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
diff --git a/db/migrate/20090429014554_create_grader_messages.rb b/db/migrate/20090429014554_create_grader_messages.rb
new file mode 100644
--- /dev/null
+++ b/db/migrate/20090429014554_create_grader_messages.rb
@@ -0,0 +1,16 @@
+class CreateGraderMessages < ActiveRecord::Migration
+  def self.up
+    create_table :grader_messages do |t|
+      t.integer :grader_process_id
+      t.integer :command
+      t.string :options
+      t.integer :target_id
+      t.boolean :taken
+      t.timestamps
+    end
+  end
+
+  def self.down
+    drop_table :grader_messages
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -9,7 +9,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20090426131044) do
+ActiveRecord::Schema.define(:version => 20090429014554) do
 
   create_table "announcements", :force => true do |t|
     t.string   "author"
@@ -42,6 +42,16 @@
     t.datetime "updated_at"
   end
 
+  create_table "grader_messages", :force => true do |t|
+    t.integer  "grader_process_id"
+    t.integer  "command"
+    t.string   "options"
+    t.integer  "target_id"
+    t.boolean  "taken"
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
   create_table "grader_processes", :force => true do |t|
     t.string   "host",       :limit => 20
     t.integer  "pid"
diff --git a/test/fixtures/grader_messages.yml b/test/fixtures/grader_messages.yml
new file mode 100644
--- /dev/null
+++ b/test/fixtures/grader_messages.yml
@@ -0,0 +1,7 @@
+# Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html
+
+# one:
+#   column: value
+#
+# two:
+#   column: value
diff --git a/test/unit/grader_message_test.rb b/test/unit/grader_message_test.rb
new file mode 100644
--- /dev/null
+++ b/test/unit/grader_message_test.rb
@@ -0,0 +1,8 @@
+require 'test_helper'
+
+class GraderMessageTest < ActiveSupport::TestCase
+  # Replace this with your real tests.
+  test "the truth" do
+    assert true
+  end
+end