PERF: run post timings in background

This means that if a very large amount of registered users hit
a single topic we will handle it gracefully, even if db gets slow.

lib/hijack.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require_dependency 'method_profiler'
+
 # This module allows us to hijack a request and send it to the client in the deferred job queue
 # For cases where we are making remote calls like onebox or proxying files and so on this helps
 # free up a unicorn worker while the remote IO is happening
@@ -13,20 +15,19 @@ module Hijack
       request.env['discourse.request_tracker.skip'] = true
       request_tracker = request.env['discourse.request_tracker']
 
-      # unicorn will re-cycle env, this ensures we keep the original copy
-      env_copy = request.env.dup
-      request_copy = ActionDispatch::Request.new(env_copy)
+      # in the past unicorn would recycle env, this is not longer the case
+      env = request.env
+      request_copy = ActionDispatch::Request.new(env)
 
-      transfer_timings = MethodProfiler.transfer if defined? MethodProfiler
+      transfer_timings = MethodProfiler.transfer
 
       io = hijack.call
 
       Scheduler::Defer.later("hijack #{params["controller"]} #{params["action"]}") do
 
-        MethodProfiler.start(transfer_timings) if defined? MethodProfiler
-
+        MethodProfiler.start(transfer_timings)
         begin
-          Thread.current[Logster::Logger::LOGSTER_ENV] = env_copy
+          Thread.current[Logster::Logger::LOGSTER_ENV] = env
           # do this first to confirm we have a working connection
           # before doing any work
           io.write "HTTP/1.1 "
@@ -43,7 +44,7 @@ module Hijack
             instance.instance_eval(&blk)
           rescue => e
             # TODO we need to reuse our exception handling in ApplicationController
-            Discourse.warn_exception(e, message: "Failed to process hijacked response correctly", env: env_copy)
+            Discourse.warn_exception(e, message: "Failed to process hijacked response correctly", env: env)
           end
 
           unless instance.response_body || response.committed?
@@ -56,36 +57,40 @@ module Hijack
 
           headers = response.headers
           # add cors if needed
-          if cors_origins = env_copy[Discourse::Cors::ORIGINS_ENV]
-            Discourse::Cors.apply_headers(cors_origins, env_copy, headers)
+          if cors_origins = env[Discourse::Cors::ORIGINS_ENV]
+            Discourse::Cors.apply_headers(cors_origins, env, headers)
           end
 
           headers['Content-Length'] = body.bytesize
           headers['Content-Type'] = response.content_type || "text/plain"
           headers['Connection'] = "close"
 
-          status_string = Rack::Utils::HTTP_STATUS_CODES[instance.status.to_i] || "Unknown"
-          io.write "#{instance.status} #{status_string}\r\n"
+          status_string = Rack::Utils::HTTP_STATUS_CODES[response.status.to_i] || "Unknown"
+          io.write "#{response.status} #{status_string}\r\n"
 
           headers.each do |name, val|
             io.write "#{name}: #{val}\r\n"
           end
 
+          timings = MethodProfiler.stop
+          if timings && duration = timings[:total_duration]
+            io.write "X-Runtime: #{"%0.6f" % duration}\r\n"
+          end
+
           io.write "\r\n"
           io.write body
         rescue Errno::EPIPE, IOError
           # happens if client terminated before we responded, ignore
           io = nil
         ensure
-
+          MethodProfiler.clear
           Thread.current[Logster::Logger::LOGSTER_ENV] = nil
 
           io.close if io rescue nil
 
           if request_tracker
             status = instance.status rescue 500
-            timings = MethodProfiler.stop if defined? MethodProfiler
-            request_tracker.log_request_info(env_copy, [status, headers || {}, []], timings)
+            request_tracker.log_request_info(env, [status, headers || {}, []], timings)
           end
         end
       end