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Re: [libmicrohttpd] feature request: change malloc/calloc/free functions

From: Nicolas Mora
Subject: Re: [libmicrohttpd] feature request: change malloc/calloc/free functions
Date: Sun, 21 Jul 2019 16:10:13 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0


Thanks for the feedback. I totally agree with you on the performance
side. I myself don't use different malloc()/realloc()/free() than the
libc one.

The only reason I make this request is because of a bug a user of my
framework had because of my use of MHD_RESPMEM_MUST_FREE by default
which caused problems if the response is allocated with a malloc()
function incompatible with the libc one.

The workaround I found was to use MHD_RESPMEM_MUST_COPY instead, then
free the bdy response after calling MHD_create_response_from_buffer.
This works fine that some memory resource is wasted (not for long but

If not for the specific malloc/free function, would it be possible to
specify the free() function to deallocate the response body when using
MHD_RESPMEM_MUST_FREE? Like an option you could pass to MHD_Connection *
inside the MHD_AccessHandlerCallback function?

Le 19-07-21 à 15 h 44, Christian Grothoff a écrit :
> Hi Nicolas,
> Thanks for the proposal, but I don't think this kind of patch belongs
> into MHD. malloc() performance is not critical for MHD at all, as MHD
> hardly uses malloc(): We mostly use our own custom memory pool, usually
> on top of mmap(), to avoid fragmentation issues and to limit memory
> consumption per TCP connection.
> So I doubt you'd get _any_ performance delta by using Hoard. If I am
> wrong and you do have MHD-specific performance measurements that show
> that this is not premature optimization, please share them!
> Please also consider that there are allocation functions like
> strdup()/strndup(), and mixing allocators (malloc going to Hoard,
> strdup() to libc) is likely to end in disaster on free(). So in my view
> the only _good_ place to add the functions you propose (or Hoard itself)
> would be (GNU) libc.
> Happy hacking!
> Christian
> On 7/21/19 9:28 PM, Nicolas Mora wrote:
>> I happened to see that MHD doesn't allow to use different
>> malloc/calloc/free functions than the one provided by libc.
>> This would be useful if the underlying app using MHD uses different
>> allocating functions like Hoard:
>> More specifically, when using MHD_RESPMEM_MUST_FREE in a response
>> allocated with a different malloc() function, there would be problems.
>> I can submit a patch for it.
>> Basically, I'd do it by adding functions like this:
>> void MHD_set_alloc_funcs(MHD_malloc_t malloc_fn, MHD_calloc_t calloc_fn,
>> MHD_free_t free_fn);
>> void MHD_get_alloc_funcs(MHD_malloc_t * malloc_fn, MHD_calloc_t *
>> calloc_fn, MHD_free_t * free_fn);
>> I didn't see any use of realloc() in the source code, so I wouldn't
>> allow to change it.
>> Then, all internal call to malloc()/calloc()/free() would be replaced by
>> MHD_malloc()/MHD_calloc()/MHD_free()
>> How about that? Any feedback?
>> /Nicolas

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