Re: segfault in HEAD when too many nested functions call

Hi,

On 2017-07-21 20:17:54 -0400, Tom Lane wrote:
> > I dislike having the miscadmin.h include in executor.h - but I don't
> > quite see a better alternative.
>
> I seriously, seriously, seriously dislike that. You practically might as
> well put miscadmin.h into postgres.h. Instead, what do you think of
> requiring the individual ExecProcNode functions to perform
> CHECK_FOR_INTERRUPTS? Since they're already responsible for doing that
> if they have any long-running internal loops, this doesn't seem like a
> modularity violation. It is a risk for bugs-of-omission, sure, but so
> are a lot of other things that the per-node code has to do.

That'd work. Another alternative would be to move the inline definition
of ExecProcNode() (and probably a bunch of other related functions) into
a more internals oriented header. It seems likely that we're going to
add more inline functions to the executor, and that'd reduce the
coupling of external and internal users a bit.

> * I think the comments need more work. Am willing to make a pass over
> that if you want.

That'd be good, but let's wait till we have something more final.

> * In most places, if there's an immediate return-if-trivial-case test,
> we check stack depth only after that. There's no point in checking
> and then returning; either you already crashed, or you're at peak
> stack so far as this code path is concerned.

I went back/forth a bit on that one. The calling code might call other
functions that go deeper on the stack, which won't have the checks. Fine
with moving, just wanted to explain why I got there.

> * Can we redefine the ExecCustomScan function pointer as type
> ExecProcNodeCB, eliminating the unsightly cast in nodeCustom.c?

That'd change an "extension API", which is why I skipped it at this
point of the release cycle. It's not like we didn't have this type of
cast all over before. Ok, with changing it, but that's where I came
down.

> * The various callers of ExecScan() are pretty inconsistently coded.
> I don't care that much whether they use castNode() or just forcibly
> cast to ScanState*, but let's make them all look the same.

I tried changed the minimum, perfectly fine to move to castNode in a
wholesale manner. Btw, I really want to get rid of ExecScan(), at least
as an external function. Does a lot of unnecessary things in a lot of
cases, and makes branch prediction a lot worse. Not v10 stuff tho.

> * I believe the usual term for what these function pointers are is
> "methods", not "callbacks". Certainly we'd call them that if we
> were working in C++.

K.

- Andres