* syncing wip on connection cleaning

lib/jam_ruby/connection_cleaner.rb

@@ -22,22 +22,25 @@ class ConnectionCleaner
 
     @pg_conn.transaction do |conn|
 
+      # FOR UPDATE - lock the connection and related jam_sessions in question
+      conn.exec("SELECT user_id FROM connections LEFT OUTER JOIN music_sessions WHERE client_id = $1 ON connections.music_session_id = music_sessions.id FOR UPDATE", [client_id]) do |result|
 
-      conn.exec("DELETE FROM connections WHERE client_id = $1 RETURNING user_id", [client_id]) do |result|
-        if result.cmd_tuples == 0
-          # the client is already gone from the database... do nothing
+        conn.exec("DELETE FROM connections WHERE client_id = $1", [client_id]) do |result|
 
-        elsif result.cmd_tuples == 1
+          if result.cmd_tuples == 0
+            # the client is already gone from the database... do nothing
 
-          # if we did delete a row, check and see if any more connections for that user exist
-          # if we are down to zero, send out user gone message
-          conn.exec("SELECT count(user_id) FROM connections where user_id = $1", [result[0][0]]) do | result|
-            @mq_router.server_publish_to_user()
+          elsif result.cmd_tuples == 1
+
+            # if we did delete a row, check and see if any more connections for that user exist
+            # if we are down to zero, send out user gone message
+            conn.exec("SELECT count(user_id) FROM connections where user_id = $1", [result[0][0]]) do |result|
+              @mq_router.server_publish_to_user()
+            end
+          else
+            raise Exception 'uniqueness constraint has been lost on client_id'
           end
-        else
-          raise Exception 'uniqueness constraint has been lost on client_id'
         end
-
       end
 
     end
@@ -45,5 +48,4 @@ class ConnectionCleaner
   end
 
 
-
 end