Added a new meta table to keep track of the last run job, this way th…

…e tasks are ensured to respect the interval even if there's no tasks in the queue.

generators/delayed_job/templates/migration.rb

@@ -13,9 +13,14 @@ def self.up
     end
 
     add_index :delayed_jobs, [:priority, :run_at], :name => 'delayed_jobs_priority'
+
+    create_table :delayed_jobs_meta, :force => true do |table|
+      table.datetime :last_run_at
+    end
   end
 
   def self.down
-    drop_table :delayed_jobs  
+    drop_table :delayed_jobs
+    drop_table :delayed_jobs_meta
   end
 end

lib/delayed/backend/active_record.rb

@@ -17,13 +17,18 @@ def dump_for_delayed_job
 module Delayed
   module Backend
     module ActiveRecord
+      class Meta < ::ActiveRecord::Base
+        include Delayed::Backend::Base
+        set_table_name :delayed_jobs_meta
+      end
       # A job object that is persisted to the database.
       # Contains the work object as a YAML field.
       class Job < ::ActiveRecord::Base
         include Delayed::Backend::Base
         set_table_name :delayed_jobs
 
         before_save :set_default_run_at
+        before_save :set_last_run_at_meta
 
         named_scope :ready_to_run, lambda {|worker_name, max_run_time|
           {:conditions => ['(run_at <= ? AND (locked_at IS NULL OR locked_at < ?) OR locked_by = ?) AND failed_at IS NULL', db_time_now, db_time_now - max_run_time, worker_name]}

lib/delayed/backend/base.rb

@@ -92,6 +92,14 @@ def attempt_to_load(klass)
       def set_default_run_at
         self.run_at ||= self.class.db_time_now
       end
+
+      def set_last_run_at_meta
+        if meta = Delayed::Meta.find(:last)
+          meta.update_attributes(:last_run_at => self.run_at)
+        else
+          Delayed::Meta.create(:last_run_at => self.run_at)
+        end
+      end
 
     end
   end

lib/delayed/backend/mongo_mapper.rb

@@ -19,6 +19,11 @@ def dump_for_delayed_job
 module Delayed
   module Backend
     module MongoMapper
+      class Meta
+        include MongoMapper::Document
+        include Delayed::Backend::Base
+        set_collection_name 'delayed_jobs_meta'
+      end
       class Job
         include ::MongoMapper::Document
         include Delayed::Backend::Base
@@ -35,6 +40,7 @@ class Job
         timestamps!
 
         before_save :set_default_run_at
+        before_save :set_last_run_at_meta
 
         ensure_index [[:priority, 1], [:run_at, 1]]
 

lib/delayed/worker.rb

@@ -28,10 +28,14 @@ class Worker
     def self.backend=(backend)
       if backend.is_a? Symbol
         require "delayed/backend/#{backend}"
-        backend = "Delayed::Backend::#{backend.to_s.classify}::Job".constantize
+        backend_job  = "Delayed::Backend::#{backend.to_s.classify}::Job".constantize
+        backend_meta = "Delayed::Backend::#{backend.to_s.classify}::Meta".constantize
+      end
+      @@backend = backend_job
+      silence_warnings do
+        ::Delayed.const_set(:Job, backend_job)
+        ::Delayed.const_set(:Meta, backend_meta)
       end
-      @@backend = backend
-      silence_warnings { ::Delayed.const_set(:Job, backend) }
     end
 
     def initialize(options={})
@@ -119,7 +123,15 @@ def run(job)
     end
 
     def self.run_at_set_interval
-      self.run_interval.seconds.since(Delayed::Job.last.run_at) if Delayed::Job.count > 0
+      self.run_interval.seconds.since(self.run_time_of_last_job) unless self.run_time_of_last_job.nil?
+    end
+
+    def self.run_time_of_last_job
+      if Delayed::Job.count > 0
+        Delayed::Job.last.run_at
+      else
+        Delayed::Meta.find(:first).last_run_at
+      end
     end
 
     # Reschedule the job in the future (when a job fails).