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

[Christian Grothoff]

Thanks, that looks good --- modulo re-using the value 0 in the
enumeration ;-), and lacking an update to the handbook/ChangeLog. I've
made those fixes and pushed the result to Git:

3d1b941137f9d8379e6e67d5abd57be5ae6ebe1a

Happy hacking!

Christian

On 7/22/19 4:33 AM, Nicolas Mora wrote:
> Sorry, the patch was inverted, here is a clean patch
> 
> Le 19-07-21 à 22 h 30, Nicolas Mora a écrit :
>> 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?
>>
>> /Nicolas
>>
>> 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: http://www.hoard.org/
>>>>> 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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