SIGINFO prints thread backtraces

lib/puma/cluster.rb

@@ -111,6 +111,17 @@ def hup
         Process.kill "HUP", @pid
       rescue Errno::ESRCH
       end
+
+      def info
+        Thread.list.each do |thread|
+          log "Thread TID-#{thread.object_id.to_s(36)} #{thread['label']}"
+          if thread.backtrace
+            log thread.backtrace.join("\n")
+          else
+            log "<no backtrace available>"
+          end
+        end
+      end
     end
 
     def spawn_workers
@@ -264,6 +275,10 @@ def worker(index, master)
         server.stop
       end
 
+      Signal.trap "SIGINFO" do
+        server.log_thread_status
+      end
+
       begin
         @worker_write << "b#{Process.pid}\n"
       rescue SystemCallError, IOError

lib/puma/server.rb

@@ -954,5 +954,16 @@ def self.current
     def shutting_down?
       @status == :stop || @status == :restart
     end
+
+    def log_thread_status
+      Thread.list.each do |thread|
+        @events.log "Thread TID-#{thread.object_id.to_s(36)} #{thread['label']}"
+        if thread.backtrace
+          @events.log thread.backtrace.join("\n")
+        else
+          @events.log "<no backtrace available>"
+        end
+      end
+    end
   end
 end

lib/puma/single.rb

@@ -102,6 +102,10 @@ def run
 
       @launcher.events.fire_on_booted!
 
+      Signal.trap "SIGINFO" do
+        server.log_thread_status
+      end
+
       begin
         server.run.join
       rescue Interrupt