From e74dac7aebd453449d632c697cb05a277c998690 Mon Sep 17 00:00:00 2001
From: Eric Wong <normalperson@yhbt.net>
Date: Fri, 24 Apr 2009 13:36:49 -0700
Subject: SIGTT{IN,OU} {in,de}crements worker_processes

This allows dynamic tuning of the worker_processes count without
having to restart existing ones.  This also allows
worker_processes to be set to a low initial amount in the config
file for low-traffic deployments/upgrades and then scaled up as
the old processes are killed off.

Remove the proposed reexec_worker_processes from TODO since this
is far more flexible and powerful.

This will allow not-yet-existent third-party monitoring tools to
dynamically change and scale worker processes according to site
load without increasing the complexity of Unicorn itself.
---
 lib/unicorn.rb | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

(limited to 'lib/unicorn.rb')

diff --git a/lib/unicorn.rb b/lib/unicorn.rb
index 9510e4b..33be99a 100644
--- a/lib/unicorn.rb
+++ b/lib/unicorn.rb
@@ -101,7 +101,7 @@ module Unicorn
       raise ArgumentError, "no listeners" if LISTENERS.empty?
       self.pid = @config[:pid]
       build_app! if @preload_app
-      spawn_missing_workers
+      maintain_worker_count
       self
     end
 
@@ -192,7 +192,7 @@ module Unicorn
           case SIG_QUEUE.shift
           when nil
             murder_lazy_workers
-            spawn_missing_workers if respawn
+            maintain_worker_count if respawn
             master_sleep
           when :QUIT # graceful shutdown
             break
@@ -214,6 +214,10 @@ module Unicorn
             else
               logger.info "SIGWINCH ignored because we're not daemonized"
             end
+          when :TTIN
+            @worker_processes += 1
+          when :TTOU
+            @worker_processes -= 1 if @worker_processes > 0
           when :HUP
             respawn = true
             if @config.config_file
@@ -257,7 +261,8 @@ module Unicorn
     private
 
     # list of signals we care about and trap in master.
-    QUEUE_SIGS = [ :WINCH, :QUIT, :INT, :TERM, :USR1, :USR2, :HUP ].freeze
+    QUEUE_SIGS = [ :WINCH, :QUIT, :INT, :TERM, :USR1, :USR2, :HUP,
+                   :TTIN, :TTOU ].freeze
 
     # defer a signal for later processing in #join (master process)
     def trap_deferred(signal)
@@ -380,7 +385,6 @@ module Unicorn
     end
 
     def spawn_missing_workers
-      return if WORKERS.size == @worker_processes
       (0...@worker_processes).each do |worker_nr|
         WORKERS.values.include?(worker_nr) and next
         begin
@@ -399,6 +403,14 @@ module Unicorn
       end
     end
 
+    def maintain_worker_count
+      (off = WORKERS.size - @worker_processes) == 0 and return
+      off < 0 and return spawn_missing_workers
+      WORKERS.each_pair { |pid,w|
+        w.nr >= @worker_processes and kill_worker(:QUIT, pid) rescue nil
+      }
+    end
+
     # once a client is accepted, it is processed in its entirety here
     # in 3 easy steps: read request, call app, write app response
     def process_client(client)
-- 
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