polyglot - require 'git' failed by "threads not allowed in single-threaded mode"

[tisonkun]

After install gem ruby-git, I can require it in irb

$ irb
irb(main):001:0> require 'git'
=> true
irb(main):002:0>

However, when I try to access it in a plotglot context, it fails with "Exception in thread "main" threads not allowed in single-threaded mode (SecurityError)"

The code is

Context context = context = Context.newBuilder("ruby").allowAllAccess(true).build();
context.eval("ruby", "require 'git'");

and error logs

Exception in thread "main" java.lang.ExceptionInInitializerError
	at io.tison.polyglot.GitPlot.main(GitPlot.java:9)
Caused by: org.graalvm.polyglot.PolyglotException: threads not allowed in single-threaded mode (SecurityError)
	at <ruby>.block in Git::Lib#command(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git/lib.rb:954)
	at <ruby>.block in Git::Lib#with_custom_env_variables(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git/lib.rb:930)
	at <ruby>.Git::Lib#with_custom_env_variables(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git/lib.rb:927)
	at <ruby>.Git::Lib#command(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git/lib.rb:953)
	at <ruby>.Git::Lib#current_command_version(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git/lib.rb:865)
	at <ruby>.Git::Lib#meets_required_version?(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git/lib.rb:875)
	at <ruby>.<top (required)>(/Users/tison/.sdkman/candidates/java/1.0.0-rc-13-grl/jre/languages/ruby/lib/ruby/gems/2.4.0/gems/git-1.5.0/lib/git.rb:25)
	at <ruby>.<top (required)>(Unnamed:1)
	at <ruby>.(Unknown)
	at org.graalvm.polyglot.Context.eval(Context.java:361)
	at io.tison.polyglot.ruby.Ruby.<clinit>(Ruby.java:16)
	... 1 more

[tisonkun]

since I already set #allowAllAccess(true), I don't know how to resolve this issue.

[tisonkun]

Code around error log reported is

      with_custom_env_variables do
        command_thread = Thread.new do
          output = run_command(git_cmd, &block)
          exitstatus = $?.exitstatus
        end  
        command_thread.join
      end  

[chrisseaton]

@tisonkun sorry this issue is a little complicated at the moment. The relevant documentation is here

https://github.com/oracle/truffleruby/blob/master/doc/user/polyglot.md#embedded-configuration

When you use TruffleRuby from anything other there than the ruby launcher (or irb or whatever) you get an embedded configuration. This includes enabling single-threaded mode.

For what you want to do, probably just turn off single-threaded mode, by setting ruby.single-threaded to false.

As I say there's some complexity around this, so please try it and let me know, but that should already fix your issue. I can explain in more depth why this is needed if you're really interested.

[chrisseaton]

@eregon do you think it's still right that we're setting single-threaded in this configuration? I have a vague idea something changed in this area recently...

[tisonkun]

Add an option to workaround,

.option("ruby.single_threaded", "false")

and now process can fall through without exceptions.

However, the application becomes unable to exit when it executed the last statement.

The repository is here https://github.com/TisonKun/graal-polyglot-demo

[eregon]

@eregon do you think it's still right that we're setting single-threaded in this configuration? I have a vague idea something changed in this area recently...

At some point we made single-threaded default to embedded. This is still needed for js at least, until we have a more general solution in Truffle. cc @eleinadani

[eregon]

Maybe this should be more dynamic: we'd wait for the first thread creation and check if that succeed, then OK, otherwise turn on single-threaded mode and raise the exception.