src/Pure/Tools/build_process.scala

 
     def prepare_database(): Unit = {
       using_option(open_database()) { db =>
         db.transaction {
           for (table <- Data.all_tables) db.create_table(table)
+          db.lock_tables(Data.all_tables)
           Data.clean_build(db)
         }
         db.rebuild()
       }
     }

       val serial = if (changed.exists(identity)) State.inc_serial(serial0) else serial0
 
       stamp_worker(db, worker_uuid, serial)
       state.set_serial(serial).set_workers(read_workers(db))
     }
+
+
+    /* transaction_lock */
+
+    def transaction_lock[A](db: SQL.Database, body: => A): A =
+      db.transaction {
+        db.lock_tables(Build_Process.Data.all_tables)
+        body
+      }
   }
 }
 
 
 

 
   protected def synchronized_database[A](body: => A): A =
     synchronized {
       _database match {
         case None => body
-        case Some(db) => db.transaction { body }
+        case Some(db) => Build_Process.Data.transaction_lock(db, body)
       }
     }
 
   private def sync_database(): Unit =
     synchronized_database {