Support unique jobs: don't queue jobs that are already in the queue.

README.markdown

@@ -171,6 +171,16 @@ If your extension doesn't support scheduled job, you would need to extend the cu
       end
     end
 
+### Support for unique jobs
+
+Sometimes it doesn't make sense to queue a job if it's already there (with identical arguments). It would just lead to queue pollution. Unique jobs to the rescue:
+
+    create_fake_leaderboards:
+      cron: "30 6 * * 1"
+      args: 
+      unique_job: true
+      description: "This job will be queued only if the previous job is not in the queue anymore."
+
 
 Resque-web additions
 --------------------

lib/resque/scheduler.rb

@@ -130,13 +130,28 @@ def enqueue_from_config(config)
         klass_name = config['class'] || config[:class]
         params = args.is_a?(Hash) ? [args] : Array(args)
         queue = config['queue'] || config[:queue] || Resque.queue_from_class(constantize(klass_name))
-        # Support custom job classes like job with status
-        if (job_klass = config['custom_job_class']) && (job_klass != 'Resque::Job')
-          # custom job classes not supporting the same API calls must implement the #schedule method
-          constantize(job_klass).scheduled(queue, klass_name, *params)
+        unique_job = config['unique_job'] || config[:unique_job]
+
+        if (unique_job.to_s == 'true' || unique_job.to_s == 'yes') && job_exists_in_queue?(queue, klass_name, params)
+          log "Not adding unique job to queue #{queue} with #{params.inspect}"
         else
-          Resque::Job.create(queue, klass_name, *params)
-        end        
+          # Support custom job classes like job with status
+          if (job_klass = config['custom_job_class']) && (job_klass != 'Resque::Job')
+            # custom job classes not supporting the same API calls must implement the #schedule method
+            constantize(job_klass).scheduled(queue, klass_name, *params)
+          else
+            Resque::Job.create(queue, klass_name, *params)
+          end
+        end
+      end
+
+      # Test if a job exists for the given queue with the same arugments.
+      def job_exists_in_queue?(queue, klass_name, args)
+        queue_redis_name = "queue:#{queue}"
+        Resque.redis.lrange(queue_redis_name, 0, -1).any? do |queue_item|
+          parsed = Resque.decode(queue_item)
+          parsed["args"] == args
+        end
       end
 
       def rufus_scheduler

test/scheduler_test.rb

@@ -30,6 +30,26 @@ def test_enqueue_from_config_with_custom_class_job_in_the_resque_queue
     Resque::Scheduler.enqueue_from_config('cron' => "* * * * *", 'class' => 'SomeIvarJob', 'custom_job_class' => 'Resque::SchedulerTest::FakeJob', 'args' => "/tmp")
   end
 
+  def test_enqueue_from_config_doesnt_requeue_unique_jobs
+    # First queue "test" is empty.
+    assert_equal(0, Resque.redis.lrange("queue:test", 0, -1).size)
+
+    # Then, we add an unique job with argument /tmp/
+    Resque::Scheduler.enqueue_from_config('class' => 'SomeIvarJob', 'queue' => 'test',
+      'args' => '/tmp/', 'unique_job' => 'true')
+    assert_equal(1, Resque.redis.lrange("queue:test", 0, -1).size)
+
+    # Then, we try to add it again - but it won't be added.
+    Resque::Scheduler.enqueue_from_config('class' => 'SomeIvarJob', 'queue' => 'test',
+      'args' => '/tmp/', 'unique_job' => 'true')
+    assert_equal(1, Resque.redis.lrange("queue:test", 0, -1).size)
+
+    # Finally, we add a job with different arguments, and it will be added.
+    Resque::Scheduler.enqueue_from_config('class' => 'SomeIvarJob', 'queue' => 'test',
+      'args' => '/home/', 'unique_job' => 'true')
+    assert_equal(2, Resque.redis.lrange("queue:test", 0, -1).size)
+  end
+
   def test_enqueue_from_config_puts_stuff_in_the_resque_queue_when_env_match
     # The job should be loaded : its rails_env config matches the RAILS_ENV variable:
     ENV['RAILS_ENV'] = 'production'