1 files changed, 50 insertions, 0 deletions
diff --git a/app/services/job_scheduler.rb b/app/services/job_scheduler.rb
new file mode 100644
index 00000000000..01c9bdbcc84
--- /dev/null
+++ b/app/services/job_scheduler.rb
@@ -0,0 +1,50 @@
+class JobScheduler
+
+  attr_reader :ident
+  def initialize(ident = nil)
+    @ident = ident
+  end
+
+  def start_work!
+    while run_next_job
+    end
+  end
+
+  private
+  def run_next_job
+    ActiveRecord::Base.transaction do
+      job = dequeue_job!
+
+      unless job
+        Rails.logger.info "Nothing to do."
+        return false
+      end
+
+      log = JobLog.new(job: job, scheduler: ident)
+
+      # Note that we may want to trade full consistency over
+      # making sure the database transactions are short.
+      #
+      # We could reschedule the job here and commit
+      # and only then execute the job.
+
+      begin
+        JobWorker.new(job).perform
+      ensure
+        log.save!
+        reschedule(job)
+      end
+
+      return true
+    end
+  end
+
+  def dequeue_job!
+    Job.lock('FOR UPDATE SKIP LOCKED').where('scheduled_for <= NOW()').order(:scheduled_for, :id).limit(1).first
+  end
+
+  def reschedule(job)
+    job.scheduled_for = Time.now() + 10.seconds
+    job.save!
+  end
+end