[gst-devel] [gst-cvs] tpm gstreamer: gstreamer/ gstreamer/gst/

[Stefan Kost]

David Schleef schrieb:
> On Wed, Nov 07, 2007 at 07:53:44AM +0100, Stefan Kost wrote:
>> Hi,
>>
>> Quoting Tim Müller <t.i.m at zen.co.uk>:
>>
>>> On Tue, 2007-11-06 at 21:46 +0200, Stefan Kost wrote:
>>>
>>>>> * gst/gstdebugutils.c: (debug_dump_element),
>>>>>   (_gst_debug_bin_to_dot_file), (_gst_debug_bin_to_dot_file_with_ts):
>>>>>   Don't use VLAs which is a C99ism and throws off MSVC (#493983).
>>>> Wouldn't that be a use case of g_alloca ?
>>> g_alloca() would have been a possibility too, yes.  But since the patch
>>> provided used g_malloc() and I personally have a strong dislike against
>>> g_alloca() and we don't use it anywhere else in the core, I did not
>>> change it.
>>>
>> We were using it a.g. in alsa. And we should us it more. GStreamer  
>> causes quite a lot of memory fragmentation. I can rewrite this to do  
>> better in the next cycle.
> 
> GStreamer, as well as a sizeable percentage of other projects,
> have a long-standing rule against not using alloca(), ever.  Few
> people know the detailed rules of when it's safe to use, leading
> to maintenence problems.  One could write down some simpler rules,
> but all those cases are better served by local variables or using
> malloc.
> 
> Also, memory fragmentation is a property of the libc allocator, not
> GStreamer.  If GStreamer's allocator usage patterns cause problems
> for the allocator, that's a bug in libc, not in GStreamer.  Changing
> a few mallocs to allocas will not really make a dent in the usage
> patterns, anyway.
> 
> See also: http://c-faq.com/malloc/alloca.html

> 
> dave...
> 

In the one time use there is no saving when using alloca, thats right. Still
gstreamer uses malloc not in the best way (during GST_STATE_PLAY) and the issues
it causes is not the fault of the libc allocator. but thats another story.

Stefan