diff --git a/app/models/grader_message.rb b/app/models/grader_message.rb
new file mode 100644
--- /dev/null
+++ b/app/models/grader_message.rb
@@ -0,0 +1,85 @@
+class GraderMessage < ActiveRecord::Base
+
+  GRADE_SUBMISSION = 1
+  GRADE_TEST_REQUEST = 2
+  STOP = 3
+
+  def self.create_message(recipient, command, options=nil, target_id=nil)
+    recipient_id = recipient
+    if recipient == :all
+      recipient_id = -1
+    elsif recipient == :any
+      recipient_id = 0
+    end
+    
+    GraderMessage.create(:grader_process_id => recipient_id,
+                         :command => command,
+                         :options => options,
+                         :target_id => target_id,
+                         :taken => false)
+  end
+
+  def self.create_grade_submission(mode,submission)
+    GraderMessage.create_message(:any,
+                                 GraderMessage::GRADE_SUBMISSION,
+                                 mode,
+                                 submission.id)
+  end
+  
+  def self.create_grade_test_request(mode,test_request)
+    GraderMessage.create_message(:any,
+                                 GraderMessage::GRADE_TEST_REQUEST,
+                                 mode,
+                                 test_request.id)
+  end
+  
+  def self.create_stop(grader_process_id)
+    GraderMessage.create_message(grader_process_id,
+                                 GraderMessage::STOP)
+  end
+
+  def self.get_message_for(recipient_id, accepting_commands=:all)
+    command_conditions = 
+      GraderMessage.build_command_conditions(accepting_commands)
+    recp_conditions= "((`grader_process_id` = #{recipient_id.to_i})" +
+      " OR (`grader_process_id` = 0) OR (`grader_process_id` = -1))"
+
+    message = nil   # need this to bind message in do-block for transaction
+    begin
+      GraderMessage.transaction do
+        message = GraderMessage.find(:first, 
+                                     :order => "created_at", 
+                                     :conditions => 
+                                     "(`taken`=0)" + 
+                                     "AND (#{recp_conditions})" + 
+                                     " AND (#{command_conditions})",
+                                     :lock => true)
+        if message!=nil
+          message.taken = true
+          message.save!
+        end
+      end
+      
+    rescue
+      message = nil
+
+    end
+    
+    message
+  end
+  
+  protected
+  
+  def self.build_command_conditions(accepting_commands)
+    if accepting_commands==:all
+      return '(1=1)'
+    else
+      conds = []
+      accepting_commands.each do |command|
+        conds << "(`command` = #{command.to_i})"
+      end
+      return "(" + conds.join(" OR ") + ")"
+    end
+  end
+  
+end