[Expat-bugs] [ expat-Patches-1050446 ] custom allocators with state

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Patches item #1050446, was opened at 2004-10-19 19:30
Message generated for change (Comment added) made by nobody
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Category: None
Group: None
Status: Open
Resolution: Postponed
Priority: 5
Submitted By: Corey Brenner (coreybrenner)
Assigned to: Nobody/Anonymous (nobody)
Summary: custom allocators with state

Initial Comment:
It is sometimes necessary to use different memory 
allocation routines operating on one pool for different kinds 
of allocation, or to use different pools with one memory 
allocation routine (for instance, allocating data structures 
with a fixed-size allocator, and strings from a string heap 
utilizing a specialized string allocator). 
 
I have made a non-intrusive patch to the expat 
memory-handling suite which should be binary-compatible 
for those who are dynamic-linking the expat library. 
 
This patch allows one to provide "pool-allocation" function 
pointers, and a void pointer which is passed to the 
allocation routines as an extra argument, as part of the 
memory-handling suite structure. 
 
For instance: 
 
/* my_allocator prototype, wrapper functions */ 
extern int my_allocator(int op, void** pp, 
                                     size_t siz, void* pool); 
 
void* my_malloc (size_t siz, void* pool) { 
  void* p = NULL; 
  (void) my_allocator(OBTAIN, &p, siz, pool); 
  return p; 
} 
void* my_realloc (void* old, size_t siz, void* pool) { 
  (void) my_allocator(RESIZE, &old, siz, pool); 
  return old; 
} 
void my_free (void* mem, void* pool) { 
  (void) my_allocator(RETURN, &mem, 0, pool); 
} 
 
/* using it all */ 
int foo (void* pool) { 
        XML_Memory_Handling_Suite mhs = { 
                /* malloc_fcn */        NULL, 
                /* realloc_fcn */       NULL, 
                /* free_fcn */          NULL, 
                /* pool_malloc_fcn */   my_malloc, 
                /* pool_realloc_fcn */  my_realloc, 
                /* pool_free_fcn */     my_free, 
                /* pool */              NULL 
        }; 
 
	XML_Parser parser; 
 
	mhs.pool = pool; 
 
	parser = XML_Parser_Create_MM(NULL, &mhs, NULL); 
	if (!parser) { 
		die_horribly(); 
	} 
	/* ... */ 
} 
 
Note: XML_Memory_Handling_Suite has changed, but not 
in a way that will harm older programs which do not see 
these additions.  The memory-using macros provided in 
this patch first attempt to utilize the old allocators, if 
present, and then the new ones, so behavior for older 
programs is consistent. 
 
Documentation is updated to reflect the change. 

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Comment By: Nobody/Anonymous (nobody)
Date: 2004-12-21 10:24

Message:
Logged In: NO 

Did my patch not make it through?

I did submit one.  If not, please allow me to email it to 
someone.  My patch does this without breaking the 1.9x API, 
so it can be used currently.

Thanks,

--Corey

----------------------------------------------------------------------

Comment By: Karl Waclawek (kwaclaw)
Date: 2004-12-17 10:39

Message:
Logged In: YES 
user_id=290026

We are thinking of a future API change (after release 2.0)
where the memory allocation call-backs would gain an extra
parameter similar  tothe userData parameter set on the
parser.

This looks like your proposal, only more generic.

One use case we were thinking of is to prevent the
"million laughs" attack by monitoting memory usage per
parser instance.


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