Add random jitter to scheduler polling [#247]

Changes.md

@@ -1,3 +1,9 @@
+HEAD
+-----------
+
+- Add random jitter to scheduler to spread polls across POLL\_INTERVAL
+  window. [#247]
+
 2.0.2
 -----------
 

lib/sidekiq/cli.rb

@@ -69,7 +69,7 @@ module Sidekiq
       begin
         logger.info 'Starting processing, hit Ctrl-C to stop'
         @manager.start!
-        poller.poll!
+        poller.poll!(true)
         sleep
       rescue Interrupt
         logger.info 'Shutting down'

lib/sidekiq/scheduled.rb

@@ -18,8 +18,10 @@ module Sidekiq
 
       SETS = %w(retry schedule)
 
-      def poll
+      def poll(first_time=false)
         watchdog('scheduling poller thread died!') do
+          add_jitter if first_time
+
           # A message's "score" in Redis is the time at which it should be processed.
           # Just check Redis for the set of messages with a timestamp before now.
           now = Time.now.to_f.to_s
@@ -42,6 +44,17 @@ module Sidekiq
         end
       end
 
+      private
+
+      def add_jitter
+        begin
+          sleep(POLL_INTERVAL * rand)
+        rescue Celluloid::Task::TerminatedError
+          # Hit Ctrl-C when Sidekiq is finished booting and we have a chance
+          # to get here.
+        end
+      end
+
     end
   end
 end