Date: Thu, 15 Jan 1998 01:13:38 -0600 (CST) From: Joel Ray Holveck <joelh@gnu.org> To: tlambert@primenet.com Cc: tlambert@primenet.com, chrisy@flix.net, freebsd-hackers@FreeBSD.ORG Subject: Re: sharable static arrays? Message-ID: <199801150713.BAA04785@detlev.UUCP> In-Reply-To: <199801142007.NAA07464@usr06.primenet.com> (message from Terry Lambert on Wed, 14 Jan 1998 20:07:31 %2B0000 (GMT)) References: <199801142007.NAA07464@usr06.primenet.com>
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> OK. Sean was wrong and I was wrong.
Not wrong, if I understand properly, you just correctly answered a
different question than what I meant to ask.
> What you want is already in there. All original vnode data is
> shared between all processes. This includes static data. The
> program txt (executable code) is read-only. Data is read/write, but
> is marked copy-on-write. You do not take memory space for
> additional instances of the program, *unless* you write the data.
> If you do, it's copied. A page at a time. Uninitialized and
> allocated data are BSS data. This is allocated per process.
So, let me make sure I've got this straight:
int g_uninit; /* Global uninitialized */
int g_statinit = 1; /* Global statically initialized */
static int fs_g_uninit; /* File scope uninitialized */
static int fs_g_statinit = 1; /* File scope statically initialized */
const int g_const = 1; /* Global constant */
foo()
{
int local_uninit; /* Auto uninitialized */
int local_init = 4; /* Auto initialized */
static int ls_uninit; /* Local static uninitialized */
static int ls_init = 4; /* Local static initialized */
}
Now, I know the scoping rules, and I know the lifetime-of-data rules.
These are not my concern.
If I understand right:
g_statinit, fs_g_statinit, and ls_init are all stored in the data
segment, which is allocated and initialized at compile-time, and at
run-time is initially shared by all instances of the executable but is
copy-on-write (per page). (I did not originally realize that the data
segment was loaded copy-on-write; I had thought that a separate copy
was generated for each process.)
g_uninit, fs_g_uninit, and ls_uninit are all stored in the BSS
segment. Memory is reserved in the virtual address space at load
time, but not physically allocated until a page is written to during
run-time.
local_uninit and local_init are allocated on the stack at run-time.
local_init is initialized at run-time (by code generated by the
compiler) semimmediately after allocation.
Now, my question originally boiled down to this: does g_const get
allocated in text or data? I was assuming this would be significant
because I thought that text was allocated as shareable, but data had a
separate copy for each process. Now, realizing that data is
copy-on-write, I discover it is not an issue.
> I hope this answers all your questions, and the questions that the
> initial answers might have raised, so we can put this to rest. 8-).
All my questions raised by answers have been answered, and my original
question has been shown to be moot. I, too, will tire of this thread
before long.
I do appreciate the help from all.
Cheers,
joelh
--
Joel Ray Holveck - joelh@gnu.org - http://www.wp.com/piquan
Fourth law of programming:
Anything that can go wrong wi
sendmail: segmentation violation - core dumped
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