Support multiple listeners per-process

Use select(2) to multiplex non-blocking accept(2) calls between
them.  Additionally, aggressively make a bet after accepting
clients where we'll try to do a non-blocking accept(2) against
the full set of descriptors.  This is based on the assumption
that if we just accepted connections, we're probably reasonably
busy.

This should lead to lower latency under high load; but some
wasted cycles when requests come in intermitently.  By this same
logic, we don't really care for the thundering herd problem,
either; since it is only noticeable with many (hundreds) of
processes when most of them are idle.

1 files changed, 45 insertions, 17 deletions

diff --git a/lib/unicorn.rb b/lib/unicorn.rb
index a17ab2d..a301df6 100644
--- a/lib/unicorn.rb
+++ b/lib/unicorn.rb
@@ -52,12 +52,11 @@ module Unicorn
   # socket and a simple HttpServer.process_client function to
   # do the heavy lifting with the IO and Ruby.
   class HttpServer
-    attr_reader :workers, :logger, :host, :port, :timeout, :nr_workers
+    attr_reader :workers, :logger, :listeners, :timeout, :nr_workers
     
     DEFAULTS = {
       :timeout => 60,
-      :host => '0.0.0.0',
-      :port => 8080,
+      :listeners => %w(0.0.0.0:8080),
       :logger => Logger.new(STDERR),
       :nr_workers => 1
     }
@@ -74,7 +73,7 @@ module Unicorn
         instance_variable_set("@#{key.to_s.downcase}", value)
       end
 
-      @socket = Socket.unicorn_server_new("#{@host}:#{@port}", 1024)
+      @listeners.map! { |address| Socket.unicorn_server_new(address, 1024) }
     end
 
     # Does the majority of the IO processing.  It has been written in Ruby using
@@ -162,24 +161,53 @@ module Unicorn
     # to get this hash later.
     def start
       BasicSocket.do_not_reverse_lookup = true
-      @socket.unicorn_server_init if @socket.respond_to?(:unicorn_server_init)
+      @listeners.each do |sock|
+        sock.unicorn_server_init if sock.respond_to?(:unicorn_server_init)
+      end
 
       (1..@nr_workers).each do |worker_nr|
         pid = fork do
-          alive = true
+          nr, alive, listeners = 0, true, @listeners
           trap('TERM') { exit 0 }
-          trap('QUIT') { alive = false; @socket.close rescue nil }
+          trap('QUIT') do
+            alive = false
+            @listeners.each { |sock| sock.close rescue nil }
+          end
+
           while alive
             begin
-              client, addr = @socket.accept
-              client.unicorn_client_init
-              process_client(client)
-            rescue Errno::EMFILE
-              logger.error "too many open files"
-              sleep 0.5
-            rescue Errno::ECONNABORTED
-              # client closed the socket even before accept
-              client.close rescue nil
+              nr_before = nr
+              listeners.each do |sock|
+                begin
+                  client, addr = begin
+                    sock.accept_nonblock
+                  rescue Errno::EAGAIN
+                    next
+                  end
+                  nr += 1
+                  client.unicorn_client_init
+                  process_client(client)
+                rescue Errno::ECONNABORTED
+                  # client closed the socket even before accept
+                  client.close rescue nil
+                end
+                alive or exit(0)
+              end
+
+              # make the following bet: if we accepted clients this round,
+              # we're probably reasonably busy, so avoid calling select(2)
+              # and try to do a blind non-blocking accept(2) on everything
+              # before we sleep again in select
+              if nr > nr_before
+                listeners = @listeners
+              else
+                begin
+                  ret = IO.select(@listeners, nil, nil, nil) or next
+                  listeners = ret[0]
+                rescue Errno::EBADF
+                  exit(alive ? 1 : 0)
+                end
+              end
             rescue Object => e
               if alive
                 logger.error "Unhandled listen loop exception #{e.inspect}."
@@ -224,7 +252,7 @@ module Unicorn
 
     ensure
       trap('CHLD', old_chld_handler)
-      @socket.close rescue nil
+      @listeners.each { |sock| sock.close rescue nil }
     end
 
   end