Re: Expand palloc/pg_malloc API
| От | David G. Johnston |
|---|---|
| Тема | Re: Expand palloc/pg_malloc API |
| Дата | |
| Msg-id | CAKFQuwYtDc29Hhug3XwsvFFqWRSt3K7CAH5U21R7jZ1x0wVBwQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Expand palloc/pg_malloc API (Tom Lane <tgl@sss.pgh.pa.us>) |
| Ответы |
Re: Expand palloc/pg_malloc API
|
| Список | pgsql-hackers |
On Tue, Jul 26, 2022 at 2:32 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
2. I don't like the "palloc_ptrtype" name at all. I see that you
borrowed that name from talloc, but I doubt that's a precedent that
very many people are familiar with.
To me it sounds like it might
allocate something that's the size of a pointer, not the size of the
pointed-to object. I have to confess though that I don't have an
obviously better name to suggest. "palloc_pointed_to" would be
clear perhaps, but it's kind of long.
I agree that ptrtype reads "the type of a pointer".
This may not be a C-idiom but the pointed-to thing is a "reference" (hence pass by value vs pass by reference). So:
palloc_ref(myvariablepointer)
will allocate using the type of the referenced object. Just like _array and _obj, which name the thing being used as a size template as opposed to instantiate which seems more like another word for "allocate/palloc".
David J.
P.S.
Admittedly I'm still getting my head around reading pointer-using code (I get the general concept but haven't had to code them)....
- lockrelid = palloc(sizeof(*lockrelid));
+ lockrelid = palloc_ptrtype(lockrelid);
+ lockrelid = palloc_ptrtype(lockrelid);
// This definitely seems like an odd idiom until I remembered about short-lived memory contexts and the lost pointers are soon destroyed there.
So lockrelid (no star) is a pointer that has an underlying reference that the macro (and the orignal code) resolves via the *
I cannot reason out whether the following would be equivalent to the above:
lockrelid = palloc_obj(*lockrelid);
I assume not because: typeof(lockrelid) != (*lockrelid *)
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