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Avoid memory corruption in shared memory used by several processes?

Hi all,

I want to make data stored in-memory (not disk) available to several
processes. My concern is that poorly written C applications with
dangling pointers may(will) damage the data in this memory segment if
it is open to all, i.e. shared memory mapped into all processes memory
area.

I don't want to use TCP/IP client/server between the apps and a data
store process due to the overhead.

I don't want to start calculating checksums for all updates in a
shared memory area, since that means a lot of overhead.

Now my question:
Is it possible to expose just the interface of a data store component
and have that i/f shared between all processes who want to access the
data, and then have this shared interface make callbacks into a data
store process' private memory?

If yes, how do I achieve this? If not, why not?

Thanks for helping out
/Sune

Jul 6 '07 #1
12 4981
On Jul 5, 7:50 pm, Sune <sune_ahlg...@h otmail.comwrote :
Hi all,

I want to make data stored in-memory (not disk) available to several
processes. My concern is that poorly written C applications with
dangling pointers may(will) damage the data in this memory segment if
it is open to all, i.e. shared memory mapped into all processes memory
area.

I don't want to use TCP/IP client/server between the apps and a data
store process due to the overhead.

I don't want to start calculating checksums for all updates in a
shared memory area, since that means a lot of overhead.

Now my question:
Is it possible to expose just the interface of a data store component
and have that i/f shared between all processes who want to access the
data, and then have this shared interface make callbacks into a data
store process' private memory?

If yes, how do I achieve this? If not, why not?
Try news:comp.progr amming.threads

Jul 6 '07 #2
Sune wrote:
I want to make data stored in-memory (not disk) available to several
processes. My concern is that poorly written C applications with
dangling pointers may(will) damage the data in this memory segment if
it is open to all, i.e. shared memory mapped into all processes memory
area.
...
Is it possible to expose just the interface of a data store component
and have that i/f shared between all processes who want to access the
data, and then have this shared interface make callbacks into a data
store process' private memory?
Something like that is possible, although callbacks are used for
something different than what your describe. Standard C doesn't support
multiple processes, so this is off-topic in this newsgroup.

You need to check systems that support multiple processes. It may also
be possible, in some systems, to allow a single process to write an area
of memory and others to only read.
--
Thad
Jul 6 '07 #3
user923005 <dc*****@connx. comwrites:
On Jul 5, 7:50 pm, Sune <sune_ahlg...@h otmail.comwrote :
>I want to make data stored in-memory (not disk) available to several
processes.
[...]
Try news:comp.progr amming.threads
I suspect that's not the right place to ask. The OP asked about
processes, not threads; in many system, those are quite different
things.

It's probably better to ask in a newsgroup that deals with whatever
operating system the OP is using. At a guess, comp.unix.progr ammer
seems likely.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Jul 6 '07 #4
Keith Thompson wrote:
user923005 <dc*****@connx. comwrites:
>Sune <sune_ahlg...@h otmail.comwrote :
>>I want to make data stored in-memory (not disk) available to
several processes.

[...]
>Try news:comp.progr amming.threads

I suspect that's not the right place to ask. The OP asked about
processes, not threads; in many system, those are quite different
things.
To share memory you either need threads or some other arrangement
to specifically share a memory block. Threads are probably the
easiest initial mechanism.

--
<http://www.cs.auckland .ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfoc us.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net

--
Posted via a free Usenet account from http://www.teranews.com

Jul 6 '07 #5
CBFalconer <cb********@yah oo.comwrites:
Keith Thompson wrote:
>user923005 <dc*****@connx. comwrites:
>>Sune <sune_ahlg...@h otmail.comwrote :

I want to make data stored in-memory (not disk) available to
several processes.

[...]
>>Try news:comp.progr amming.threads

I suspect that's not the right place to ask. The OP asked about
processes, not threads; in many system, those are quite different
things.

To share memory you either need threads or some other arrangement
to specifically share a memory block. Threads are probably the
easiest initial mechanism.
<OT>
How exactly do threads help you share memory between proceses?

Unix-like systems typically have mechanisms to share memory between
processes; these mechanisms are independent of threads, which exist
within a single process.
</OT>

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Jul 6 '07 #6
Keith Thompson wrote:
CBFalconer <cb********@yah oo.comwrites:
.... snip ...
>
>To share memory you either need threads or some other arrangement
to specifically share a memory block. Threads are probably the
easiest initial mechanism.

<OT>
How exactly do threads help you share memory between proceses?

Unix-like systems typically have mechanisms to share memory between
processes; these mechanisms are independent of threads, which exist
within a single process.
</OT>
Because, at least in my mind, threads of a process all operate in
the same memory space, and all we have to do is control access.
Processes go to some trouble to keep the memory isolated.

--
<http://www.cs.auckland .ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfoc us.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net

--
Posted via a free Usenet account from http://www.teranews.com

Jul 6 '07 #7
CBFalconer <cb********@yah oo.comwrites:
Keith Thompson wrote:
>CBFalconer <cb********@yah oo.comwrites:
... snip ...
>>
>>To share memory you either need threads or some other arrangement
to specifically share a memory block. Threads are probably the
easiest initial mechanism.

<OT>
How exactly do threads help you share memory between proceses?

Unix-like systems typically have mechanisms to share memory between
processes; these mechanisms are independent of threads, which exist
within a single process.
</OT>

Because, at least in my mind, threads of a process all operate in
the same memory space, and all we have to do is control access.
Processes go to some trouble to keep the memory isolated.
Yes, and the OP specifically asked about sharing memory among
*processes*. Maybe threads are a better solution to his underlying
problem, but you should at least mention that you're suggesting an
alternative rather than answering his actual question.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Jul 6 '07 #8
"Keith Thompson" <ks***@mib.orgw rote in message
news:ln******** ****@nuthaus.mi b.org...
<OT>
How exactly do threads help you share memory between
proceses?

Unix-like systems typically have mechanisms to share memory
between processes; these mechanisms are independent of
threads, which exist within a single process.
Threads are sometimes referred to as lightweight processes.
</OT>
S

--
Stephen Sprunk "Those people who think they know everything
CCIE #3723 are a great annoyance to those of us who do."
K5SSS --Isaac Asimov
--
Posted via a free Usenet account from http://www.teranews.com

Jul 6 '07 #9
Stephen Sprunk wrote:
"Keith Thompson" <ks***@mib.orgw rote in message
><OT>
How exactly do threads help you share memory between
proceses?

Unix-like systems typically have mechanisms to share memory
between processes; these mechanisms are independent of
threads, which exist within a single process.

Threads are sometimes referred to as lightweight processes.
I believe Linux specifically creates processes and defeats the
memory isolation provisions in creating threads.

--
<http://www.cs.auckland .ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfoc us.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net

--
Posted via a free Usenet account from http://www.teranews.com

Jul 7 '07 #10

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