pg_atomic_exchange_u32() in ProcArrayGroupClearXid()
Hi!
While investigating ProcArrayGroupClearXid() code I wonder why do we have
this loop instead of plain pg_atomic_exchange_u32() call? Is it
intentional?
/*
* Now that we've got the lock, clear the list of processes waiting for
* group XID clearing, saving a pointer to the head of the list. Trying
* to pop elements one at a time could lead to an ABA problem.
*/
while (true)
{
nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
&nextidx,
INVALID_PGPROCNO))
break;
}
------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
On Fri, Sep 21, 2018 at 11:06 PM Alexander Korotkov
<a.korotkov@postgrespro.ru> wrote:
Hi!
While investigating ProcArrayGroupClearXid() code I wonder why do we have this loop instead of plain pg_atomic_exchange_u32() call?
We can use pg_atomic_exchange_u32 instead of a loop. In fact, clog
code uses pg_atomic_exchange_u32 for the same purpose. I think it is
better to make the code consistent at both places. Feel free to
change it, otherwise, I can take care of it in a few days time.
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
On Sat, Sep 22, 2018 at 9:55 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
On Fri, Sep 21, 2018 at 11:06 PM Alexander Korotkov
<a.korotkov@postgrespro.ru> wrote:While investigating ProcArrayGroupClearXid() code I wonder why do we
have this loop instead of plain pg_atomic_exchange_u32() call?
We can use pg_atomic_exchange_u32 instead of a loop. In fact, clog
code uses pg_atomic_exchange_u32 for the same purpose. I think it is
better to make the code consistent at both places. Feel free to
change it, otherwise, I can take care of it in a few days time.
Thank you for feedback. Pushed.
------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company