Too much on the stack?

[A. W. Dunstan]

Michael B Allen wrote:

> On Sat, 21 Jun 2003 13:05:15 -0400, Paul Pluzhnikov wrote:
>

>>> Why doesn't the following program overrun the stack?

>>
>> Why should it? Your 'ulimit' is apparently set higher than 6.5M ... The
>> only reason for this program to run out of stack is if it exceeds stack
>> ulimit, or comes close to where shared libraries are mapped. The 'ulimit
>> -s' is quite often unlimited, and shared libraries on Linux are usually
>> mapped up from 0x40000000.

>
> Interesting! I didn't know this. Ulimit is indeed set to 'unlimited'.
>

>> If you do not have gazillion of very large shared libraries, their
>> mappings are quite likely to stay below 0x50000000, which gives your
>> program quite a few more megabytes to grow.
>>

>>> How much is too much on the stack?

>>
>> That depends on your OS, and whether you ever plan to use your code in
>> multi-threaded environment, where stack sizes are significantly more
>> limited (Linux default is 8MB IIRC).

>
> The code is actually using pthreads. A thread will be calling this
> function.
>

The pthreads I've used (RH 7.3, glibc 2.2.5) allocated a separate 2MB stack
space for each thread. If you set your ulimit stack space to unlimited you
might have threads stepping on each other's stack.

--
Al Dunstan, Software Engineer
OptiMetrics, Inc.
3115 Professional Drive
Ann Arbor, MI 48104-5131

"To educate a man in mind and not in morals is to
educate a menace to society."
- Theodore Roosevelt

[Paul Pluzhnikov]

"A. W. Dunstan" <readHere@post.here> writes:

> The pthreads I've used (RH 7.3, glibc 2.2.5) allocated a separate 2MB stack
> space for each thread.

You are correct on this point.

> If you set your ulimit stack space to unlimited you
> might have threads stepping on each other's stack.

But quite mistaken on that one, for 2 reasons:

- 'ulimit -s' has *absolutely nothing* to with sizes of thread
stacks, and

- the thread manager puts a guard page (mprotect()ed with no access)
at the end of each 2MB stack region, so before a thread can
"step on other's stack", it will crash accessing the guard page.

That's not to say that a thread can't trash other thread's stack
due to a bad pointer ... But 'ulimit -s' has nothing to do with this.

Cheers,
--
In order to understand recursion you must first understand recursion.

[Chris Torek]

In article <uhe6ej0za.fsfYB8X@earthlink.net>
Paul Pluzhnikov <ppluzhnikov@earthlink.net> writes:

>- the thread manager puts a guard page (mprotect()ed with no access)
> at the end of each 2MB stack region, so before a thread can
> "step on other's stack", it will crash accessing the guard page.

Unless, of course, you skip right over the guard page.

If the page size is 4096 bytes and you allocate at least 8192
bytes (via "sub $8192,sp" or equivalent), you have a good chance
of doing just that.
--
In-Real-Life: Chris Torek, Wind River Systems (BSD engineering)
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) +1 801 277 2603
email: forget about it [url]http://67.40.109.61/torek/index.html[/url] (for the moment)
Reading email is like searching for food in the garbage, thanks to spammers.

[Cliff Fu Xuan Chen]

Hi All,

I'm a green hand on stream programming.

Does someone give me some good links or easy example on this?

Thanks in advance!

Cliff

[Cliff Fu Xuan Chen]

Hi All,

I'm a green hand on stream programming.

Does someone give me some good links or easy example on this?

Thanks in advance!

Cliff

[Andrew Gabriel]

In article <3F02AC70.8F1145B9@lucent.com>,
Cliff Fu Xuan Chen <fchen7@lucent.com> writes:

>
> Hi All,
>
> I'm a green hand on stream programming.
>
> Does someone give me some good links or easy example on this?

You don't say which UNIX, but if it's Solaris, then look at Sun's
STREAMS Programming Manual, [url]http://docs.sun.com/db/doc/806-6546[/url]
Much of this will be relevant to non-Solaris UNIXs with STREAMS
too, but the module loading and multi-threaded kernel parts will
be Solaris-specific.

PS, please turn off the HTML posting.

--
Andrew Gabriel
Consultant Software Engineer