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Date: Thu, 20 Nov 2003 11:48:57 +0200
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Subject: Using do_alloca() instead of emalloc()
From: andi@zend.com (Andi Gutmans)

Hey,

I've been taking a look at the __autoload problem. During that time I saw 
that lots of places in the code (especially reflection API) use 
zend_str_tolower_dup().
In most of these cases it would be much more efficient to use 
do_alloca()/free_alloca() because that usually uses alloca() which 
allocates on the stack.
Simplified example from reflection API code:

lcname = zend_str_tolower_dup(name_str, name_len);

if (zend_hash_find(&ce->properties_info, lcname, name_len + 1, (void **) 
&property_info) == FAILURE) {
	efree(lcname);
	/* Error message */
	return;
}

efree(lcname);

This should really be:

lcname = do_alloca(name_len+1);
zend_str_tolower_copy(lcname, name_str, name_len+1);

if (zend_hash_find(&ce->properties_info, lcname, name_len + 1, (void **) 
&property_info) == FAILURE) {
	free_alloca(lcname);
	/* Error message */
	return;
}

free_alloca(lcname);

There are two times where you really shouldn't use do_alloca/free_alloca:
a) If you're in code which requires a regular malloc() don't use them (the 
fallback is emalloc()).
b) Only use them in functions which are about to return. They shouldn't be 
used in places like the main zend_execute loop because it would just make 
the stack grow more and more (in almost all cases where 
zend_str_tolower_dup() is being used, do_alloca/free_alloca are applicable).

I need to go away for the weekend now but it be cool if people here would 
at least take care of this in their code (such as reflection API code).

Thanks,

Andi