Added method to Util module to clean up process records that don't have

a matching heartbeat record, indicating that they're no longer alive.

Added call to this new util method in the Schedule::Poller.poll_interval
method because the number of live processes is used as a multiplier for
the default wait interval.  Since the value for poll_interval is
memoized this call to 'cleanup_dead_process_records' should only be
called once at startup.

lib/sidekiq/scheduled.rb

@@ -75,6 +75,7 @@ module Sidekiq
       # We only do this if poll_interval is unset (the default).
       def poll_interval
         Sidekiq.options[:poll_interval] ||= begin
+          cleanup_dead_process_records
           pcount = Sidekiq.redis {|c| c.scard('processes') } || 1
           pcount * 15
         end

lib/sidekiq/util.rb

@@ -44,5 +44,21 @@ module Sidekiq
       end
     end
 
+    # Cleans up dead processes recorded in Redis.
+    def cleanup_dead_process_records
+      Sidekiq.redis do |conn|
+        procs = conn.smembers('processes').sort
+        heartbeats = conn.pipelined do
+          procs.each do |key|
+            conn.hget(key, 'beat')
+          end
+        end
+
+        heartbeats.each_with_index do |beat, i|
+          conn.srem('processes', procs[i]) if beat.nil?
+        end
+      end
+    end
+
   end
 end

test/test_util.rb

@@ -0,0 +1,58 @@
+require 'helper'
+require 'sidekiq/util'
+
+class TestUtil < Sidekiq::Test
+  class UtilClass
+    include Sidekiq::Util
+  end
+
+  describe 'util' do
+    before do
+      @orig_redis = Sidekiq.redis_pool
+      Sidekiq.redis = REDIS
+      Sidekiq.redis { |conn| conn.flushdb }
+    end
+
+    after do
+      Sidekiq.redis = @orig_redis
+    end
+
+    # In real code that manages the hash sets for process keys
+    # sets their expiration time to 60 seconds, so processes
+    # who don't have a set under their name are considered 'dead'
+    # because they haven't reported in
+    describe '#cleanup_dead_process_records' do
+      before do
+        # Set up some live and dead processes
+        @live_members = ['localhost-123', 'localhost-125']
+        @dead_members = ['localhost-124']
+
+        Sidekiq.redis do |conn|
+          conn.sadd('processes', @live_members + @dead_members)
+          # Add Heartbeats for the live processes
+          @live_members.each do |m|
+            conn.hset(m, 'beat', Time.now.to_f)
+          end
+        end
+
+        @util = UtilClass.new
+      end
+
+      after do
+        Sidekiq.redis do |conn|
+          conn.srem('processes', @live_members + @dead_members)
+          @live_members.each do |m|
+            conn.hdel(m, 'beat')
+          end
+        end
+      end
+
+      it "should remove dead process records" do
+        assert_equal 3, Sidekiq.redis{ |r| r.scard('processes') }
+        @util.cleanup_dead_process_records
+        still_alive = Sidekiq.redis{|r| r.smembers('processes')}
+        assert_equal still_alive.sort, @live_members.sort
+      end
+    end
+  end
+end