[ccan] [PATCH] btree: Add custom allocator interface.

[Stuart Longland]

On 08/02/16 10:45, Rusty Russell wrote:
> stuartl at longlandclan.id.au writes:
>> From: Stuart Longland <me at vk4msl.id.au>
>>
>> This provides a way for btree to be used with external allocator
>> libraries such as the tal or talloc modules.
> 
> Sure.  In my libraries I generally use a global allocator override;
> it's not thread-safe, but much easier to use in practice.
> 
> Since I don't use btree, I'm agnostic about it though!

Indeed, actually I'm half considering whether we make it a separate
module that `btree` (and others) can pull into their code.  There are
lots of cases where `tal` or `talloc` is desirable over the standard C
malloc/free.

> Minor nits below:
> …
>>  /*
>>   * If iter->node has parent, returns 1 and ascends the iterator such that
>> @@ -65,11 +68,19 @@ static int node_walk_forward(const struct btree_node *node,
>>  
>>  struct btree *btree_new(btree_search_t search)
>>  {
>> -	struct btree *btree = calloc(1, sizeof(struct btree));
>> -	struct btree_node *node = node_alloc(0);
>> +	return btree_new_with_alloc(search, &BTREE_DEFAULT_ALLOCATOR);
>> +}
>> +
>> +struct btree *btree_new_with_alloc(btree_search_t search,
>> +		const struct btree_allocator *alloc)
>> +{
>> +	struct btree *btree = (*(alloc->malloc))(alloc, sizeof(struct btree));
> 
> You can call a function pointer, so alloc->malloc(alloc, sizeof(struct btree));
> should work.  

Ahh, didn't know about that.  I presume a more recent C standard?  I'll
admit I had to look up the syntax for function pointers off Wikipedia as
I don't do it often enough.

(In fact, I don't do *C* often enough.)

> Lots of whitespace cleanups.  Not a problem, but prefer a separate patch
> for clarity.

Yep, I often do a whitespace cleanup first up and ordinarily do that as
a first commit.  I'll split these out.

> Put default_malloc and default_free above the BTREE_DEFAULT_ALLOCATOR
> definition, and you don't need to pre-declare them.

Will do.
Regards,
-- 
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
  ...it's backed up on a tape somewhere.

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