FEATURE: set UNICORN_STATS_SOCKET_DIR for status socket

eg:

sam@ubuntu stats_sockets % socat - UNIX-CONNECT:9622.sock
gc_stat
{"count":46,"heap_allocated_pages":2459,"heap_sorted_length":2460,"heap_allocatable_pages":0,"heap_available_slots":1002267,"heap_live_slots":647293,"heap_free_slots":354974,"heap_final_slots":0,"heap_marked_slots":503494,"heap_swept_slots":498773,"heap_eden_pages":2459,"heap_tomb_pages":0,"total_allocated_pages":2459,"total_freed_pages":0,"total_allocated_objects":4337014,"total_freed_objects":3689721,"malloc_increase_bytes":6448248,"malloc_increase_bytes_limit":29188387,"minor_gc_count":36,"major_gc_count":10,"remembered_wb_unprotected_objects":19958,"remembered_wb_unprotected_objects_limit":39842,"old_objects":462019,"old_objects_limit":895782,"oldmalloc_increase_bytes":6448696,"oldmalloc_increase_bytes_limit":19350882}

Gemfile.lock

@@ -140,7 +140,7 @@ GEM
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
     jwt (1.5.6)
-    kgio (2.10.0)
+    kgio (2.11.0)
     libv8 (5.3.332.38.5)
     listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
@@ -272,7 +272,7 @@ GEM
       activesupport (= 4.2.8)
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
-    raindrops (0.17.0)
+    raindrops (0.18.0)
     rake (11.3.0)
     rake-compiler (0.9.9)
       rake
@@ -380,7 +380,7 @@ GEM
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.7.1)
-    unicorn (5.2.0)
+    unicorn (5.3.0)
       kgio (~> 2.6)
       raindrops (~> 0.7)
     uniform_notifier (1.10.0)

config/unicorn.conf.rb

@@ -36,6 +36,24 @@ preload_app true
 # fast LAN.
 check_client_connection false
 
+@stats_socket_dir = ENV["UNICORN_STATS_SOCKET_DIR"]
+
+def clean_up_stats_socket(server, pid)
+  if @stats_socket_dir.present?
+    name = "#{@stats_socket_dir}/#{pid}.sock"
+    FileUtils.rm_f(name)
+    server.logger.info "Cleaned up stats socket at #{name}"
+  end
+end
+
+def start_stats_socket(server)
+  if @stats_socket_dir.present?
+    name = "#{@stats_socket_dir}/#{Process.pid}.sock"
+    StatsSocket.new(name).start
+    server.logger.info "Started stats socket at #{name}"
+  end
+end
+
 initialized = false
 before_fork do |server, worker|
 
@@ -51,6 +69,18 @@ before_fork do |server, worker|
     # router warm up
     Rails.application.routes.recognize_path('abc') rescue nil
 
+    if @stats_socket_dir.present?
+      server.logger.info "Initializing stats socket at #{@stats_socket_dir}"
+      begin
+        FileUtils.mkdir_p @stats_socket_dir
+        FileUtils.rm_f Dir.glob("#{@stats_socket_dir}/*.sock")
+        require 'stats_socket'
+        start_stats_socket(server)
+      rescue => e
+        server.logger.info "Failed to initialize stats socket dir #{e}"
+      end
+    end
+
     # get rid of rubbish so we don't share it
     GC.start
 
@@ -75,6 +105,11 @@ before_fork do |server, worker|
 
       require 'demon/sidekiq'
 
+      if @stats_socket_dir
+        Demon::Sidekiq.after_fork do
+          start_stats_socket(server)
+        end
+      end
       Demon::Sidekiq.start(sidekiqs)
 
       Signal.trap("SIGTSTP") do
@@ -168,12 +203,17 @@ before_fork do |server, worker|
   sleep 1
 end
 
+after_worker_exit do |server, worker, status|
+  clean_up_stats_socket(server, status.pid)
+end
+
 after_fork do |server, worker|
+  start_stats_socket(server)
+
   # warm up v8 after fork, that way we do not fork a v8 context
   # it may cause issues if bg threads in a v8 isolate randomly stop
   # working due to fork
   Discourse.after_fork
-
   begin
     PrettyText.cook("warm up **pretty text**")
   rescue => e

lib/demon/sidekiq.rb

@@ -6,6 +6,10 @@ class Demon::Sidekiq < Demon::Base
     "sidekiq"
   end
 
+  def self.after_fork(&blk)
+    blk ? (@blk=blk) : @blk
+  end
+
   private
 
   def suppress_stdout
@@ -17,6 +21,8 @@ class Demon::Sidekiq < Demon::Base
   end
 
   def after_fork
+    Demon::Sidekiq.after_fork&.call
+
     STDERR.puts "Loading Sidekiq in process id #{Process.pid}"
     require 'sidekiq/cli'
     # CLI will close the logger, if we have one set we can be in big