Instrument resque without forking

CHANGELOG.markdown

@@ -1,6 +1,7 @@
 # Unreleased
 - Fix undeclared logger in grape instruments (#510)
 - Drop guaranteed support for Rubies <= 2.4
+- Instrument Resque without relying on forking per job (#514)
 
 # 5.4.0
 * Add support for GoodJob (#506)

lib/scout_apm/agent.rb

@@ -208,7 +208,7 @@ def start_error_service_background_worker
 
       @error_service_background_worker = ScoutApm::BackgroundWorker.new(context, ERROR_SEND_FREQUENCY)
       @error_service_background_worker_thread = Thread.new do
-        @error_service_background_worker.start { 
+        @error_service_background_worker.start {
           periodic_work.run
         }
       end

lib/scout_apm/background_job_integrations/resque.rb

@@ -7,8 +7,7 @@ def name
 
       def present?
         defined?(::Resque) &&
-          ::Resque.respond_to?(:before_first_fork) &&
-          ::Resque.respond_to?(:after_fork)
+          ::Resque.respond_to?(:before_first_fork)
       end
 
       # Lies. This forks really aggressively, but we have to do handling
@@ -19,45 +18,29 @@ def forking?
       end
 
       def install
-        install_before_fork
-        install_after_fork
+        install_before_first_fork
+        install_instruments
       end
 
-      def install_before_fork
+      def install_before_first_fork
         ::Resque.before_first_fork do
           begin
+            # Don't check fork_per_job here in case some workers fork_per_job and some don't.
             if ScoutApm::Agent.instance.context.config.value('start_resque_server_instrument')
               ScoutApm::Agent.instance.start
               ScoutApm::Agent.instance.context.start_remote_server!(bind, port)
             else
               logger.info("Not starting remote server due to 'start_resque_server_instrument' setting")
             end
           rescue Errno::EADDRINUSE
-            ScoutApm::Agent.instance.context.logger.warn "Error while Installing Resque Instruments, Port #{port} already in use. Set via the `remote_agent_port` configuration option"
+            logger.warn "Error while Installing Resque Instruments, Port #{port} already in use. Set via the `remote_agent_port` configuration option"
           rescue => e
-            ScoutApm::Agent.instance.context.logger.warn "Error while Installing Resque before_first_fork: #{e.inspect}"
+            logger.warn "Error while Installing Resque before_first_fork: #{e.inspect}"
           end
         end
       end
 
-      def install_after_fork
-        ::Resque.after_fork do
-          begin
-            ScoutApm::Agent.instance.context.become_remote_client!(bind, port)
-            inject_job_instrument
-          rescue => e
-            ScoutApm::Agent.instance.context.logger.warn "Error while Installing Resque after_fork: #{e.inspect}"
-          end
-        end
-      end
-
-      # Insert ourselves into the point when resque turns a string "TestJob"
-      # into the class constant TestJob, and insert our instrumentation plugin
-      # into that constantized class
-      #
-      # This automates away any need for the user to insert our instrumentation into
-      # each of their jobs
-      def inject_job_instrument
+      def install_instruments
         ::Resque::Job.class_eval do
           def payload_class_with_scout_instruments
             klass = payload_class_without_scout_instruments
@@ -80,9 +63,12 @@ def port
       end
 
       def config
-        @config || ScoutApm::Agent.instance.context.config
+        @config ||= ScoutApm::Agent.instance.context.config
+      end
+
+      def logger
+        @logger ||= ScoutApm::Agent.instance.context.logger
       end
     end
   end
 end
-

lib/scout_apm/instruments/resque.rb

@@ -1,6 +1,15 @@
 module ScoutApm
   module Instruments
     module Resque
+      def before_perform_become_client(*args)
+        # Don't become remote client if explicitly disabled or if forking is disabled to force synchronous recording.
+        if config.value('start_resque_server_instrument') && forking?
+          ScoutApm::Agent.instance.context.become_remote_client!(bind, port)
+        else
+          logger.debug("Not becoming remote client due to 'start_resque_server_instrument' setting or 'fork_per_job' setting")
+        end
+      end
+
       def around_perform_with_scout_instruments(*args)
         job_name = self.to_s
         queue = find_queue
@@ -17,7 +26,6 @@ def around_perform_with_scout_instruments(*args)
           started_queue = true
           req.start_layer(ScoutApm::Layer.new('Job', job_name))
           started_job = true
-
           yield
         rescue => e
           req.error!
@@ -33,7 +41,28 @@ def find_queue
         return queue if self.respond_to?(:queue)
         return "unknown"
       end
+
+      private
+
+      def bind
+        config.value("remote_agent_host")
+      end
+
+      def port
+        config.value("remote_agent_port")
+      end
+
+      def config
+        @config ||= ScoutApm::Agent.instance.context.config
+      end
+
+      def logger
+        @logger ||= ScoutApm::Agent.instance.context.logger
+      end
+
+      def forking?
+        @forking ||= ENV["FORK_PER_JOB"] != "false"
+      end
     end
   end
 end
-