Ext func arg item seq can not be consumed 2 times

[Gabriel Petrovay]

If one tried to consume an external function argument item sequence 2 times, the 2nd time no more item is returned: next returns false and the item is NULL.

To reproduce, take any external module and in the "evaluate" implementation of a function do the following (make sure that the function receives a non non-empty sequence as the first parameter):

Item item;

Iterator_t iter = args[0]->getIterator();
iter->open();
iter->next(item);
iter->close();

// item is valid here

iter = args[0]->getIterator();
iter->open();
iter->next(item);
iter->close();

// item is NULL here

[Gabriel Petrovay (gabipetrovay)]

The problem might have to do with src\runtime\core\fncall_iterator.cpp:

10015 nbrinza is_open = true;
  9845 danielturcanu //if(open_count)
  9845 danielturcanu // theItemSequence->theChild->reset(theItemSequence->thePlanState);
  9845 danielturcanu open_count++;
  9845 danielturcanu }

...

 11584 markosza // theItemSequence->theChild->close(theItemSequence->thePlanState);

[Markos Zaharioudakis (markos-za)]

Gabriel, would it be ok with your use case if instead of calling getIterator() a second time, you reused the same iterator? Basically, the code would look something like this:

Item item;
Iterator_t iter = args[0] ->getIterator( );
iter->open();
iter->next(item);
iter->close();

// iter = args[0] ->getIterator( );
iter->open();
iter->next(item);
iter->close();

The only difference between the above code and your example is that I have commented-out the 2nd call to getIterator().

In general, it doesn't make sense to have more than one iterator on a ExtFuncArgItemSequence, unless the sequence is materialized, and then you would get a performance hit.

[Matthias Brantner (matthias-brantner)]

I think it's fine to restrict the API to only allow one iterator at a time. If the user has a use case
that requires two active iterators at a time, he should think about his use case and eventually
materialize in his code.

I'm going to approve the merge proposal.

[Gabriel Petrovay (gabipetrovay)]

What about this bug? Is it done?