Horton

Re: Expand palloc/pg_malloc API

Peter Eisentraut <peter.eisentraut@enterprisedb.com>

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From: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
To: "David G. Johnston" <david.g.johnston@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-08-12T07:39:43Z
Lists: pgsql-hackers 
On 27.07.22 01:58, David G. Johnston wrote:
> 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);
> 
> // 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 think that would also work.

Ultimately, it would be more idiomatic (in Postgres), to write this as

lockrelid = palloc(sizeof(LockRelId));

and thus

lockrelid = palloc_obj(LockRelId);

Commits

  1. Add repalloc0 and repalloc0_array

  2. Expand palloc/pg_malloc API for more type safety

  3. Assorted examples of expanded type-safer palloc/pg_malloc API