Re: Use outerPlanState macro instead of referring to leffttree

Thanks for reviewing this patch.

On Sat, Jul 2, 2022 at 5:32 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Richard Guo <guofenglinux@gmail.com> writes:
> > In the executor code, we mix use outerPlanState macro and referring to
> > leffttree. Commit 40f42d2a tried to keep the code consistent by
> > replacing referring to lefftree with outerPlanState macro, but there are
> > still some outliers. This patch tries to clean them up.
>
> Seems generally reasonable, but what about righttree?  I find a few
> of those too with "grep".
>

Yes. We may do the same trick for righttree.


>
> Backing up a little bit, one thing not to like about the outerPlanState
> and innerPlanState macros is that they lose all semblance of type
> safety:
>
> #define innerPlanState(node)            (((PlanState *)(node))->righttree)
> #define outerPlanState(node)            (((PlanState *)(node))->lefttree)
>
> You can pass any pointer you want, and the compiler will not complain.
> I wonder if there's any trick (even a gcc-only one) that could improve
> on that.  In the absence of such a check, people might feel that
> increasing our reliance on these macros isn't such a hot idea.
>

Your concern makes sense. I think outerPlan and innerPlan macros share
the same issue. Not sure if there is a way to do the type check.


>
> Now, the typical coding pattern you've used:
>
>  ExecReScanHash(HashState *node)
>  {
> +       PlanState  *outerPlan = outerPlanState(node);
>
> is probably reasonably secure against wrong-pointer slip-ups.  But
> I'm less convinced about that for in-line usages in the midst of
> a function, particularly in the common case that the function has
> a variable pointing to its Plan node as well as PlanState node.
> Would it make sense to try to use the local-variable style everywhere?
>

Do you mean the pattern like below?

  outerPlanState(hashstate) = ExecInitNode(outerPlan(node), estate, eflags);

It seems that this pattern is mostly used when initializing child nodes
with ExecInitNode(), and most calls to ExecInitNode() are using this
pattern as a convention. Not sure if it's better to change them to
local-variable style.

Thanks
Richard