SIGINFO prints thread backtraces (#1320)

lib/puma/cluster.rb

@@ -346,8 +346,8 @@ module Puma
       log "+ Changing to #{dir}"
       Dir.chdir dir
     end
-  
-    # Inside of a child process, this will return all zeroes, as @workers is only populated in 
+
+    # Inside of a child process, this will return all zeroes, as @workers is only populated in
     # the master process.
     def stats
       old_worker_count = @workers.count { |w| w.phase != @phase }

lib/puma/launcher.rb

@@ -325,6 +325,17 @@ module Puma
       log "- Goodbye!"
     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
+
     def set_process_title
       Process.respond_to?(:setproctitle) ? Process.setproctitle(title) : $0 = title
     end
@@ -441,6 +452,15 @@ module Puma
       rescue Exception
         log "*** SIGHUP not implemented, signal based logs reopening unavailable!"
       end
+
+      begin
+        Signal.trap "SIGINFO" do
+          log_thread_status
+        end
+      rescue Exception
+        # Not going to log this one, as SIGINFO is *BSD only and would be pretty annoying
+        # to see this constantly on Linux.
+      end
     end
 
     def require_rubygems_min_version!(min_version, feature)

test/helpers/integration.rb

@@ -97,7 +97,7 @@ class TestIntegration < Minitest::Test
   end
 
   # gets worker pids from @server output
-  def get_worker_pids(phase, size = WORKERS)
+  def get_worker_pids(phase = 0, size = WORKERS)
     pids = []
     re = /pid: (\d+)\) booted, phase: #{phase}/
     while pids.size < size

test/test_integration_cluster.rb

@@ -8,6 +8,20 @@ class TestIntegrationCluster < TestIntegration
     super
   end
 
+  def test_siginfo_thread_print
+    skip_unless_signal_exist? :INFO
+
+    cli_server("-w #{WORKERS} -q test/rackup/hello.ru")
+    worker_pids = get_worker_pids
+    output = []
+    t = Thread.new { output << @server.readlines }
+    Process.kill(:INFO, worker_pids.first)
+    Process.kill(:INT, @server.pid)
+    t.join
+
+    assert_match "Thread TID", output.join
+  end
+
   def test_usr2_restart
     _, new_reply = restart_server_and_listen("-q -w #{WORKERS} test/rackup/hello.ru")
     assert_equal "Hello World", new_reply
@@ -92,7 +106,7 @@ class TestIntegrationCluster < TestIntegration
     pid = cli_server("-w #{WORKERS} test/rackup/hello.ru").pid
 
     # Get the PIDs of the child workers.
-    worker_pids = get_worker_pids 0
+    worker_pids = get_worker_pids
 
     # Signal the workers to terminate, and wait for them to die.
     Process.kill :TERM, pid

test/test_integration_single.rb

@@ -84,4 +84,17 @@ class TestIntegrationSingle < TestIntegration
 
     assert_raises(Errno::ECONNREFUSED) { TCPSocket.new(HOST, @tcp_port) }
   end
+
+  def test_siginfo_thread_print
+    skip_unless_signal_exist? :INFO
+
+    cli_server("test/rackup/hello.ru")
+    output = []
+    t = Thread.new { output << @server.readlines }
+    Process.kill(:INFO, @server.pid)
+    Process.kill(:INT, @server.pid)
+    t.join
+
+    assert_match "Thread TID", output.join
+  end
 end

test/test_launcher.rb

@@ -60,4 +60,14 @@ class TestLauncher < Minitest::Test
     # assert no "/../" in path
     refute_match(%r{/\.\./}, puma_wild_location)
   end
+
+  def test_prints_thread_traces
+    events = Puma::Events.strings
+    l = Puma::Launcher.new(Puma::Configuration.new, events: events)
+
+    l.send(:log_thread_status)
+    events.stdout.rewind
+
+    assert_match "Thread TID", events.stdout.read
+  end
 end

test/test_puma_server.rb

@@ -9,7 +9,7 @@ class TestPumaServer < Minitest::Test
 
     @app = lambda { |env| [200, {}, [env['rack.url_scheme']]] }
 
-    @events = Puma::Events.new STDOUT, STDERR
+    @events = Puma::Events.strings
     @server = Puma::Server.new @app, @events
   end
 
@@ -280,9 +280,6 @@ EOF
   end
 
   def test_doesnt_print_backtrace_in_production
-    @events = Puma::Events.strings
-    @server = Puma::Server.new @app, @events
-
     @server.app = proc { |e| raise "don't leak me bro" }
     @server.leak_stack_on_error = false
     @server.add_tcp_listener @host, @port
@@ -298,7 +295,6 @@ EOF
   end
 
   def test_prints_custom_error
-    @events = Puma::Events.strings
     re = lambda { |err| [302, {'Content-Type' => 'text', 'Location' => 'foo.html'}, ['302 found']] }
     @server = Puma::Server.new @app, @events, {:lowlevel_error_handler => re}
 
@@ -314,7 +310,6 @@ EOF
   end
 
   def test_leh_gets_env_as_well
-    @events = Puma::Events.strings
     re = lambda { |err,env|
       env['REQUEST_PATH'] || raise("where is env?")
       [302, {'Content-Type' => 'text', 'Location' => 'foo.html'}, ['302 found']]