Re: PROC struct

From: Myron Scott <mscott(at)sacadia(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: PROC struct
Date: 2001-02-05 20:56:58
Message-ID: Pine.GSO.4.10.10102051251240.2779-100000@goldengate.kojoworldwide.com.
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On Mon, 5 Feb 2001, Tom Lane wrote:

> Myron Scott <mscott(at)sacadia(dot)com> writes:
> > May I suggest that watiHolder and waitLock pointers
> > in the proc struct in proc.h be changed from direct
> > pointers to SHMEM_OFFSET. They are both shared memory
> > structures in a shared memory structure and it would
> > be more consistent to make these SHMEM_OFFSET. Direct
> > pointers will be a problem if another process which is
> > not the result of a fork tries to attach to the shared memory.
>
> I don't really foresee that that's an issue --- any process
> we might conceivably want to have reading the shmem would be
> spawned by the postmaster anyway. I've actually been thinking
> about ripping out the shmem-offset-to-pointer-and-back conversions
> on the grounds of code simplification, readability, reliability
> (the compiler cannot detect whether you are casting a reconverted
> SHMEM_OFFSET to the wrong pointer type), and speed.
>
> regards, tom lane
>

Thanks for looking into this. I ran into this while working on a threaded
version of Postgres. I start a postmaster so I can use psql
and then start the multithreaded Postgres which attaches to the shared mem
created by the postmaster. This is not a big deal but maybe a note in the
header would be helpful to future tinkerers.

Thanks,

Myron Scott
mkscott(at)sacadia(dot)com

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