Nokogiri blocks Ruby threads

result.log

I, [2020-03-07T14:40:36.587947 #90282]  INFO -- : *** Threaded ***
I, [2020-03-07T14:40:36.588335 #90282]  INFO -- : Still running
I, [2020-03-07T14:40:36.588399 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.588566 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589041 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589079 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589113 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589138 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589157 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589175 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:36.589203 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:53.202677 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:40:53.202883 #90282]  INFO -- : 15.884452   0.731071  16.615523 ( 16.614189)
I, [2020-03-07T14:40:36.589230 #90282]  INFO -- : Start Nokogiri
I, [2020-03-07T14:40:58.180972 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:40:55.004381 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:04.129960 #90282]  INFO -- : 26.442706   1.077119  27.519825 ( 27.540618)
I, [2020-03-07T14:40:39.136656 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:01.510371 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:09.359079 #90282]  INFO -- : 31.558369   1.183865  32.742234 ( 32.770588)
I, [2020-03-07T14:41:01.471189 #90282]  INFO -- : 20.684099   0.879757  21.563856 ( 24.860487)
I, [2020-03-07T14:41:07.811329 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:12.403081 #90282]  INFO -- : 29.409876   0.920205  30.330081 ( 30.409325)
I, [2020-03-07T14:41:12.425036 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:12.425155 #90282]  INFO -- : 19.399526   0.596986  19.996512 ( 20.026801)
I, [2020-03-07T14:41:09.358970 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:09.359113 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:04.129855 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:12.425377 #90282]  INFO -- : 34.518372   1.281099  35.799471 ( 35.835193)
I, [2020-03-07T14:41:12.279499 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:12.425487 #90282]  INFO -- : 34.490696   1.224212  35.714908 ( 35.778546)
I, [2020-03-07T14:41:12.402922 #90282]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:12.425627 #90282]  INFO -- : 25.617177   0.803064  26.420241 ( 26.481769)
I, [2020-03-07T14:41:12.425700 #90282]  INFO -- : 16.899154   0.489671  17.388825 ( 17.421087)
I, [2020-03-07T14:41:12.425754 #90282]  INFO -- : *** Forked ***
I, [2020-03-07T14:41:12.437300 #90311]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.437680 #90312]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.438253 #90313]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.438845 #90314]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.439781 #90315]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.440355 #90316]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.441231 #90317]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.442495 #90318]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.443786 #90319]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:12.445278 #90320]  INFO -- : Start Nokogiri
I, [2020-03-07T14:41:13.429324 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:14.430136 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:15.430589 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:16.431122 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:17.433490 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:18.445574 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:19.449898 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:20.454168 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:21.457702 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:22.457894 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:23.459269 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:24.462634 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:25.136144 #90312]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.140289 #90312]  INFO -- : 7.455782   1.017214   8.472996 ( 12.701245)
I, [2020-03-07T14:41:25.152517 #90313]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.153942 #90313]  INFO -- : 7.452782   1.016807   8.469589 ( 12.714258)
I, [2020-03-07T14:41:25.164082 #90318]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.168981 #90316]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.171387 #90318]  INFO -- : 7.449637   1.019224   8.468861 ( 12.726622)
I, [2020-03-07T14:41:25.173028 #90316]  INFO -- : 7.429858   0.999727   8.429585 ( 12.731311)
I, [2020-03-07T14:41:25.181784 #90314]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.183468 #90314]  INFO -- : 7.462105   1.025580   8.487685 ( 12.743272)
I, [2020-03-07T14:41:25.194311 #90317]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.195826 #90317]  INFO -- : 7.456276   1.015231   8.471507 ( 12.753052)
I, [2020-03-07T14:41:25.205521 #90311]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.207145 #90311]  INFO -- : 7.465108   1.040545   8.505653 ( 12.768246)
I, [2020-03-07T14:41:25.225940 #90315]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.227715 #90315]  INFO -- : 7.440923   1.011682   8.452605 ( 12.786527)
I, [2020-03-07T14:41:25.323806 #90319]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.329500 #90319]  INFO -- : 7.457472   0.966802   8.424274 ( 12.882557)
I, [2020-03-07T14:41:25.356879 #90320]  INFO -- : Done with Nokogiri
I, [2020-03-07T14:41:25.358468 #90320]  INFO -- : 7.431287   0.962229   8.393516 ( 12.910682)
I, [2020-03-07T14:41:25.466682 #90282]  INFO -- : Still running
I, [2020-03-07T14:41:26.467385 #90282]  INFO -- : Done

test.rb

require 'pathname'
require 'nokogiri'
require 'benchmark'
require 'logger'

def format_xslt
  file = File.open(Pathname.new("app").join("xslt", "xml-json", "isbn.xsl"), "rb")
  format_xslt = Nokogiri::XSLT(
    file
  )
  file.close
  format_xslt
end

def run
  $logger.info "Start Nokogiri"
  bench = Benchmark.measure do
    format_xslt.transform(xml_document).to_xml.tap { $logger.info "Done with Nokogiri" }
  end
  $logger.info bench.to_s.strip
end

def xml_document
  Nokogiri::XML(File.read(ARGV[0]))
end

$logger = Logger.new(STDOUT)

$logger.info "*** Threaded ***"
$running = true
t = Thread.new do
  while $running
    $logger.info "Still running"
    sleep 1
  end
end

threads = 10.times.map do
  Thread.new { run }
end
threads.each(&:join)

$logger.info "*** Forked ***"

10.times.map do
  fork { run }
end

Process.waitall
$running = false
t.join
$logger.info "Done"