than loading "less" so eventually JRuby could also NOT auto require 'java' at some point in the future ... maybe :)

[enebo]

@kares thanks. I suppose for backwards compat we need to do new and old way anyways so this is some good boilerplate which should be on our wiki somewhere too.

[kares]

jar_dependencies has been updated already ^^ and now psych 3.0.3 is also in d18d98d
... so all the left-overs are handled -> JRuby shouldn't do any self reflection on its own, at least with its default commands such as gem, irb