added couch_rest backend adapter

lib/delayed/backend/couch_rest.rb

@@ -0,0 +1,72 @@
+require 'couchrest'
+
+#make sure database exists. If not create it.
+CouchRest::Server.new.database!('delayed_job')
+
+#extent couchrest to handle delayed_job serialization.
+class CouchRest::ExtendedDocument
+  def self.load_for_delayed_job(id)
+    (id)? get(id) : super 
+  end
+
+  def dump_for_delayed_job
+    "#{self.class};#{id}"
+  end
+end
+
+#couchrest adapter
+module Delayed
+  module Backend
+    module CouchRest
+      class Job < ::CouchRest::ExtendedDocument
+        include Delayed::Backend::Base
+        use_database ::CouchRest::Server.new.database('delayed_job')
+
+        property :priority
+        property :attempts
+        property :handler
+        property :run_at
+        property :locked_at
+        property :locked_by
+        property :failed_at
+        property :last_error
+        timestamps!
+
+        view_by(:locked_by, :run_at,
+                :map => "function(doc){" +
+                "          if(doc['couchrest-type'] == 'Delayed::Backend::CouchRest::Job' && doc.run_at) {" +
+                "            var locked_by = doc.locked_by || '';" +
+                "            emit([locked_by, doc.run_at], null);}" +
+                "        }")
+
+        set_callback :save, :before, :set_default_run_at
+        set_callback :save, :before, :set_default_attempts
+        set_callback :save, :before, :set_default_priority  
+
+        def self.db_time_now; Time.now; end    
+        def self.find_available(worker_name, limit = 5, max_run_time = Worker.max_run_time)
+          by_locked_by_and_run_at :start_key => [''], :end_key => ['', db_time_now], :limit => limit
+        end
+        def self.clear_locks!(worker_name)
+          docs = by_locked_by_and_run_at :startkey => [worker_name], :endkey => [worker_name, {}]
+          docs.each { |doc| doc.locked_by, doc.locked_at = nil, nil; }
+          database.bulk_save docs
+        end
+        def self.delete_all
+          database.bulk_save all.each { |doc| doc['_deleted'] = true }
+        end
+
+        def lock_exclusively!(max_run_time, worker = worker_name)
+          self.locked_at, self.locked_by = self.class.db_time_now, worker    
+          save
+        end
+        def set_default_priority
+          self.priority = 0 if priority.nil?
+        end
+        def set_default_attempts
+          self.attempts = 0 if attempts.nil?
+        end
+      end
+    end
+  end
+end