Catch signal TTIN and dump thread traces

lib/que/command_line_interface.rb

@@ -247,9 +247,21 @@ def parse(
         $stop_que_executable = false
         %w[INT TERM].each { |signal| trap(signal) { $stop_que_executable = true } }
 
+        trap("TTIN") do
+          puts 'Dumping thread traces:'
+          Thread.list.each do |t|
+            puts "## Thread TID-#{t.object_id.to_s(36)} #{t['label']}"
+            if t.backtrace
+              puts t.backtrace.join("\n")
+            else
+              puts "\tThread has no backtrace available"
+            end
+          end
+        end
+
         output.puts(
           <<~STARTUP
-            Que #{Que::VERSION} started worker process with:
+              Debug Que #{Que::VERSION} started worker process with:
               Worker threads: #{locker.workers.length} (priorities: #{locker.workers.map { |w| w.priority || 'any' }.join(', ')})
               Buffer size: #{locker.job_buffer.maximum_size}
               Queues: