mini_racer_deadlock.rb

#!/usr/bin/env ruby
# Tested on Ruby 2.5.1
require 'mini_racer'

MiniRacer::Platform.set_flags!
$iso = MiniRacer::Isolate.new

# Some mindless JS to keep the runtime busy for a moment
MY_JS = <<~JS
  var foo = [];
  for (i=0; i<1000; i++) {
    foo[i] = 1;
    foo[i] ++;
  }
JS

# Make many contexts, exercise them, then dispose of them.
def many_contexts
  20.times {
    ctx = MiniRacer::Context.new(isolate: $iso)
    ctx.eval(MY_JS)
  }
end

def deadlocker
  threads = []
  20.times { |n|
    threads << Thread.new {
      GC.start(full_mark: true, immediate_sweep: true)
      GC.disable
    }

    threads << Thread.new {
      many_contexts
    }

    threads.each { |t| t.join }
    threads = []
    puts("still alive!")
  }
end

deadlocker
puts("Reached end of script successfully!")