obstack_alloc & _obstack_newchunk

obstack_alloc & _obstack_newchunk

[J.]

Wednesday, February 23

Hello, I am looking into the GNU's obstack lib .

Unfortunatly it segfaults. According to a backtrace of the program stack
it goes down at obstack_newchunk_ . To be honest I am kind a stuck here.

There is enough free memory available since I am able to write this
message... The only thing I can come up with is that obstack_alloc trys
to add new memory to the address of string_obstack, which isn't properly
setup by moi.. ?

#include <stdio.h>
#include <string.h>
#include <obstack.h>

struct obstack string_obstack;

char *copystring(char *string);

int main(void) {
 char *orig = "to copy this string";
 char *str = NULL;

 str = copystring(orig);
 printf("%s\n", str);

 return 0;
}

char *copystring(char *string) {
 size_t len = 0;
 char *s = NULL;

 len = strlen(string) + 1;

 s = obstack_alloc(&string_obstack, len);
 memcpy(s, string, len);

 return s;
}

Thnkx..

J.

--
http://www.rdrs.net/

RE: obstack_alloc & _obstack_newchunk

[J.]

On Wed, 23 Feb 2005, Mariano Moreyra wrote:

> Hi J.
> 
> You need to init your obstack before using it
> Also, you need to declare this before calling obstack_init()
> 
> #define obstack_chunk_alloc malloc
> #define obstack_chunk_free free
> 
> So, your code would look like this:

<CUT>
...
</CUT>

Thank you for the complete answer.. !!

Cheers, J.

Re: obstack_alloc & _obstack_newchunk

[Rechberger Markus]

hmm what's the advantage of using the obstack_* functions? isn't
malloc already enough? never saw it in an application actually so I'm
just curious about it..

thanks
Markus

On Wed, 23 Feb 2005 14:37:17 +0100 (CET), J. <mailing-lists@xs4all.nl> wrote:
> On Wed, 23 Feb 2005, Mariano Moreyra wrote:
> 
> > Hi J.
> >
> > You need to init your obstack before using it
> > Also, you need to declare this before calling obstack_init()
> >
> > #define obstack_chunk_alloc malloc
> > #define obstack_chunk_free free
> >
> > So, your code would look like this:
> 
> <CUT>
> ...
> </CUT>
> 
> Thank you for the complete answer.. !!
> 
> Cheers, J.
> 
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Re: obstack_alloc & _obstack_newchunk

[J.]

On Wed, 23 Feb 2005, Rechberger Markus wrote:

> hmm what's the advantage of using the obstack_* functions? isn't
> malloc already enough? never saw it in an application actually so I'm
> just curious about it..
> 
> thanks
> Markus

Actually I was asking myself the exact same thing after I read that the
GCC compiler uses this memory allocation strategy. If you google for
obstack you will find a lot of programs using the obstack libs.

From what I understand upon till now, and please correct me if I am wrong:
obstack is a data stack that is used to create pooled memory allocation.
Memory allocation and deallocation, is said to be much faster because it's
done a pool at a time. Error-handling pools can be preallocated so that
programs can make good recovery's if no more regular memory is available.
The lifespan of a memory pool can be crontrolled like the way the apache
webserver does e.g. `Apache Portable Runtime'. 

For me personally I don't think I will use this strategy's because I
simply don't need it, but it is still interesting to look into it
because it requires me to actually think about how memory allocation works
and what the options are.

J.

> > On Wed, 23 Feb 2005, Mariano Moreyra wrote:
> > > Hi J.
> > >
> > > You need to init your obstack before using it
> > > Also, you need to declare this before calling obstack_init()
> > >
> > > #define obstack_chunk_alloc malloc
> > > #define obstack_chunk_free free
> > >
> > > So, your code would look like this:
> > 
> > <CUT>
> > ...
> > </CUT>
> > 
> > Thank you for the complete answer.. !!
> > 
> > Cheers, J.
> > -
--
http://www.rdrs.net/