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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 22:30:50 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

Hello again,

In fact, there already was the skeleton in MHD to provide what I mean. I
attached a patch fil for the function MHD_set_response_options that
allows to override free() for the response buffer.
The change is quite simple in fact...

I didn't add tests to validate this patch because I wouldn't know where
to put them.
But with this change, I don't need to use MHD_RESPMEM_MUST_COPY anymore!

What do you think?


Le 19-07-21 à 16 h 10, Nicolas Mora a écrit :
> Hello,
> 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
> still).
> 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

Attachment: MHD_RO_FREE_FUNCTION.patch
Description: Text Data

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