presto-main/src/main/java/io/prestosql/memory/QueryContext.java/QueryContext/acceptChildren
class QueryContext:    public <C, R> List<R> acceptChildren(QueryContextVisitor<C, R> visitor, C context)
    {
        return taskContexts.values()
                .stream()
                .map(taskContext -> taskContext.accept(visitor, context))
                .collect(toList());
    }