Re: Add macros for ReorderBufferTXN toptxn

Thanks for the review!

On Mon, Mar 13, 2023 at 6:19 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
...
> Few comments:
> 1) Can we move the macros along with the other macros present in this
> file, just above this structure, similar to the macros added for
> txn_flags:
> /* Toplevel transaction for this subxact (NULL for top-level). */
> +#define isa_toptxn(rbtxn) (rbtxn->toptxn == NULL)
> +#define isa_subtxn(rbtxn) (rbtxn->toptxn != NULL)
> +#define get_toptxn(rbtxn) (isa_subtxn(rbtxn) ? rbtxn->toptxn : rbtxn)
>
> 2) The macro name can be changed to rbtxn_is_toptxn, rbtxn_is_subtxn
> and rbtxn_get_toptxn to keep it consistent with others:
> /* Toplevel transaction for this subxact (NULL for top-level). */
> +#define isa_toptxn(rbtxn) (rbtxn->toptxn == NULL)
> +#define isa_subtxn(rbtxn) (rbtxn->toptxn != NULL)
> +#define get_toptxn(rbtxn) (isa_subtxn(rbtxn) ? rbtxn->toptxn : rbtxn)
>
> 3) We could add separate comments for each of the macros:
> /* Toplevel transaction for this subxact (NULL for top-level). */
> +#define isa_toptxn(rbtxn) (rbtxn->toptxn == NULL)
> +#define isa_subtxn(rbtxn) (rbtxn->toptxn != NULL)
> +#define get_toptxn(rbtxn) (isa_subtxn(rbtxn) ? rbtxn->toptxn : rbtxn)
>

All the above are fixed as suggested.

> 4) We check if txn->toptxn is not null twice here both in if condition
> and in the assignment, we could retain the assignment operation as
> earlier to remove the 2nd check:
> - if (txn->toptxn)
> - txn = txn->toptxn;
> + if (isa_subtxn(txn))
> + txn = get_toptxn(txn);
>
> We could avoid one check again by:
> + if (isa_subtxn(txn))
> + txn = txn->toptxn;
>

Yeah, that is true, but I chose not to keep the original assignment in
this case mainly because then it is consistent with the other changed
code --- e.g. Every other direct member assignment/access of the
'toptxn' member now hides behind the macros so I did not want this
single place to be the odd one out. TBH, I don't think 1 extra check
is of any significance, but it is not a problem to change like you
suggested if other people also want it done that way.

------
Kind Regards,
Peter Smith.
Fujitsu Australia.