presto-main/src/main/java/io/prestosql/execution/NodeTaskMap.java/NodeTaskMap/addNodeTask
class NodeTaskMap:    private NodeTasks addNodeTask(InternalNode node)
    {
        NodeTasks newNodeTasks = new NodeTasks(finalizerService);
        NodeTasks nodeTasks = nodeTasksMap.putIfAbsent(node, newNodeTasks);
        if (nodeTasks == null) {
            return newNodeTasks;
        }
        return nodeTasks;
    }