Thread dumping signal implemented in Ruby code? No problem!

output

system ~/projects/jruby $ jruby -rjruby/thread_dump -e "Thread.new{ loop{ 'hello' } }.join"
^Z
[1]+  Stopped                 jruby -rjruby/thread_dump -e "Thread.new{ loop{ 'hello' } }.join"

system ~/projects/jruby $ bg
[1]+ jruby -rjruby/thread_dump -e "Thread.new{ loop{ 'hello' } }.join" &

system ~/projects/jruby $ kill -USR2 %1 ; sleep 1

Ruby Thread Dump
================
* Thread: main
* Stack:
RuntimeError: thread dump
    join at org/jruby/RubyThread.java:521
  (root) at -e:1

* Thread: RubyThread-1: -e:1
* Stack:
RuntimeError: thread dump
  __file__ at -e:1
      loop at org/jruby/RubyKernel.java:1343
  __file__ at -e:1
      call at org/jruby/RubyProc.java:270
      call at org/jruby/RubyProc.java:224

thread_dump.rb

require 'jruby'

begin
  handler = proc do
    cur_thread = Thread.current

    $stderr.puts "\nRuby Thread Dump\n================\n"

    thread_service = JRuby.runtime.thread_service
    trace_type = org.jruby.runtime.backtrace.TraceType

    for thread in thread_service.active_ruby_threads
      next if thread == cur_thread
      
      thread_r = JRuby.reference(thread)

      $stderr.puts "* Thread: #{thread_r.native_thread.name}"
      $stderr.puts "* Stack:"

      thread_r = JRuby.reference(thread)
      thread_context = thread_r.context

      unless thread_context
        $stderr.puts "  [dead]\n"
        next
      end

      ex = RuntimeError.new('thread dump')
      ex_r = JRuby.reference(ex)  

      gather = trace_type::Gather::NORMAL
      format = trace_type::Format::JRUBY

      ex_r.backtrace_data = gather.get_backtrace_data(thread_context, thread_r.native_thread, true)
      $stderr.puts format.print_backtrace(ex, false)

      $stderr.puts
    end
  end
  
  Signal.__jtrap_kernel(handler, 'USR2')
rescue ArgumentError
  $stderr.puts "failed handling USR2; 'jruby -J-XX:+UseAltSigs ...' to disable JVM's handler"
rescue Exception
  warn $!.message
  warning $!.backtrace
end

@headius Do you have something like this that would work for jruby-1.7.8? I got the following error when trying to run this:

NameError: no method 'getBacktraceData' for arguments (org.jruby.runtime.ThreadContext,java.lang.Thread,org.jruby.RubyBoolean.True) on Java::OrgJrubyRuntimeBacktrace::TraceType::Gather::
    from (irb):34:in `evaluate'
    from org/jruby/java/proxies/ArrayJavaProxy.java:138:in `each'
    from (irb):12:in `evaluate'
    from org/jruby/RubyProc.java:271:in `call'
    from (irb):50:in `evaluate'
    from org/jruby/RubyKernel.java:1123:in `eval'
    from org/jruby/RubyKernel.java:1519:in `loop'
    from org/jruby/RubyKernel.java:1284:in `catch'
    from org/jruby/RubyKernel.java:1284:in `catch'
    from /Users/snielsen/.rbenv/versions/jruby-1.7.8/bin/irb:13:in `(root)'