presto-main/src/main/java/io/prestosql/operator/TaskContext.java/TaskContext/addCompletedDriverGroup
class TaskContext:    public void addCompletedDriverGroup(Lifespan driverGroup)
    {
        checkArgument(!driverGroup.isTaskWide(), "driverGroup is task-wide, not a driver group.");
        completedDriverGroups.add(driverGroup);
    }