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

[Stefan Kost]

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.

>
>> * gst/gst.c: (_gst_disable_segtrap):
>>   Make  _gst_disable_segtrap static, it's only used in gstplugin.c and
>>   we can use gst_segtrap_is_enabled() there now that we have that API.
>>   Move _gst_debug_dump_dot_dir into gstdebugutils.c, there's no reason
>>   to do the getenv here (and export the variable).
>>
>> Hmm, I don't think we want to call getenv each time we dump a graph?
>
> Each time we dump a graph, we iterate through all elements and pads of a
> bin or pipeline, take and release hundreds of locks in the process, do a
> trizillion mallocs/frees/printfs, and WRITE TO DISK.  I fail to believe
> that a single call to getenv() before all that is going to have a
> significant performance impact.  If you have any evidence to the
> contrary, I'd love to see it :)

Its about when the env-var is *not* set. Then we just want to return  
quickly. Imaging having this in state_changed for each element. So  
instead of

   const gchar *dump_dot_dir;

   dump_dot_dir = g_getenv ("GST_DEBUG_DUMP_DOT_DIR");
   if (!dump_dot_dir)
     return;

what about
   static gboolean tested_dump_dot_dir = FALSE;
   static const gchar *dump_dot_dir = NULL;

   if( !tested_dump_dot_dir) {
     dump_dot_dir = g_getenv ("GST_DEBUG_DUMP_DOT_DIR");
     tested_dump_dot_dir = TRUE;
   }
   if (!dump_dot_dir)
     return;

Stefan

>
>  Cheers
>   -Tim
>
> PS: so what's next, a debate on the performance impact of ++i vs. i++?
>
>
>
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