That's what Apache does. Note, on most platforms MAP_ANON is equivalent to
mmmap-ing /dev/zero. Solaris for example does not provide MAP_ANON but using
fd=open(/dev/zero)
mmap(fd, ...)
close(fd)
works just fine.
----- Original Message -----
From: "Bruce Momjian" <pgman@candle.pha.pa.us>
To: "Igor Kovalenko" <Igor.Kovalenko@motorola.com>
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>; "mlw" <markw@mohawksoft.com>; "Marc G.
Fournier" <scrappy@hub.org>; <pgsql-hackers@postgresql.org>
Sent: Sunday, June 02, 2002 7:47 PM
Subject: Re: [HACKERS] HEADS UP: Win32/OS2/BeOS native ports
> Igor Kovalenko wrote:
> > It does not have to be anonymous. POSIX also defines shm_open(same
arguments
> > as open) API which will create named object in whatever location
corresponds
> > to shared memory storage on that platform (object is then grown to
needed
> > size by ftruncate() and the fd is then passed to mmap). The object will
> > exist in name space and can be detected by subsequent calls to
shm_open()
> > with same name. It is not really different from doing open(), but more
> > portable (mmap() on regular files may not be supported).
>
> Actually, I think the best shared memory implemention would be
> MAP_ANON | MAP_SHARED mmap(), which could be called from the postmaster
> and passed to child processes.
>
> While all our platforms have mmap(), many don't have MAP_ANON, but those
> that do could use it. You need MAP_ANON to prevent the shared memory
> from being written to a disk file.
>
> --
> Bruce Momjian | http://candle.pha.pa.us
> pgman@candle.pha.pa.us | (610) 853-3000
> + If your life is a hard drive, | 830 Blythe Avenue
> + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
>
